AS & A2 Chemistry

Specimen Papers and Mark Schemes for

Chemistry

For fi rst AS Examination in 2009For fi rst A2 Examination in 2010

Subject Code: 1110

Contents Specimen Papers 1 Assessment Unit AS 1 3 Assessment Unit AS 2 17 Assessment Unit AS 3 29 Apparatus and Materials List 41 Assessment Unit A2 1 45 Assessment Unit A2 2 65 Assessment Unit A2 3 81 Mark Schemes 91 Assessment Unit AS 1 93 Assessment Unit AS 2 99 Assessment Unit AS 3 107 Assessment Unit A2 1 115 Assessment Unit A2 2 123 Assessment Unit A2 3 129 The Periodic Table of Elements 135 Answer Sheet 137

Further copies of this publication may be downloaded from www.ccea.org.uk

Subject Code 1110 QAN 500/2495/4 QAN 500/2494/2 A CCEA Publication © 2007

1

Specimen Papers

2

3

ADVANCED SUBSIDIARY (AS) General Certificate of Education

2009

Chemistry

Assessment Unit AS 1

assessing

Basic Concepts in Physical and Inorganic Chemistry TIME

1 hour 30 minutes INSTRUCTIONS TO CANDIDATES

Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all sixteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all six questions in Section B. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES

The total mark for this paper is 100. Quality of written communication will be assessed in question 16(a). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

Centre number

71

Candidate number

For Examiner’s use only

Question Number Marks

Section A 1-10

Section B 11 12 13 14 15 16

Total

Marks

4

Section A

For each of the following questions only one of the lettered responses (A-D) is correct. Select the correct response in each case and mark its code letter by connecting the dots illustrated on the answer sheet. 1 12.0 g of carbon-12 contains the same number of atoms as in:

A 2 g of helium, He B 48 g of sulphur dioxide, SO2 C one mole of atoms of iron, Fe D one mole of molecules of iodine, I2

2 Which one of the following species has a different number of electrons from the K+? A Ar B Br - C HS- D SiH4

3 An element has successive ionisation energies of 900, 1800, 14800 and 21000 kJmo1-1. To which Group of the Periodic Table does the element belong? A I B II C III D IV

4 What frequency of radiation in Hz is required to ionise helium? He He+ + e- ∆ H = +2370 kJmol-1

A 1.60 × 10-16

B 9.48 × 10-10 C 1.05 × 109 D 5.93 × 1015

5 Which one of the following is true of the halogens as the Group is descended from chlorine to iodine? A The atomic radius decreases. B The colour of the element lightens. C The melting point of the element increases. D The oxidising power of the element increases.

5

6 Which one of the following represents the shape of a p orbital?

7 Which one of the following represents the line emission spectrum of atomic hydrogen?

8 Iodine exists in different oxidation states from -1 to +7. Which one of the following iodine containing ions could not undergo disproportionation? A I+ B I- C IO- D IO3

-

6

9 The electronic energy levels of atomic hydrogen are shown below.

_____________________________ n = 4 _____________________________ n = 3

_____________________________ n = 2

___________________________ n = 1 The arrow on the diagram represents the energy change associated with the lowest frequency line in the: A ultraviolet absorption spectrum B ultraviolet emission spectrum C visible absorption spectrum D visible emission spectrum

10 Which one of the following equations represents the first ionisation energy of an element X? A X(s) X+(s) + e- B X(s) X+(g) + e- C X+(g) X2+(g) + e- D X(g) X+(g) + e-

7

Section B

Answer all six questions in the spaces provided. 11 (a) The first element in Group 7 is fluorine.

(i) Complete the table giving information about fluorine

Colour State at room

temperature Formula

Fluorine

(ii) The bar chart shows the atomic radius for some of the halogens.

State and explain the trend in atomic radius as the group is descended.

[3] [2]

8

●100

50

0

-50

●

●●

H2S

(b) Fluorides are beneficial in the prevention of dental cavities and are often added to toothpaste or to drinking water.

(i) State the formula of the fluoride ion.

(ii) Why do some people object to fluoride in drinking water but not in toothpaste?

[1] [1]

12 (a) The graph shows the variation of boiling points for the hydrides of Group 6.

Boiling temperature /oC

(i) Why is the boiling point of water higher than would be expected from the

group trend?

(ii) Why is the boiling point of H2Te higher than that of H2Se?

[2] [2]

H2Te

H2Se

H2O

9

(b) (i) Hydrogen sulphide (H2S) is produced when concentrated sulphuric acid is added to solid sodium iodide at room temperature. Name the other substances which are produced in this reaction.

[3]

(ii) State and explain two safety procedures which should be observed when carrying out the experiment in (i).

[2]

13 Rock salt is mined from the Kilroot mine outside Carrickfergus in Northern Ireland. The sodium chloride obtained from rock salt is used to manufacture chlorine by electrolysis of sodium chloride solution. (a) Use the s, p, d notation to show the formation of a sodium ion and chloride ion from

a sodium atom and a chlorine atom respectively and state the charge on each ion.

[4]

(b) When sodium chloride is placed in a Bunsen flame an intense yellow flame colour is noted. Explain how this flame colour is produced.

. [3]

10

(c) When concentrated sulphuric acid is added to sodium chloride, hydrogen chloride gas is produced.

(i) Write an equation for this reaction.

[1]

(ii) Calculate the concentration, in mol dm-3, of the solution formed when 19.6 g of hydrogen chloride are dissolved in water and the volume made up to 250 cm3.

[2]

(d) The melting point, boiling point and electrical conductivity of chlorine and some chlorine compounds were experimentally determined and recorded in the table shown below.

Substance Melting point

oC Boiling point oC

Electrical conductivity as solid

Electrical conductivity as liquid

sodium chloride

801 1465 Poor Good

beryllium chloride

405 488 Poor Poor

chlorine monofluoride

-157 -100 Poor Poor

chloride trifluoride

-76 12 Poor Poor

(i) Despite being a metal chloride, beryllium chloride does not conduct electricity.

Explain this observation.

________________________________________________________________

________________________________________________________________ (ii) Which of the compounds are polar?

________________________________________________________________

[1]

[1]

11

(iii) Suggest why the boiling point of chlorine trifluoride is much higher than chloride monofluoride.

________________________________________________________________ ________________________________________________________________

(iv) Explain why sodium chloride has the highest melting point.

________________________________________________________________

[1]

[1]

14 Titanium is a metal which is important in medicine and is used in hip and knee replacements, bone plates and in heart pacemakers. (a) (i) Give the electronic configuration of a titanium atom.

(ii) State the block in the Periodic Table to which titanium belongs.

(iii) Describe the bonding present in a metal such as titanium, and use this to explain its electrical conductivity.

[1] [1] [3]

(b) In a research laboratory a mass spectrum of a sample of titanium was experimentally determined. The spectrum showed five peaks. Use the data below to calculate the relative atomic mass of titanium in the sample to two decimal places.

m/e 46 47 48 49 50

% Abundance

8.02 7.31 73.81 5.54 5.32

[3]

12

(c) The most abundant isotope of titanium is 48Ti. State the number of protons, neutrons and electrons in an atom of this isotope.

[2]

(d) The metal titanium is obtained by the Kroll process in which titanium ore is converted into titanium chloride and then reduced using magnesium in an atmosphere of argon. 2Mg + TiC14 → 2MgC12 + Ti

(i) Deduce the oxidation numbers of titanium and magnesium in the reactants and products and use them to explain the redox change.

(ii) In industry 3800 kg of titanium chloride are added to 1500 kg of

magnesium. Use the headings below to help you calculate the maximum mass of titanium produced in this reaction.

number of moles of magnesium number of moles of titanium chloride

name of reactant in excess moles of titanium produced

mass of titanium produced

[3] [4]

(e) The electronegativity values of titanium and chlorine are shown below.

Ti 1.5 C1 3.0 (i) Define the term electronegativity.

[2]

13

(ii) Use the electronegativity values to show the polarity of the Ti – C1 bond.

Ti – C1

[1]

(iii) Explain why the TiC14 molecule is non polar, despite having polar bonds.

[1]

(f) Acidified potassium manganate (VII) (potassium permanganate, KMnO4) readily oxidises titanium (III) ions to titanium (IV) ions. Using the half equations below, write a balanced redox equation for the oxidation of titanium (III) ions to titanium (IV) ions by manganate (VII) ions.

MnO4

- + 8H+ + 5e- → Mn2+ + 4H2O Ti3+ → Ti4+ e-

[2]

15 (a) In the Haber process nitrogen and hydrogen react to produce ammonia gas. All these molecules contain covalent bonds.

(i) What is a covalent bond?

(ii) Draw a dot and cross diagram, using outer shell electrons only, to show the bonding in a nitrogen molecule, N2-.

(iii) Draw and name the shape of an ammonia molecule. Name

[2] [2] [2]

14

(b) Ammonia reacts with hydrogen chloride gas to form ammonium chloride which contains the NH4

+ ion.

(i) Write an equation for the reaction of ammonia with hydrogen chloride.

(ii) A bond in NH4+ can be represented by N → H. Name this type of bond and

explain how it is formed.

Name Explanation

[1] [2]

16 A solution of a weak acid H2X was made by dissolving 2.25 g of solid H2X in water to give 500 cm3 of solution. On titration, 25.0 cm3 of this solution was completely neutralised by 12.5 cm3 of standard 0.2 M sodium hydroxide solution.

H2X + 2NaOH → Na2X + 2H2O

(a) Describe, without details of rinsings, the practical steps required to accurately carry out this titration. In your answer name a suitable indicator for this titration and state the colour change which would be observed at the end point.

[6]

Quality of written communication

[2]

15

(b) (i) Calculate the number of moles of NaOH in 12.5 cm3 of 0.2 M sodium hydroxide solution.

[1]

(ii) How many moles of H2X would be required to react with this quantity of NaOH?

[1]

(iii) Use your answer from part (ii) to calculate the concentration of the H2X in mol dm-3.

[1]

(iv) Calculate the concentration of the H2X in g dm-3 using the mass of H2X measured out.

[1]

(v) From your answers to (iii) and (iv) calculate the relative molecular mass of H2X and identify X.

[2]

(c) A hydrated form of the solid acid also exists, H2X.yH2O. A solution containing 6.30 g dm-3 of the hydrated acid has the same concentration in mol dm-3 as the solution of the anhydrous acid, H2X, originally used.

(i) Use your answer from (b) (iii) and the information above to calculate the relative molecular mass of the hydrated acid.

[1]

(ii) Calculate the value of y.

[1]

(iii) Describe, giving experimental details, how you would remove all the water of crystallization from the solid hydrated acid.

[2]

16

17


2009

Chemistry


assessing

Further Physical and Inorganic Chemistry and Introduction to Organic Chemistry

TIME

1 hour 30 minutes INSTRUCTIONS TO CANDIDATES

Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all fifteen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all five questions in Section B. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES

The total mark for this paper is 100. Quality of written communication will be assessed in question 14(c). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

Centre number

71

Candidate number



Section A 1-10

Section B 11 12 13 14 15

Total

Marks

18

Section A For each of the following questions only one of the lettered responses (A – D) is correct. Select the correct response in each case by connecting the dots as illustrated on the answer sheet. 1 Which one of the following molecules would not be oxidised by acidified potassium

dichromate? A CH3CH2CH2OH B CH3CHCH3 OH C CH3 CH3 - C - CH3 OH D CH3CHCH2CH3 OH

2 The reaction between chlorine and methane can be described as: A free radical addition B free radical substitution C nucleophilic addition D nucleophilic substitution

3 Which one of the following would readily dissolve in water? A CH3CH2CH2Cl B CH3CH2CH2OH C CH3CH2CH3 D CH3CH=CH2

4 A solution of a salt gives a red colour when sprayed into a Bunsen flame and a white precipitate when added to silver nitrate solution. The salt is: A calcium sulphate B magnesium sulphate C potassium chloride D strontium chloride

19

5 Which one of the following alkenes exhibits cis-trans isomerism? A but-1-ene B but-2-ene C methylpropene D propene

6 Ethyl propanoate can be prepared by reaction between: A chloroethane and propanol B ethanoic acid and propanol C ethanoyl chloride and propanol D propanoyl chloride and ethanol

7 The catalyst used in the hardening of vegetable oils is: A nickel B palladium C platinum D vanadium (V) oxide

8 Which one of the following is not a source of ethanol? A Manufacture from cane sugar B Calalytic hydration of ethene C Hydrolysis of bromoethane with alkali D Reaction of ethanal with acidified potassium dichromate

9 Which one of the following statements about ethene is correct? A The pi bond is formed by sideways overlap of two s orbitals B The pi bond is readily attacked by electrophiles C The double bond rotates freely at room temperature D It is a saturated hydrocarbon

10 In the infra-red spectrum of an organic compound, a strong band is observed at 3000 cm-1. The most likely explanation is: A bonding electrons absorb radiation and are excited to a higher level B the compound is being decomposed by the radiation C protons absorb infra-red radiation at this frequency D radiation is absorbed and causes the C-H bonds to vibrate

20

Section B

Answer all five questions in the space provided. 11 The Haber process for the production of ammonia involves the equilibrium reactions

between nitrogen and hydrogen. (a) Write the equation for the equilibrium reaction.

(b) Name the catalyst used in the Haber process.

(c) Explain why a combination of high pressure and moderate temperature

maximises the yield of ammonia.

High pressure Moderate temperature

(d) Describe a chemical test for ammonia.

[2] [1] [2] [2] [2]

21

12 Branched chain alkanes such as 2,2,4-trimethylpentane (isooctane) ignite less easily than straight chain alkanes in a car engine and their combustion is much more controlled. (a) Suggest the structural formula for 2,2,4-trimethylpentane

[2]

(b) Deduce the molecular and empirical formula for 2,2,4-trimethylpentane

(i) molecular formula (ii) empirical formula

(c) The combustion of isooctane may occur in a limited or a plentiful supply of air.

Name the products of combustion in each case.

(i) limited supply of air

(ii) plentiful supply of air

[1] [1] [2] [2]

(d) In a car engine a mixture of hydrocarbon vapour and air is compressed in what is known as the compression stroke and hence the total volume of gas is reduced. Explain, in terms of collision theory, how this will increase the rate of combustion.

[2]

22

(e) In the exhaust stroke the gaseous products escape. Calculate the volume of carbon dioxide produced, at room temperature and pressure, if 1 mg of octane, C8H18, is completely combusted. (One mole of carbon dioxide occupies a volume of 24000 cm3 at room temperature and pressure). Write the equation for the complete combustion of octane. Calculate the number of moles of octane in 1 mg.

Calculate the number of moles of carbon dioxide produced.

Calculate the volume of carbon dioxide produced.

[4]

(f) In cars, the exhaust gases pass through a catalytic converter.

(i) Name a metal used as a catalyst in the converter.

(ii) What happens to unburned carbon monoxide as it passes through the converter?

(iii) Why is this catalysis described as heterogeneous?

[1] [1] [1]

23

13 1-bromobutane, C4H9Br, is a liquid halogenoalkane which may be prepared by refluxing butan-1-ol, C4H9OH, with sodium bromide and concentrated sulphuric acid. Purification requires distillation, removal of acidic impurities using sodium hydrogencarbonate, drying the product and final distillation. (a) The sodium bromide and concentrated sulphuric acid react to form hydrogen

bromide which reacts with the butan-1-ol.

(i) Write an equation for the reaction between butan-1-ol and hydrogen bromide.

(ii) What is meant by the term reflux?

[2] [2]

(b) A separating funnel is used to shake the crude product with sodium hydrogencarbonate solution. Explain why pressure builds up inside the funnel and how this pressure is released periodically.

(c) Name a suitable drying agent for this preparation.

(d) A student used 11.0 g of butan-1-ol and obtained 12.5 g of 1-bromobutane.

Calculate the percentage yield.

[3] [2] [3]

24

(e) 1-bromobutane is a primary halogenoalkane and is readily hydrolysed by aqueous hydroxide ions.

(i) Name the mechanism by which aqueous hydroxide ions react with

1-bromobutane.

(ii) Draw a flow scheme for the mechanism of this reaction. (f) Hydroxide ions in alcohol react differently with 1-bromobutane.

(i) State the type of reaction occurring.

(ii) Name, or give the structural formula, of the organic product in this reaction.

[2] [3] [1] [1]

25

14 The group II elements, together with their electron structure, are listed below: beryllium 1s2 2s2 magnesium 1s2 2s2 2p6 3s2 calcium 1s2 2s2 2p6 3s2 3p6 4s2 strontium 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s2 barium 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s2 (a) Explain why they are regarded as s-block elements.

(b) (i) State and explain the trend in atomic radius down the group.

(ii) State and explain the trend in first ionisation energies down the group.

(c) Giving observations only, compare the chemistry of calcium with that of

magnesium using the following headings:

Combustion

[1] [2] [3] [2]

Reaction with water Reaction with dilute hydrochloric acid


[2] [2] [2]

26

(d) Calcium oxide is basic and reacts with water to form the hydroxide.

(i) Explain the term basic.

(ii) Write an equation for the reaction of calcium oxide with water.

(iii) If the solubility of calcium hydroxide is 0.021 mol dm-3 at 20oC, calculate the number of grams of calcium hydroxide which would dissolve in 250 cm3 of water at that temperature.

(e) Calcium hydroxide reacts with hydrochloric acid to form calcium chloride and

water.

Write the equation for this reaction.

[1] [1] [3] [2]

27

15 In South America, ethanol, C2H5OH, is used as a fuel for motor vehicles. (a) Draw a labelled enthalpy level diagram for the complete combustion of ethanol

in oxygen. (b) In an experiment the combustion of 0.4 g of ethanol raises the temperature of

100 g of water by 20.5oC. Calculate the enthalpy of combustion of one mole of ethanol.

(Assume that 4.2 J are required to raise the temperature of 1 g of water by 1oC)

[3] [4]

28

(c) The bond enthalpies of some common bonds are given below:

Bond kJmol-1

C – C +347 C – H +413 C – O +358 C = O +805 O – H +464 O = O +498

Use these values to calculate the enthalpy change for the combustion of one mole of ethanol.

C2H5OH + 3O2 → 2CO2 + 3H2O

(d) The experimental molar enthalpies of combustion for methanol and ethanol are: Methanol CH3OH -726 kJ Ethanol C2H5OH -1367 kJ Calculate which alcohol produces most energy when 1g of each is burnt.

[4]

[3]

29


2009

Chemistry


Internal Assessment

SPECIMEN PAPER TIME

2 hours 30 minutes INSTRUCTIONS TO CANDIDATES

Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all eleven questions. Write your answers to questions 1–3 in the spaces provided. Record your answers to questions 4–11 by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 4 to 11. Keep in sequence when answering. INFORMATION FOR CANDIDATES

The total mark for this paper is 90.

Section A Questions 1 and 2 are practical exercises each worth 25 and 29 marks respectively.

Section B Question 3 is a planning exercise worth 20 marks. Questions 4–11 all carry equal marks, i.e. two marks for each question. You may not have access to notes, textbooks and other material to assist you. A Periodic Table of Elements (including some data) is provided.

Centre number

71

Candidate number

For Examiner’s use only Question Number

Marks Moder-ation Marks

Section A 1 2

Section B 3

4-11 Total

Marks

30

Section A 1 Titration exercise

Task Identify the metal, M, in a solution of its metal hydroxide, MOH. You are provided with:

Sulphuric acid solution 0.05 mol dm-3. Metal hydroxide (MOH) solution of concentration 5.33 g dm-3. Phenolphthalein indicator. You are required to titrate the sulphuric acid solution against the metal hydroxide solution using phenolphthalein as indicator and use your results to identify metal M. Give details of the procedures you would use, the expected colour change of the indicator, a completed results table, any equations needed and any calculations.

(a) Procedure:

[4]

31

(b) Results table:

[12] (c) Colour change of indicator:

[1] (d) Relevant equation:

[2] (e) Calculations:

32

[5]

(f) Conclusion:

[1]

33

2 Observation/deduction

Safety goggles must be worn at all times and care should be exercised during this practical examination. You are provided with two unknown substances: 3 g of a substance labelled A and 5 cm3 of a solution labelled B. Carry out the following experiments on A and B. Record your observations and deductions in the space below.

(a)

Experiment

Observations Deductions

(i) Describe A.

(ii) Fill a test tube full of water and record the temperature.

Add three spatula measures of A to the test tube, stir and note the temperature.

(iii) Add 3 drops of the solution formed in (ii) to another test tube.

Acidify with 3 drops of dilute nitric acid and then add 1 cm3 of silver nitrate solution.

Add 5 cm3 of dilute ammonia solution to the test tube.

(iv) Add a spatula measure of A to a test tube one third full of dilute sodium hydroxide solution and warm gently, testing any gas evolved with moist pH paper.

A is:

34

(b)

Experiment


(i) Describe the smell of solution B.

(ii) Using a glass rod place a drop of B onto pH paper.

(iii) Add a spatula measure of anhydrous sodium carbonate to a test tube one quarter full of solution B and identify the gas evolved using a suitable reagent.

(iv) Add 1 cm3 of B to a test tube. Add a 2 cm length of magnesium ribbon.

B is:

[29]

35

Section B 3 You are required to plan an experiment to identify a Group II carbonate, MCO3. A

suitable amount of the carbonate is 5 g. If this is heated to constant mass the relative atomic mass of M may be determined and M identified. The equation for the action of heat on the metal carbonate is:

MCO3 → MO + CO2

(a) (i) Draw a diagram of apparatus which could be used in heating the carbonate sample to constant mass.

(ii) Other than the wearing of safety glasses, state one safety precaution involved in the experiment.

[3] [1]

(b) (i) What weighing(s) must be recorded before heating the sample?

(ii) Explain the term heated to constant mass.

[1] [2]

36

(c) Suppose that 4.90 g of MCO3 yields 2.33 g of MO.

(i) What is the mass of carbon dioxide evolved?

[1]

(ii) What is the number of moles of carbon dioxide evolved?

(iii) What is the number of moles of the metal oxide, MO?

(iv) What is the relative atomic mass of the metal, M?

(v) Identify the metal, M.

[1] [1] [1] [1]

(d) The gas evolved is carbon dioxide.

(i) How would you prove this using a chemical test and what would be observed?

(ii) Write an equation for the reaction between carbon dioxide and the reagent

in the chemical test.

[2] [2]

37

(e) It is possible to find the relative atomic mass of M by a method involving the addition of excess hydrochloric acid to the metal carbonate. The unreacted acid is determined by titration with standard sodium hydroxide solution.

(i) Write an equation for the reaction of the metal carbonate with hydrochloric

acid.

(ii) What is meant by standard?

(iii) State an indicator which would be suitable for the titration of the excess acid.

[2]

[1]

[1]

4 Which of the following describes a test for chlorine? A Universal indicator goes blue and is then bleached. B Universal indicator goes red and is then bleached. C Universal indicator goes blue. D Universal indicator goes red.

5 The apparatus below shows a method for obtaining carbon monoxide. Carbon dioxide is passed over hot charcoal.

CO2 + C → 2CO

What are the names of X and Y? X Y A calcium carbonate concentrated sulphuric acid B calcium carbonate limewater C calcium sulphite limewater D calcium sulphite concentrated sulphuric acid

38

6 4.2 g of 1-bromobutane (RMM 137) were obtained in a preparation from butan-1-ol (RMM 74). What mass of butan-1-ol was used if the yield was 75%? A 1.7 g B 3.0 g C 5.8 g D 10.3 g

7 An unknown salt is tested by:

(a) dissolving in water, adding dilute nitric acid followed by silver nitrate solution and then adding concentrated ammonia solution.

(b) dissolving in concentrated hydrochloric acid and carrying out a flame test. The first test resulted in a cream precipitate which dissolved in an excess of ammonia. The second test produced a green flame. The salt is: A barium bromide B calcium chloride C copper iodide D strontium bromide

8 In the determination of the purity of a sample of magnesium carbonate by a back titration method, which one of the following statements is incorrect? A Phenolphthalein or methyl orange are suitable indicators. B The amount of excess acid remaining is determined by titration with standard

alkali. C The sample is reacted with excess alkali. D Unreacted magnesium carbonate is filtered off and weighed.

9 4.35 g of potassium sulphate, K2SO4, is dissolved in water and made up to 100 cm3. What is the concentration of potassium ions in mol dm-3. A 0.025 B 0.050 C 0.250 D 0.500

39

10 Which one of the following ions, in aqueous solution, reacts with magnesium ions to form a colourless solution which deposits a white precipitate on boiling. A sulphite B hydroxide C hydrogencarbonate D carbonate

11 The graph below represents the change in pH as 25 cm3 of a 0.1 mol dm-3 solution of an alkali is titrated against a 0.1 mol dm-3 solution of acid.

Which one of the following acid-alkali pairs could this graph represent? A sodium hydroxide hydrochloric acid B sodium hydroxide ethanoic acid C ammonia solution hydrochloric acid D ammonia solution ethanoic acid

40

41


2009

Chemistry


assessing

Internal Assessment

APPARATUS AND MATERIALS LISTS

42

Apparatus and Materials List for AS 3A Specimen Paper Section A Question 1 Each candidate should be supplied with: • one 50 cm3 burette of at least class B quality; • one 25 cm3 pipette of at least class B quality; • a safety pipette filler; • three conical flasks of about 250 cm3 capacity; • a funnel for filling the burette; • a tile or clean white paper as a background; • two beakers of about 100 cm3 capacity; • a wash bottle; • a retort stand and clamps; • about 150 cm3 of sodium hydroxide solution in a beaker labelled MOH made up by diluting

20 cm3 of 1.0 M sodium hydroxide solution to 150 cm3 or preparing a solution of concentration 5.33 g dm-3 made up using deionised water;

• about 150 cm3 of 0.05 mol dm-3 sulphuric acid and a beaker labelled 0.05 M sulphuric acid and irritant. The sulphuric acid should be prepared using an accurately prepared commercial standard, such as BDH CONVOL solutions;

• phenolphtalein indicator in a dropping bottle; • a supply of deionised or distilled water.

43

Apparatus and Materials List for AS 3B Specimen Paper Section B Question 2 Each candidate should be supplied with: • five test tubes (125 mm length × 16 mm OD would be suitable); • a 10 cm3 measuring cylinder; • a test tube holder; • a test tube rack; • a spatula; • a Bunsen burner; • a glass rod; • universal indicator/pH paper; • five drippers with teats; • about 3.0 g ammonium chloride labelled A; • about 10 cm3 of dilute nitric acid in a reagent bottle labelled dilute nitric acid and irritant.

This solution should be approximately 2 M; • about 10 cm3 of silver nitrate solution in a reagent bottle labelled silver nitrate solution. This

solution should be approximately 0.1 M (17.0 g dm-3); • about 20 cm3 of aqueous ammonia in a stoppered reagent bottle labelled dilute ammonia

solution and irritant. This solution should be approximately 2 M; • about 20 cm3 of sodium hydroxide solution in a reagent bottle labelled dilute sodium

hydroxide solution and irritant. This solution should be approximately 0.5 M (20 g dm-3); • about 10 cm3 of dilute ethanoic acid in a reagent bottle labelled B and irritant. The solution

should be approximately 2 M and can be prepared from concentrated ethanoic acid; • two 2 cm lengths of magnesium ribbon labelled magnesium ribbon; • 1 g of anhydrous sodium carbonate in a beaker labelled anhydrous sodium carbonate.

44

45

ADVANCED General Certificate of Education

2010

Chemistry

Assessment Unit A2 1

assessing

Periodic Trends and Further Organic, Physical and Inorganic Chemistry

SPECIMEN PAPER

TIME

2 hours INSTRUCTIONS TO CANDIDATES

Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all twenty questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all ten questions in Section B. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES

The total mark for this paper is 120. Quality of written communication will be assessed in question 19(c). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

Centre number

71

Candidate number



Section A 1-10

Section B 11 12 13 14 15 16 17 18 19 20

Total

Marks

46

Section A

For each of the following questions only one of the lettered responses (A-D) is correct.

Select the correct response in each case by connecting the dots as illustrated on the answer sheet.

1 Which one of the following equations represents the lattice enthalpy of magnesium

chloride?

A Mg(s) + Cl2(g) → MgCl2(s) B MgC12(s) → Mg(s) + C12(g)

C Mg2+(g) + 2Cl (g) → MgC12(s) D MgC12(s) → Mg2+(g) + 2Cl−(g)

2 X and Y react with each other according to the rate equation:

rate = k[X][Y]2 Which one of the following represents the relationship between the rate and the concentration of Y?

3 Ammonium chloride is acidic in aqueous solution due to the dissociation of the ammonium ion.

NH4+(aq) NH3(aq) + H+(aq) Ka = 5.7 × 10-10

mol dm-3

What is the pH of a 0.1 M aqueous solution of ammonium chloride? A 1.0 B 5.1 C 6.1 D 11.2

4 The mechanism for the reaction between hydrogen cyanide and propanone is described as: A electrophilic addition. B electrophilic substitution. C nucleophilic addition. D nucleophilic substitution.

47

5 Which one of the following indicators would be suitable for use in a titration of 0.1 M sodium hydroxide solution against 0.1 M ethanoic acid solution?

Indicator pH range of colour change

A Cresol red 1.0−2.0

B α−Naphthyl red 4.0−5.7

C Thymol blue 8.0−9.6

D 1,3,5−trinitrobenzene 12.0−14.0

6 Overall, the rate of reaction between Y and Z is third order. Which one of the following equations is not correct? A Rate = k [Y]0 [Z]3 B Rate = k [Y]1 [Z]2 C Rate = k [Y]1 [Z]3 D Rate = k [Y]2 [Z]1

7 Which one of the following oxides does not act as an acid? A A12O3 B C12O7 C MgO D SiO2

8 Which one of the following compounds produces a silver mirror when heated with Tollen’s reagent? A CH3CH2COOH B CH3CH2CHO C CH3COCH3 D CH3COOCH3

9 25.0 cm3 of an aqueous solution containing 5.0 g of a solute X is shaken with 15.0 cm3 of ether in a separating funnel. What mass of X remains in the aqueous layer if the partition coefficient for X between ether and water is 3.3? A 0.6g B 1.2g C 1.7g D 1.8g

10 Dinitrogen tetroxide, N2O4, and nitrogen dioxide form an equilibrium mixture at 300K.

N2O4(g) 2NO2(g)

If the equilibrium concentration of N2O4 is 1.52 mol dm−3 and Kc is 1.0 × 10−5 mol dm−3

, the equilibrium concentration of NO2, in mol dm−3, is

A 1.5 × 10−5 B 3.9 × 10−3

C 2.6 × 102 D 6.6 × 104

48

Section B

Answer all ten questions in the spaces provided. 11 Lactic acid has the formula CH3CHOHCOOH and the molecule is optically active.

Explain the term optically active and draw the three dimensional structures of the two chiral isomers. (a) optically active

[2]

(b) chiral isomers

⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜

[3]

49

12 The partially completed Born-Haber cycle for potassium chloride is shown below. (a) Complete the empty boxes.

[2]

(b) Using the data below, calculate the enthalpy of formation for potassium chloride.

kJ mol–1

First ionisation energy of potassium +418 Enthalpy of atomisation of potassium +90 Bond enthalpy of chlorine +242 Electron affinity of chlorine −348 Lattice enthalpy of potassium chloride +701

enthalpy of formation ______________________ kJ mol–1

[2]

K+(g) + Cl(g) + e–

K(s) + 21 Cl2(g)

K+(g) + Cl– (g)

KCl(s)

50

13 Calcium carbonate undergoes thermal decomposition according to the following equation:

CaCO3 (s) → CaO (s) + CO2 (g)

(a) Use the data in the table below to calculate the standard enthalpy change

(ΔH ) and the standard entropy change (ΔS ) for this reaction.

Substance CaCO3 (s) CaO (s) CO2 (g)

ΔHf /kJmol−1 −1207 −635 −394

S /J K−1mol−1 90 40 214

(i) Standard enthalpy change (ΔH )

(ii) Standard entropy change (ΔS )

[2] [2]

(b) Use the answers obtained in part (a) to explain why this reaction is not feasible at 298K.

[3]

(c) Use the answers obtained in part (a) to calculate the minimum temperature at which this reaction is feasible.

[3]

51

14 Neopentyl bromide is a dense liquid with a boiling point of 189°C. It is insoluble in water but reacts with aqueous alkali to form neopentyl alcohol:

(a) Give the systematic name for neopentyl bromide.

[2]

(b) The hydrolysis of neopentyl bromide was investigated using aqueous sodium hydroxide solution, and the following results were obtained:

Experiment [neopentyl bromide]

(mol dm−3 )

[OH−] (mol dm−3 )

Rate (mol dm−3 s−1 )

1 0.02 0.01 0.68

2 0.02 0.04 2.72

3 0.04 0.04 5.44

(i) What is the order of the reaction with respect to neopentyl bromide?

(ii) What is the order of the reaction with respect to hydroxide ions?

(iii) Write the rate equation for the hydrolysis of neopentyl bromide.

(iv) Calculate a value for the rate constant and state its units.

[1] [1] [1] [2]

52

(v) Draw a flow scheme of the mechanism for the hydrolysis of neopentyl bromide.

[3]

53

15 Hydrogen gas, required in the Haber process, may be produced by the reaction:

CH4(g) + H2O(g) CO(g) + 3H2(g) ΔH = +206 kJ

(a) Explain how the equilibrium concentration of hydrogen gas would be affected by increasing the pressure.

[2]

(b) A mixture of 120 g of methane and 108 g of steam was allowed to reach equilibrium at 400°C and 250 atmospheres pressure. When equilibrium was established 32 g of methane remained. Calculate Kp, stating its units.

[4]

54

16 The pH changes during the titration of nitric acid with alkaline solutions can be shown using titration curves. (a) The curve for the titration of 0.1 M nitric acid with 0.1 M sodium hydroxide is

shown below.

(i) Write the ionic equation for the reaction.

(ii) Calculate the pH at point X when 20 cm3 of 0.1 M sodium hydroxide is added to 25 cm3 of 0.1 M nitric acid.

[1] [3]

55

(b) The titration curve for the reaction of 0.1 M nitric acid with 0.1 M ammonia solution is shown below.

(i) Write the equation for the protonation of ammonia.

(ii) Name a suitable indicator for the titration.

(iii) Using the titration curve explain why this indicator is suitable.

[1] [1] [2]

(c) The neutralised solution contains ammonium nitrate. Explain why it is acidic.

[2]

56

(d) The table below shows the results obtained when 0.1 M NaOH was added to 25.0 cm3 of a solution containing ethanoic acid.

Initial reading

(cm3) Final reading

(cm3) Titre (cm3)

Rough

0.0

12.0

1st accurate

12.0

23.8

2nd accurate

23.87

35.6

(i) Complete the table and use the results to work out the concentration (molarity) of the ethanoic acid solution.

[5]

57

(ii) Incomplete neutralisation of a weak acid by a strong base results in a buffer solution. When 15.0 cm3 of a 0.1 M solution of NaOH is added to 30.0 cm3 of a 0.1 M solution of butanoic acid, the resulting solution has a pH = 4.82. Use this information to calculate the acid dissociation constant Ka for butanoic acid.

[5]

58

17 The “new-car” smell, which many consider attractive, comes from the “outgassing” of organic molecules from the plastic components. These molecules include propanone, benzene and phthalate esters. The presence of propanone may be confirmed by drawing the air from the car, over a long period of time, through a solution of 2,4-dinitrophenylhydrazine.

(a) Draw the structure of propanone.

[1]

(b) Write the equation for the reaction between propanone and 2,4-dinitrophenylhydrazine.

[2]

(c) State what is observed when the 2,4-dinitrophenylhydrazone is formed.

[1]

(d) How would you use the pure 2,4-dinitrophenylhydrazone to confirm the ketone as propanone?

[2]

59

18 There are four pentanoic acids with the formula, C5H10O2. (a) Draw the structure of the pentanoic acid which is chiral and label the

asymmetric centre with an asterisk (*).

[2]

(b) The best known pentanoic acids are valeric acid and isovaleric acid.

CH3CH2CH2CH2COOH (CH3)2CHCH2COOH valeric acid isovaleric acid

State the systematic name for isovaleric acid.

[2]

(c) Both valeric and isovaleric acids occur in the root of the valerian plant and can be extracted using aqueous sodium carbonate. The extract from the dried roots has been used for treating muscle spasms and lowering blood pressure (Latin: valere = to be healthy).

(i) Write the equation for the reaction of valeric acid with sodium carbonate.

(ii) Explain how you would reform the valeric acids from the aqueous

solution.

[2] [1]

60

(d) Isovaleric acid is produced in the body as a result of a disorder of amino acid metabolism. It is known as sweaty foot syndrome because of the intense odour of the acid.

Calculate the concentration of isovaleric acid in mol dm-3 (of air) if 5.00 �l are vaporised in 80 dm3 of air at 20°C and one atmosphere pressure. The density of the acid, which is a liquid, is 0.95 g cm-3 at 20°C.

(�l = microlitre = 1 × 10-6 litre)

. [3]

(e) The valeric acids are reacted with alcohols to make esters which are used in the manufacture of flavourings, perfumes and lubricants.

(i) Write the equation for the reaction of valeric acid with ethanol.

(ii) State two ways by which the rate of esterification can be increased.

[2] [2]

61

19 No fat is entirely saturated or unsaturated whether it is of animal or vegetable origin. A highly unsaturated fat is called a polyunsaturate. Lard is a mainly saturated fat while palm-kernel oil is mainly unsaturated. (a) Name the triol involved in the formation of fats.

[1]

(b) Explain the term polyunsaturate.

[1]

(c) Explain how you would determine, by experiment, the iodine value of lard. No equations or calculations are required.


[5] [2]

(d) (i) A high saponification value signifies that a fat is formed from fatty acids of low relative molecular mass. Define the term saponification value.

[2]

62

(ii) 40 cm3 of a solution of 0.125 M potassium hydroxide, in ethanol, were refluxed with 0.80 g of a fat for 40 minutes. The reaction mixture was then titrated against 0.125 M HCl and 23.0 cm3 were required for neutralisation. Determine the saponification value of the fat.

[4]

(e) What is the name given to the process of changing an oil to a fat such as margarine?

[1]

63

20 The oxides and chlorides of elements of the third period show a change in character from ionic to covalent. (a) Write the equation for the reaction of sodium oxide with water.

[2]

(b) The increase in covalent character across the third period is illustrated by the fact that aluminium oxide is amphoteric.

(i) Explain the term amphoteric.

(ii) Write the equation for the reaction of aluminium oxide with aqueous

sodium hydroxide.

[1] [2]

(c) The Al2Cl6 molecule contains two coordinate bonds.

(i) Draw a diagram of the Al2Cl6 molecule showing all the bonds present.

[2]

(ii) Write the equation for the reaction of Al2Cl6 with water.

[2]

64

65


2010

Chemistry


assessing

Analytical, Transition Metals, Electrochemistry and Further Organic Chemistry

SPECIMEN PAPER TIME

2 hours INSTRUCTIONS TO CANDIDATES

Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all seventeen questions. Answer all ten questions in Section A. Record your answers by marking the appropriate letter on the answer sheet provided. Use only the spaces numbered 1 to 10. Keep in sequence when answering. Answer all seven questions in Section B. Write your answers in the spaces provided in this question paper. INFORMATION FOR CANDIDATES

The total mark for this paper is 120. Quality of written communication will be assessed in question 16(a). In Section A all questions carry equal marks, i.e. two marks for each question. In Section B the figures in brackets printed down the right-hand side of pages indicate the marks awarded to each question or part question. A Periodic Table of Elements (including some data) is provided.

Centre number

71

Candidate number



Section A 1-10

Section B 11 12 13 14 15 16 17

Total Marks

66

Section A For each of the questions only one of the lettered responses (A-D) is correct Select the correct response in each case and mark its code letter by connecting the dots as illustrated on the answer sheet. 1 Which one of the following sets of reagents is used in the laboratory preparation of

K2SO4. Cr2(SO4)3.24H2O? A Potassium dichromate, sulphuric acid and ethanol B Potassium chromate, sulphuric acid and ethanol C Potassium sulphate, chromium sulphate and ethanal D Potassium dichromate, sulphuric acid and ethanal

2 Which one of the following compounds is the most basic? A NH3 B CH3CONH2 C NH2CH2COOH D CH3CH2NH2

3 Benzene diazonium chloride is normally used in aqueous solution at temperatures less than 5oC, rather than in the crystalline form, because the solid

A couples B decomposes C oxidises D polymerises

67

4 Which one of the following structures is that of the benzene diazonium ion?

+ +

A N=N B N≡N

+ +

C N=N D N≡N

5 The reaction represented by the equation below CH3CH2CH2Cl + NH3 → CH3CH2CH2NH3

+ + Cl- is described as: A electrophilic addition B electrophilic substitution C nucleophilic addition D nucleophilic substitution

6 The diagram below shows the titration of a solution of magnesium ions with edta using Eriochrome Black T as indicator.

What is the colour change at the end-point? A blue to red B green to blue C red to green D red to blue

68

7 How many electrons are there in the delocalised π electron system in a benzene ring?

A 3 B 6 C 12 D 18

8 Which one of the following syntheses can be used to prepare iodobenzene in the laboratory.

+ A N2Cl– + I2 → I + ICl + N2

B Cl + KI → I + KCl

C + I2 → I + HI

+ D N2Cl– + KI → I + KCl + N2

9 Which one of the following structures is that of an anti-cancer drug?

A Cl B Cl Pt Pt NH3 Cl NH3 NH3 NH3 Cl C NH3 NH3 D NH3 Cl Pt Pt Cl Cl Cl NH3

69

10 Which one of the following equations shows hydrogen peroxide acting as an oxidising agent? A CO3

2- + H2O2 → CO2 + O2

2- + H2O B O3 + H2O2 → 2O2 + H2O C 2Fe(CN)6

3- + H2O2 + 2OH- → O2 + 2Fe(CN)6

4- + 2H2O

D 2Fe2+

+ H2O2 + 2H+ → 2Fe3+ + 2H2O

70

Section B

Answer all seven questions in the spaces provided. 11 Complete the flow scheme below by writing the formulae of the four nickel

compounds formed. OH- edta4- Ni2+ NH3 en

[4]

12 Glycine is an amino acid which exists as a white solid that melts at 289-293oC. (a) The high melting point of glycine is a result of the formation of a zwitterion.

(i) Write the formula of the zwitterion.

(ii) Explain the high melting point of glycine.

(b) Hippuric acid, C6H5CONHCH2COOH, is found in horse’s urine.

Write an equation to show the formation of hippuric acid from glycine.

[1] [2] [2]

71

(c) Glycine reacts with sodium carbonate.

(i) Write an equation for the reaction.

(ii) Calculate the volume of carbon dioxide produced at 20oC and at a

pressure of one atmosphere when 3.0 g of glycine react with 8.4 g of sodium carbonate.

[2] [4]

(d) Esterification of glycine removes its acidity.

(i) Write an equation for the reaction of glycine with methanol.

(ii) Explain why a mixture of amino acids is often converted into esters before analysis by GLC.

[1] [2]

72

13 The diagram below shows a two-way chromatogram obtained from the hydrolysis of insulin.

(a) How can insulin be hydrolysed as quickly as possible?

(b) What name is given to the substances on the chromatogram?

(c) Name the reagent used to detect the substances and state the result of a positive

result.

(d) Using the chromatogram deduce what type of substance insulin is.

(e) Explain how you would run and develop a two-way chromatogram using

hydrolysed insulin.

[2] [1] [2]

[1] [4]

73

(f) Every separated substance on the chromatogram has a unique Rf value. Define the term Rf.

[1]

14 Butanone is a pleasant smelling liquid with a boiling point of 80oC. It is widely used as a solvent for vinyl resins and synthetic rubber. (a) Butanone is prepared industrially by passing butan-2-ol vapour over copper at

300oC. CH3CHOHCH2CH3 CH3COCH2CH3 + H2 Butanone is obtained together with a small proportion of butan-2-ol.

(i) Using equilibrium principles, explain whether the preparation should be carried out at low or high pressure.

(ii) How would you purify the butanone?

[2] [2]

74

(b) The nmr spectrum of butanone is shown below.

(i) Explain why the peak at 2.1 ppm is a singlet.

(ii) Explain why the quartet at 2.4 ppm has the highest value (ppm) in the spectrum.

[1] [1]

(iii) Explain why the signal at 1.0 ppm is a triplet.

(iv) Explain how the integration curve can be used to identify the hydrogen

atoms responsible for the spectrum.

(v) Give two reasons why tetramethylsilane is used as a standard in nmr spectroscopy.

[1] [2] [2]

75

(c) Two of the major peaks in the mass spectrum of butanone occur at m/e values of 29 and 43. Identify the ions.

29 43

[1] [1]

(d) Explain how mass spectrometry can be linked with GLC to monitor the industrial production of butanone.

[3]

15 Vanadium is a typical transition metal, atomic number 23. It is a hard silvery-white metal which is oxidised when strongly heated in air. Compounds of vanadium exist where the metal has an oxidation state of +2, +3, +4 and +5 which are associated with the colours violet, green and blue and yellow in aqueous solution.

(a) State three reasons to classify vanadium as a transition metal.

(b) Write the electronic configuration for a vanadium atom.

(c) (i) Write the formula of the oxide of vanadium where vanadium has its

highest oxidation state.

(ii) State a use of this oxide in a chemical process.

[3] [1] [1] [2]

76

(d) Acidified ammonium vanadate forms the VO2+ ion when acidified. Use the

standard electrode potentials shown below to answer the following questions.

Eo/V

Zn2+(aq) + 2e Zn(s) -0.8 V3+(aq) + e V2+(aq)

-0.3 VO2+(aq) + 2H+(aq) + e V3+(aq)

+ H2O(l) +0.3

VO2+(aq) + 2H+(aq) + e VO2+(aq)

+ H2O(l) +1.0 MnO4

-(aq) + 8H+(aq) + 5e Mn2+(aq) + 4H2O(l) +1.7

(i) Explain the sequence of colour changes when zinc is added to acidified ammonium vanadate.

(ii) Explain whether acidified manganate (VII) will oxidize V(III) to V (IV).

Identify the two half equations involved and the direction in which the equilibria move.

(iii) Write the equation for the reaction of acidified manganate (VII) with

VO2+ ions.

[3] [2] [2]

77

(e) Vanadium occurs in the class of enzymes known as vanadium haloperoxidases which are of potential industrial importance.

Outline the way by which enzymes catalyse biological reactions and the probable effect of pH and temperature on the activity of a vanadium haloperoxidase.

[5]

16 β-Carotene is one of the bright yellow-orange compounds in carrots. It contains eleven double bonds and is known as a polyene. It is also called a provitamin because it can be converted into vitamin A.

(a) Explain, using delocalisation and energy levels why β-Carotene has a yellow-orange colour.


[4] [2]

78

(b) Vitamins are classified as fat-soluble or water-soluble. Suggest why β-carotene is fat-soluble.

[2]

(c) The number of double bonds in a molecule can be determined by catalytic hydrogenation.

(i) 0.0129 g of a hydrocarbon of formula, C7H8, absorbs 103 cm3 of hydrogen

at 20oC and one atmosphere pressure. Calculate the number of double bonds in the molecule.

(One mole of hydrogen occupies 24 dm3 at 20oC and one atmosphere pressure)

[3]

(ii) Name the metal used in the hydrogenation and use chemisorption to explain how it catalyses the reaction.

[4]

(d) β-Carotene has been recommended for the prevention of cancer as the double bonds present react with oxygen and free radicals implicated in the onset of cancer. On the other hand double bonds in cyclic systems such as benzene do not act in the same way. Explain the relative reactivities of benzene and alkenes.

[4]

79

17 Potassium manganate (VII) is a powerful oxidising agent which is capable of oxidising nitrites to nitrates and ethanedioates (oxalates) to carbon dioxide. (a) Potassium manganate (VII) solution oxidises nitrites to nitrates according to the

equation below: 3H2SO4 + 2KMnO4 + 5KNO2 → K2SO4 + 2MnSO4 + 3H2O + 5KNO3

Rewrite this equation as an ionic equation where all the ions, which feature on both sides of the equation, are cancelled out.

[2]

(b) Potassium manganate (VII) may be used to determine the concentration of sodium oxalate in solution. The half equations are:

MnO4

- + 8H+ + 5e → Mn2+ + 4H2O C2O4 2- → 2CO2 + 2e

(i) Write the formula for sodium oxalate.

[1]

(ii) Suggest a structure for the oxalate ion showing all the bonds present.

(iii) Write an ionic equation for the reaction of acidified manganate (VII) with oxalate ions.

(iv) Using the ionic equation, calculate the oxidation numbers and use them to explain why the reaction is regarded as a redox reaction.

[2] [1] [3]

80

(v) Several 25.0 cm3 samples of a solution of sodium oxalate were titrated with 0.2 mol dm-3 potassium manganate (VII) solution. The average titre was 26.0 cm3. Calculate the concentration of the sodium oxalate solution in g dm-3.

(vi) What is the colour change at the end point?

[4] [1]

(vii) If an excess of sodium hydroxide is added to the titration flask after the

titration is completed, state what would be observed and write two equations for the reactions taking place.

[3]

81


2010

Chemistry


Internal Assessment

SPECIMEN PAPER

TIME

2 hours 30 minutes INSTRUCTIONS TO CANDIDATES

Write your Centre Number and Candidate Number in the spaces provided at the top of this page. Answer all three questions. Write your answers in the spaces provided. INFORMATION FOR CANDIDATES

The total mark for this paper is 70. Questions 1 and 2 are practical exercises each worth 25 marks. Question 3 is a planning exercise worth 20 marks. Quality of written communication will be assessed in Question 3. You may have access to notes, textbooks and other material to assist you. A Periodic Table of elements (including some data) is provided.

Centre number

71

Candidate number


Question Number

Marks Modera-tion Mark

1 2 3

Total Marks

82

Answer all questions. 1 A local supermarket claims their ‘own brand’ bleach gives best value for money. You

are asked to determine if this claim is valid. A solution of domestic bleach contains sodium chlorate (I), NaClO. If this solution is acidified it produces chlorine. Background information: ClO-

(aq) + 2H+

(aq) + Cl-(aq)

→ Cl2(g) + H2O(1)

The amount of chlorine which may be produced from a fixed amount of bleach is referred to as ‘available chlorine’. The amount of ‘available chlorine’ in bleach may be determined by using the bleach to liberate iodine from acidified aqueous potassium iodide. 2I-

(aq) + 2H+(aq) + ClO-

(aq) → I2(aq) + 2H2O + Cl-(aq)

The liberated iodine is then titrated with aqueous sodium thiosulphate. 2S2O3

2-(aq) + I2(aq) → S4O6

2-(aq) + 2I-

(aq) The colour of the iodine disappears at the end point. This can be made sharper by the addition of starch solution near the end point. Carry out a titration to determine the amount of ‘available chlorine’ in the supermarket’s ‘own brand’ bleach.

(a)

Method: Using a pipette filler, pipette exactly 10.0 cm3 of the bleach into a 250 cm3 volumetric flask and make it up to the mark. Transfer 25.0 cm3 of this solution to a conical flask; add 1.5 g (approximately) of potassium iodide and 20.0 cm3 dilute sulphuric acid (2 M). Swirl the mixture. Titrate the contents of the flask with standard 0.1 M sodium thiosulphate solution adding 1 cm3 of starch solution when the contents of the flask are a straw colour. Continue adding sodium thiosulphate until the colour changes from blue/black to colourless. Repeat this titration until you obtain two concordant results. Record all your results (with units) in a suitable table. Results

[12]

83

(b) (c) (d) (e)

Calculations Calculate the number of moles of sodium thiosulphate required for 25.0 cm3 of the diluted bleach. Calculate the number of moles of iodine reacting with this. Determine the number of moles of ‘available chlorine’ in 25.0 cm3 of the undiluted bleach. Calculate the number of moles of ‘available chlorine’ in the 10.0 cm3 of the diluted bleach.

[2] [2] [2] [1]

(f) Complete the following table:

Bleach Moles of ‘available

chlorine’ in 10 cm3

Cost/p Volume in bottle cm3

Own Brand

Bleach A

0.006

89 p

750

Bleach B

0.005

78 p

1000

[1]

84

(g) Evaluate which brand gives best value for money in terms of ‘available chlorine’. Is the supermarket’s claim valid?

[3]

(h) Outline two possible sources of error encountered in titration experiments and indicate how these may be minimised.

[2]

Total mark awarded

85

2 A school laboratory technician, when cleaning out the organic chemicals store, comes across five bottles of liquids from which the labels have been lost. A check of stock records indicates the bottles contained ethanal (solution), ethanol, propanone, (glacial) ethanoic acid and pentyl ethanoate. The technician randomly labels the bottles A-E. Carry out the tests given below and use the results to identify each of the liquids. As you proceed through the tests and identify a particular liquid do not carry out any further tests on it. Record, neatly and accurately, in the following table all observations including appearance of solids and solutions, colour changes, the formation and colour of precipitates, the evolution of gases, temperature changes, smells etc.

Tests 1 Cautiously smell each of the liquids A, C and E in turn by gently

wafting the vapour towards you with your hand. Record your results and interpret them as far as possible.

2 Add an equal volume of water to about 2 cm3 of each of the liquids in

turn. Shake and allow each mixture to settle. 3 To about 2 cm3 of each of the remaining liquids add, dropwise, a

solution of 2,4-dinitrophenylhydrazine (Brady’s Reagent). 4 Warm about 1 cm3 of each liquid that tested positively in 3 with

about 2 cm3 of Fehling’s solution in a hot water bath. 5 (i) To fresh 2 cm3 portions of each of the remaining liquids (in a

fume cupboard) add a small spatula measure of phosphorus (V) chloride.

(ii) Test any gas off with a drop of concentrated ammonia solution on a glass rod.

6 (i) To fresh 2 cm3 portions of the liquids tested in 5 add a spatula

measure of sodium carbonate. (ii) Test any gas evolved with a burning splint.

86

Results table Test number

Observation Conclusion

Mark available [32]

Mark awarded

87

Conclusions Identify each of the liquids A – E.

Mark available [3]

Mark awarded

Write a concise account justifying your conclusions.

Mark available [6]

Mark awarded

88

Total mark for Question 2

Max mark 45

Raw marks

Scaling × 5/9 Please record this scaled mark in the grid on the front cover of the paper.

89

3 Planning exercise Preparation of propyl benzoate, C6H5CO2CH2CH2CH3, from benzoic acid. Propyl benzoate is a liquid with a boiling point of 230oC, at normal atmospheric pressure, and has a density of 1.02 g cm-3. Like many other esters it is soluble in ethanol and insoluble in water, and may be prepared from a carboxylic acid and an alcohol. You are provided with standard laboratory apparatus and the following chemicals: Benzoic acid; white solid, soluble in ethanol, C6H5COOH Propan-1-ol; density = 0.80 g cm-3 Concentrated sulphuric acid Sodium hydrogencarbonate solution Anhydrous sodium sulphate Plan how you could prepare 50 cm3 of pure propyl benzoate based on the mass of benzoic acid used. Your plan should include: (a) the relevant equation for the esterification; (b) calculation to show the mass of benzoic acid needed assuming a 75% yield; (c) the procedure, including any relevant safety precautions; (d) how to separate and purify the propyl benzoate.

[2] [5] [6] [5]

(a)

[2]

(b)

[5]

90

(c)

[6]

(d)


[5] [2]

Mark available [20]

Mark awarded

91

Mark Schemes

92

93


2009

Chemistry


Basic Concepts in Physical and Inorganic Chemistry

SPECIMEN PAPER

MARK SCHEME

94

Section A 1 2 3 4 5 6 7 8 9 10

C B B D C B B B A D 2 marks for each correct answer

[20]

95

Section B 11 (a) (i)

Colour State at room

temperature Formula

Fluorine

Pale yellow Gas F2

(ii) the atomic radius increases as the group is descended [1] there are more completed energy levels [1]

(b) (i) F- [1]

(ii) freedom of choice [1]

[3]

[2]

[2]

12 (a) (i) hydrogen bonds [1] are present in water more energy is needed to break them [1]

(ii) higher rmm/more electrons [1] stronger van der Waal’s forces [1] (b) (i) sodium hydrogen sulphate, hydrogen iodide, iodine, sulphur

dioxide, water,

All 5 correct = 3 4 correct = 2 3 correct = 1

(ii) use a fume cupboard due to sulphur dioxide and hydrogen

sulphide [1] gloves due to corrosive conc. sulphuric acid [1]

[2] [2] [3] [2]

13 (a) Na 1s2 2s2 2p6 3s1 Na+ 1s2 2s2 2p6 Cl 1s2 2s2 2p6 3s2 3p5 Cl- 1s2 2s2 2p6 3s2 3p6

Na atom, ion and charge = [2] each error [–1] Cl atom ion and charge = [2] each error [–1] (b) energy from flame exites electron to a higher energy level [1]

electron falls to lower energy level [1] emits energy of light of specific frequency [1]

[4] [3]

(c) (i) H2SO4 + NaCl → NaHSO4 + HCl (ii) moles HCl = 19.6/36.5 = 0.54 in 250 cm3 conc = 0.54 × 4 = 2.16 mol/dm3

[1] [2]

96

(d) (i) beryllium chloride contains a covalent bond not an ionic one

(ii) beryllium chloride, chlorine monofluoride, chlorine trifluoride (iii) greater number of polar bonds and greater van der Waals

(iv) ionic forces of attraction very strong

[1] [1] [1] [1]

14 (a) (i) 1s2 2s2 2p6 3s2 3p6 3d3 4s2 (ii) d (iii) delocalised electrons [1] lattice of positive ions [1] Movement of electrons carries charge [1] (b) 46 × 8.02 + 47 × 7.31 + 48 × 73.81 + 49 × 5.54 + 50 × 5.32 368.92 + 343.57 + 3542.88 + 271.46 + 266.00 4792.83/100 = 47.93 Each error [–1] (c) 48 48 26 all 3 correct = [2] only 2 correct = [1] (d) (i) Mg 0 → +2 [1] Ti +4 → 0 [1] magnesium oxidised, titanium ions reduced [1]

[1] [1] [3] [3] [2] [3]

(ii) moles magnesium = 1500 × 103/24 = 62.5 ×103 [1] moles titanium chloride = 3800 × 10-3/190 = 20 × 103 [1] Ratio 2 : 1 so magnesium in excess [1] Moles Ti = 20 ×103 Mass Ti = 20 ×103 × 48 = 960 kg [1]

[4]

(e) (i) ability of an atom to attract [1] bonding electrons [1] (ii) Ti∂+ Cl ∂- (iii) dipoles cancel (f) MnO-

4 + 8H+ + 5 Ti3+ → 5 Ti4+ + Mn2+ + 4 H2O

[2] [1] [1] [2]

97

15 (a) (i) shared [1] pair of electrons [1] (ii)

overlap correct = [1] outer shells correct = [1] (iii) [1] pyramidal [1] (b) (i) NH3 + HCl → NH4Cl

(ii) Name coordinate [1] Explanation both electrons from same parent atom [1]

[2] [2] [2] [1] [2]

16 (a) pipette 25.0 cm3 of H2X into conical [1] add few drops of phenolphthalein [1] colourless [1] titrate until end point is reached and indicator turns pink [1] dropwise at endpoint [1] repeat until 2 accurate titres recorded +/- 0.1 [1] maximum

[6]

Quality of Written Communication 2 marks The candidate expresses ideas clearly and fluently, through well-linked sentences and paragraphs. Arguments are generally relevant and well structured. There are few errors of grammar, punctuation and spelling. 1 mark The candidate expresses ideas clearly, if not always fluently. Arguments may sometimes stray from the point. There are some errors in grammar, punctuation and spelling, but not such as to suggest a weakness in these areas. 0 marks The candidate expresses ideas satisfactorily, but without precision. Arguments may be of doubtful relevance or obscurely presented. Errors in grammar, punctuation and spelling are sufficiently intrusive to disrupt the understanding of the passage.

[2]

H H

N

H

98

(b) (i) moles = 12.5 × 0.2 /1000 = 0.0025 [1] (ii) divide by 2 = 0.00125 [1]

(iii) 0.00125 × 1000/25 = 0.05 [1]

(iv) 2.25 g in 500 cm3 4.5 g/dm3 [1]

(v) 4.5/0.05 = 90 [1]

X is Sr [1]

(c) (i) 6.30/0.05 = 126 [1]

(ii) 26 = 90 + y18 Y = 2 [1]

(iii) heat in evaporating basin [1] To constant mass [1]

[1]

[1]

[1]

[1]

[2]

[1]

[1]

[2]

99


2009

Chemistry


Further Organic, Physical and Inorganic Chemistry and Introduction to Organic Chemistry

SPECIMEN PAPER

MARK SCHEME

100

Section A 1 C

2

B

3

B

4

D

5

B

6

D

7 A

8

D

9

B

10

D

2 marks for each correct answer [20]

101

Section B 11 (a) N2 + 3H2 2 NH3

[2]

(b) iron

(c) pressure: fewer moles on RHS [1] forward reaction favoured [1] temperature: low temperature too slow [1], moderate temperature increases rate [1]

(d) glass rod dipped in conc. HCl white smoke/fumes

[1] [4] [1] [1]

12

(a) CH3 CH3 CH3 – C – CH2 – CH – CH3 CH3 (b) (i) C8 H18

(ii) C4 H9

(c) (i) carbon, carbon monoxide, water (ii) carbon dioxide, water

[2] [1] [1] [2] [2]

(d) distance between particles less greater frequency of collisions

(e) C8H18 = 96 + 18 = 114

114101 3−×

= 8.77 × 10-6 mol

8 mol CO2 formed 8 × 8.77 × 10-6 = 7 × 10-5 mol 7 × 10-5 × 24000 = 1.68 cm3

[1] [1] [4]

(f) (i) Pd or Rh

(ii) forms CO2 (iii) catalyst (solid) and gases not in same state

[1] [1] [1]

102

13 (a) (i) C4H9OH + HBr → C4H9Br +H2O

(ii) evaporate/boil allow vapours to condense and return to flask

[2] [1] [1]

(b) carbon dioxide formed invert separating funnel open tap

[1] [1] [1]

(c) anhydrous sodium sulphate/magnesium sulphate/calcium chloride

[1] [1]

(d) C4H9OH = 74

moles C4H9OH 7411 = 0.15

moles C4H9Br = 0.15 mass C4H9Br = 0.15 × 137 = 20.55

% yield 55.205.12 = 60.9%

[3]

(e) (i) nucleophilic substitution

(ii)

H C3H7 H C3H7 – C – Br → HO - - - C - - - Br → C3H7 – C – OH + Br- OH- H H H H

[1] [1] [3]

(f) (i) elimination

(ii) but-1-ene or CH3CH2CH = CH2

[1] [1]

103

14 (a) outer (electron) is in an s shell

(b) (i) radius increases as number of shells increases

(ii) decreases outer electron further from the nucleus increased shielding (by inner electrons)

[1] [1] [1] [1] [1] [1]

(c) combustion : flame colour [1] white solid formed by both [1]

reaction with water : Ca – fizzes [1] Mg – very slow reaction / reacts with steam [1] Ca – exothermic [1] Ca – white solid forms [1] to maximum of 2 reaction with acid : both fizz [1] both dissolve [1] both exothermic [1] to maximum of 2


[2] [2] [2]

[2]

104

(d) (i) ability to neutralise an acid/proton acceptor

(ii) CaO + H2O → Ca(OH)2 (iii) 0.021 × 74 = 1.55 g mass in 250 cm3 = 0.39 g

(e) Ca(OH)2 + 2HCl → CaCl2 + 2H2O

[1] [1] [3] [2]

15 (a) enthalpy

[3]

(b) ΔH = 100 × 4.2 × 20.5 = 8610 J moles C2H5OH = 0.4 = 0.0087 mol 46 0.0087 mol gives 8.61 kJ 1 mol gives 989.7 kJ

[4]

(c) bonds broken

5 C – H = 5 × 413 = 2065 1 C – C = 1 × 347 = 347 1 C – O = 1 × 358 = 358 1 O – H = 1 × 464 = 464 3 O = O = 3 × 498 = 1494 Total = 4728 [1]

bonds formed 4 C = O = 4 × 805 = 3220 6 O – H = 6 × 464 = 2784 Total = 6004 [1] enthalpy change = 4728 – 6004 = –1276 kJ

[4]

Ethanol + oxygen

Carbon dioxide + water

105

(d) CH3OH = 32 C2H5OH = 46 32 g of methanol produces 726 kJ 1 g of methanol produces 22.7 kJ 46 g of ethanol produces 1367 kJ 1 g of ethanol produces 29.7 kJ ethanol produces most energy

[3]

106

107


2009

Chemistry


Internal Assessment

SPECIMEN PAPER

MARK SCHEME

108

see notes below

Section A 1 Titration Exercise

(a) Procedure

• Rinse out a pipette with the standard sulphuric acid solution • Using the pipette and a pipette filler, place 25.0 cm3 of the standard sulphuric acid

solution in the conical flask [1] • Rinse out the burette with the metal hydroxide solution Fill the burette with the metal hydroxide solution [1] • Add 2 or 3 drops of phenolphthalein to the conical flask and then add the metal hydroxide solution until the end point is reached [1] • Record the results of the one rough and two accurate titrations in the table [1] [4]

(b) Results

Initial burette reading/cm3

Final burette reading/cm3

Titre/cm3

rough 1st accurate 2nd accurate

Average titre cm3 (The supervisor’s titration value should be recorded in red ink beside the candidates’ average titre) Marks awarded Acceptable labelled table (1) (example above) Significant figures (max 2) Titration consistency (max 3) Agreement with supervisor’s titre (max 4) Calculation of average titre (max 2)

[12]

109

NOTES Results

Clearly labelled and neatly presented table, including units and the recording of the average titre. [1] Significant figures All accurate titration readings recorded to one decimal place (including initial burette reading ie 0.0 if used). Accept however, 0.00 and 0.05 but penalise by [-1] if other readings are given to two or more decimal places. The use of 0 is penalised by [-1] if used (only penalise once). [2]

Titration consistency This is the difference between the accurate readings: Difference Mark ± 0.1 3 ± 0.2 2 ± 0.3 1 ≥ 0.4 0 [3]

Agreement with supervisors’ average time Difference Mark ± 0.1 4 ± 0.2 3 ± 0.3 2 ± 0.4 1 ≥ 0.5 0 [4]

Average titre Using only accurate titres [2]. The inclusion of the rough titre in this calculation is penalised by [-1]. The average titre can be to two decimal places eg 21.33. An incorrect calculation is 0 but this error must be carried through to other calculations, if appropriate. [2]

(c) Indicator changes from colourless to pink [1] (d) Relevant equation: H2SO4 + 2MOH → M2SO4 + 2H2O [2]

110

(e) Calculations

no. of moles H2SO4 = 1000

05.00.25 × = 0.00125

[1]

moles of MOH = moles of H2SO4 × 2 = 0.00125 × 2 = 0.0025

[1]

∴(average titre) cm3 of MOH contains 0.0025 moles

1 dm3 of MOH contains titreAverage10000025.0 ×

NB Average titre should be 18.8 cm3

∴concentration of MOH = 8.1810000025.0 × = 0.133 mol dm-3

RMM = 3dm1inMol

3dm1inmass = 133.033.5 = 40.08

[1]

RAM = 40.08 – 17 = 23.08

[1]

(f) Conclusion

M is sodium [1]

111

2 Observation and Deduction Mark Scheme (a)

Experiment


(i) Describe A

White solid [1]

Transition metal absent/ Group I or II metal compound/ NH +

4 / s-block compound [1]

(ii) Fill a test tube full of water and record the temperature.

Add three spatula measures of A to the test tube, stir and note the temperature.

Dissolves/colourless solution [1] Temperature drop/ temperature values given [1]

Soluble/ionic [1] Endothermic [1]

(iii) Add 3 drops of the solution formed in (ii) to another test tube.

Acidify with 3 drops of dilute nitric acid and then add 1 cm3 of silver nitrate solution.

Add 5 cm3 of dilute ammonia solution to the test tube.

White precipitate [1] Dissolves/colourless solution [1]

Chloride present [1] Complex formed [1]

(iv) Add a spatula measure of A to a test tube one third full of dilute sodium hydroxide solution and warm gently, testing any gas evolved with moist pH paper.

Effervescence [1] Dissolves/colourless solution [1] Smell [pungent] [1] Turns blue/ pH >7 [1]

Alkaline [1] Ammonia/ NH +

4 [1]

A is Ammonium chloride/NH4Cl [1]

112

(b)

Experiment Observations Deductions

(i) Describe the smell of solution B

Description of smell [1] Organic/carboxylic acid/ethanoic acid [1]

(ii) Using a glass rod place a drop of B onto pH paper

Turns orange/red/ pH = 2-5 [1]

Acid/carboxylic acid/ethanoic acid [1]

(iii) Add a spatula measure of anhydrous sodium carbonate to a test tube one quarter full of solution B and identify the gas evolved using a suitable reagent.

Effervescence [1] Dissolves/colourless solution [1] Limewater turns milky [1]

Acid/neutralisation reaction/appropriate equation [1] CO2 evolved [1]

(iv) Add 1 cm3 of B to a test tube. Add a 2 cm length of

magnesium ribbon.

Effervescence [1] Dissolves/colourless solution [1] Heat evolved [1]

Acid/equation [1] Hydrogen evolved [1]

B is: a carboxylic acid/ethanoic acid/ CH3COOH [1] Question 2 has 32 marking points. Mark to a maximum of 29.

113

Section B 3 (a) (i) diagram of crucible, tripod, Bunsen burner

(ii) avoid touching hot apparatus/gloves/ allow to cool

(b) (i) weigh crucible empty and with Group II carbonate

(ii) heat, weigh, repeat until two readings the same (c) (i) subtract/2.57

(ii) divided by 44/0.058

(iii) 0.058

(iv) 0.058 = 2.33 (x + 16)

= 24

(v) M = Mg

[3] [1] [1] [2] [1] [1] [1] [1] [1]

(d) (i) limewater [1] turns milky [1]

(ii) Ca(OH)2 + CO2 → CaCO3 + H2O (e) (i) MCO3 + 2HCl → MCl2 + H2O + CO2

(ii) concentration is known (iii) phenolphthalein/methyl orange

[2] [2] [2] [1] [1]

Questions 4-11 have 2 marks for each correct answer

4 B

5 B

6 B

7 A

8 D

9 D

10 C

11 A [16]

114

115


2010

Chemistry


Periodic Trends and Further Organic, Physical and Inorganic Chemistry

SPECIMEN PAPER

MARK SCHEME

116

Section A 1 D

2

C

3

B

4

C

5

C

6

C

7

C

8

B

9

C

10

B 2 marks for each correct answer

[20]

117

Section B 11 (a) rotates the plane [1]

of plane polarised light [1]

(b) one for each correct 3D structure [2] shown in 2D = [2] correct connectivity [1]

[2]

[3]

12 (a) K+ (g) + ½Cl2 (g) + e− [1] K (g) + ½Cl2 (g) [1] (b) X = 90 + 418 + 121 – 348 – 701 = −420 kJ mol−1

Each error [-1]

[2] [2]

13 (a) (i) ΔH = Σ ΔHf (products) − Σ ΔHf (reactants) = [(−635) + (−394)] − [(−1207)] = 178 kJ mol−1

equation or equivalent = [1] correct value and units = [1]

(ii) ΔS = Σ S (products) − Σ S (reactants) = [(40) + (214)] − [(90)] = 164 J K−1 mol−1

equation or equivalent = [1] correct value and units = [1]

(b) ΔG = ΔH − TΔS ΔG = 178 − (298 × 0.164) = +129 kJ mol−1 since ΔG is positive reaction is not feasible equation = [1] correct value and units = [1] appropriate statement = [1]

(c) reaction becomes feasible when ΔG changes from positive to negative ie when ΔG = 0.

if ΔG = ΔH − TΔS ΔG = 0 when ΔH = TΔS ∴ T = ΔH ÷ ΔS

T = (178) ÷ (0.164) = 1085K equation = [1] consistency with units = [1] correct value and unit = [1]

[2] [2] [3] [3]

118

14 (a) 1-bromo-2,2-dimethylpropane (b) (i) 1 (ii) 1 (iii) Rate = k [neopentyl bromide] [OH−] (iv) 0.68 = k × 0.02 × 0.01 0.68 = k × 0.0002 k = (0.68) ÷ (0.0002) = 3400 mol−1 dm3 s−1

value = 1 Units =1 (v) flow scheme for SN2

Dipole +1, Nucleophilic attack = 1, Structure of T.State =1

[2] [1] [1] [1] [2] [3]

15 (a) * concentration of hydrogen decreases [1] there are more molecules on the r.h.s. [1] * –essential

[2]

(b) CH4(g) + H2O(g) → CO(g) + 3H2(g)

mol. initially 7.5 mol 6.0 mol 0.0 mol 0.0 mol mol. at equm 2.0 mol 0.5 mol 5.5 mol 16.5 mol total number of moles = 24.5 moles mole fraction =

5.240.2

5.24

5.0

5.245.5

5.245.16

= 0.082 0.020 0.255 0.673

partial pressure (atm)

= 20.4 atm

5.1 atm

56.1 atm

168.4 atm

KP =

))g(OH(p))g(CH(P))g(H(P))g(CO(P

24

23

= 1.54.20

)4.168(1.56 3

××

= 2.58 × 106 [1] atm2 [1]

[4]

119

16 (a) (i) OH– + H+ → H2O (ii) the solution is equivalent to 5 cm3 of 0.1 M acid in 45 cm3 moles of H+ = 5 × 10–3 × 0.1 = 5 × 10–4 mol [H+] = 5 × 10–4 in 45 cm3

= 45

10105 34 ×× −

= 1.1 × 10–2 mol dm–3 pH = 1.96

[1] [3]

(b) (i) NH3 + H+ → NH4+

(ii) methyl orange (iii) methyl orange changes colour at an acidic pH [1] vertical section of curve in acidic region [1]

[1] [1] [2]

(c) ammonium ions remove hydroxide ions leaving hydrogen ions [1] weak base reacted with strong acid [1]

[2]

(d) (i) use of results to obtain equivalence point of 11.8 cm3 [1] moles of NaOH added = 0.1 × 0.118 = 0.00118 [1] CH3COOH and NaOH react in a 1 : 1 ratio [1] moles of CH3COOH = 0.00118 [1] [CH3COOH] = 0.00118 ÷ 0.025 = 0.0472 mol dm–3 [1]

[5]

(ii) [Butanoic Acid] = [Sodium Butanoate] [2] buffer solution therefore pH = pKa [1] Ka = 10–4.82 = 1.51 × 10–5 mol dm–3 [2]

[5]

17

(a) O ║ CH3CCH3 (b) CH3COCH3 + H2NNH – C6H4(NO2) 2 → (CH3)2C = NNH – C6H4(NO2)2 + H2O (c) yellow-orange precipitate [1] (d) melt it [1] compare with tables of melting points of 2, 4-dinitrophenylhydrazone derivatives [1]

[1] [2] [1] [2]

120

18

(a) COOH CH3CH2 – *C – CH3 H (b) 3-methylbutanoic acid (c) (i) 2CH3(CH2)3CO2H + Na2CO3 → 2CH3(CH2)3CO2Na + H2O +CO2 (ii) add hydrochloric acid/sulphuric acid/mineral acid

[2] [2] [2] [1]

(d) C5H10O2 = 102 mass = 5 × 10–6 × 103 × 0.95 = 4.75 × 10–3 g RMM; C5H10O2 = 60 + 10 + 32 = 102

moles = 102

1075.4 3−× = 4.66 × 10-5 mol

concentration = 3

5

dm89mol1066.4 −× = 5.8 × 10–7 mol dm–3

[3]

(e) (i) CH3(CH2)3CO2H + C2H5OH → CH3(CH2)3CO2C2H5 + H2O (ii) heat/concentration/sulphuric acid or hydrochloric acid

[2] [2]

19 (a) glycerol/propane-1,2,3-triol (b) many double bonds (c) add Wijs reagent and keep in dark for 30 mins [1] add potassium iodide [1] titrate with sodium thiosulphate [1] starch indicator [1] until blue-black colour disappears [1] blank titration [1] to be a maximum of [5] Quality of written communication

[1] [1] [5] [2]

121


(d) (i) milligrams of KOH [1] required to saponify 1 gram of fat [1]

or

saponification value = fatofgrams

KOHofmgs

(ii) mole of KOH added = 0.125 × 0.04 = 0.005 moles

mole of HCI = 0.125 × 0.023 = 0.00288 moles [1] moles of KOH used = 0.0021 moles [1] mass of KOH = moles × RMM = 0.021 × 56 = 0.118 g = 118 mg [1]

saponification value = 1488.0

118= [1]

(e) hardening (of oils)/hydrogenation

[2] [4] [1]

122

20 (a) Na2O + H2O → 2NaOH or O2- + H2O → 2OH (b) (i) (an oxide which) reacts with an acid and a base behaves as (ii) Al2O3 + 2NaOH + 3H2O → 2NaAl(OH)4 or Al2O3 + 2NaOH → 2NaAlO4 + H2O or Al2O3 + 2OH– + 3H2O → 2Al(OH)4

–

[2] [1] [2]

(c) (i) Cl Cl Cl Al Al Cl Cl Cl (ii) Al2O6 + 6H2O → Al2O3 + 6HCI or Al2O6 + 3H2O → Al2O3 + 6HCI or Al2O6 + 12H2O → 2(Al(H2O)6) 3+ Cl3

[2] [2]

123


2010

Chemistry


Analytical, Transition Metals, Electrochemistry and Further Organic Chemistry

SPECIMEN PAPER

MARK SCHEME

124

Section A

1 C

2 D

3 B

4 D

5 D

6 D

7 B

8 D

9 C

10 D

2 marks for each correct answer [20]

125

Section B 11

Ni(OH)2 Ni(NH3)6

2+ Ni(edta)2- Ni(en)3

2+

[1][1][1][1] [4]

12 (a) (i) NH3+CH2CO2-

(ii) strong attraction between the ions

(b) C6H5COCl + NH2CH2CO2H → C6H5CONHCH2CO2H + HCl

[1]

[1][1]

[2]

(c) (i) 2NH2CH2CO2H + Na2CO3 → 2NH2CH2CO2Na + H2O + CO2

(ii) NH2CH2CO2H = C2H5O2N = 75 3 g = 3/75 = 0.04 mol Na2CO3 = 106 8.4 g = 8.4/106 = 0.08 mol

2 marks for obtaining 0.08 mol hence sodium carbonate is in excess and calculation based on 0.04 mol 0.04 mol glycine gives 0.02 mol carbon dioxide 0.02 × 24 dm3 = 0.48 dm3

(d) (i) NH2CH2CO2H + CH3OH → NH2CH2CO2CH3 + H2O

(ii) esters are more volatile than the amino acids pass through GLC more quickly/do not stick

[2]

[4]

[1]

[1][1]

[14]

13 (a) boil with concentrated hydrochloric acid/alkali (b) amino acids (c) ninhydrin blue colour (d) peptide/protein (enzyme is incorrect) (e) spot a concentrated sample on paper

run in named first solvent turn 90 and run in second named solvent spray with ninhydrin

(f) distance travelled by solute relative to solvent

or distance travelled by solute distance travelled by solvent

[1][1]

[1]

[1][1]

[1]

[1][1][1][1]

[1]

[11]

126

14 (a) (i) more molecules on the RHS low pressure

(ii) fractional distillation

(b) (i) this is the methyl group next to the carbonyl

(ii) must be next to an alkyl group/methylene (iii) must be next to a CH2 (iv) ratio is 2:3:3 the CH3 next to CH2 should be at highest ppm or the integration curve should be in the order 2, 3, 3 (v) the TMS signal is well away from the rest of the signals it is unreactive

(c) 29 CH3CH2

+ 43 CH3CO+ (d) samples of the equilibrium mixture taken passed through GLC giving two peaks/retention times the area under the peaks gives ratio of butanone to butanol

[1][1]

[2]

[1]

[1]

[1]

[1]

[1]

[1] [1]

[1] [1]

[1][1][1]

[16]

15 (a) incomplete d-shell variable oxidation state

catalytic activity coloured complexes 1 each to a maximum of [3]

(b) 1s2 2s2 2p6 3s2 3p6 3d3 4s2 (c) (i) V2O5

(ii) catalyst in the manufacture of sulphuric acid

(d) (i) VO2

+ VO2+ V3+ V2+ yellow blue green violet explanation based on the “anticlockwise rule” or individual cells formed

(ii) yes identify the equations involved, manganate to the RHS and V3+ to the LHS

(iii) MnO4

- + 5VO2+ + H2O → Mn2+ + 2H+ + 5VO2+

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(e) explanation of active site lock and key mechanism lower activation energy explanation of effect of pH explanation of temperature

[1][1][1][1][1]

[18]

16 (a) extensive delocalisation of the overlapping p orbitals molecular energy levels are close together electrons raised to a higher level by light colours apart from red and orange removed from white light to leave red + orange 1 each to a maximum of [4] Quality of written communication

[4]

[2]


(b) carotene is not polar

like dissolves like/fats contain large alkyl chains

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128

(c) (i) 103 cm3 of hydrogen = 103/24000 = 0.00429 mol

C7H8 = 84 + 8 = 92 0.129g = 0.129/92 = 0.00140 mol 1 mol of hydrocarbon reacts with 3.06 mol of hydrogen 3 double bonds present

(ii) nickel molecules brought closer together activation energy lowered bonds weakened or broken

(d) benzene delocalised system stable alkenes sigma and pi bond which is easily broken

[3]

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[2][2]

[19]

17 (a) 6H+ + MnO4- + 5NO2

- → 2Mn2+ + 3H2O + 5NO3-

(b) (i) Na2C2O4

(ii) -O O- O=C-C=O allow 1 mark for partial sucess

(iii) 16H+ + 2MnO4- + 5C2O4

2- → 2Mn2+ + 8H2O + 10CO2

(iv) reactant +7 +3 products: +2 +4 explanation ie manganese oxidation number goes down and carbon goes up

(v) moles of manganate (VII) = 26.0 × 10-3 × 0.2 = 0.52 × 10-2 moles of sodium oxalate = 2.5 × 0.52 × 10-2 = 0.013 mol in

25 cm3 = 0.52 mol in 1 dm3 sodium oxalate = 46 + 24 + 64 = 134 0.52 mol of sodium oxalate = 0.52 × 134 = 69.68 g

(vi) pink to colourless

(vii) white precipitate darkens in air

H+ + OH- → H2O Mn2+ + 2OH- → Mn(OH)2

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2010

Chemistry


Internal Assessment

SPECIMEN PAPER

MARK SCHEME

130

1 (a) Results

Clearly labelled and neatly presented table, including units and the recording of the average titre. Significant figures: All accurate titration readings recorded to one decimal place (including initial burette reading a 0.0 if used). Accept, however, 0.00 and 0.05 but penalise by [-1] if other readings are given to two or more decimal places. The use of 0 is penalised by [-1] if used (only penalise once). Titration consistency: This is the difference between the accurate readings. Difference Mark ± 0.1 3 ± 0.2 2 ± 0.3 1 > 0.4 0

[1] [2]

[3]

Agreement with supervisor’s average titre (The supervisor’s titration value should be recorded in red ink beside the candidates’ average titre) Difference Mark ± 0.1 4 ± 0.2 3 ± 0.3 2 ± 0.4 1 > 0.5 0 Average titre: the inclusion of the rough titre in this calculation is penalised by [-1]. The average titre can be to two decimal places eg 21.33. An incorrect calculation is 0 but this error must be carried through to other calculations, if appropriate. Calculations

[4] [2]

(b) no. of moles of sodium thiosulphate required. (c) moles of iodine reacting with this. (d) no. of moles of ‘available chlorine’ in diluted bleach (e) no. of moles of ‘available chorine’ in undiluted sample (f) completion of the table. (g) evaluation (h) sources of error

[2] [2] [2] [1] [1] [3] [2]

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2

Maximum mark = 32

Test Observations Conclusions 1 A sweet smell/pear drops [1] Possibly pentyl ethanoate [1] C pleasant/alcohol like [1] Possibly ethanol [1] E sharp/acrid/like vinegar [1] Possibly ethanoic acid [1] 2 A two layers form/immiscible [1] A is pentyl ethanoate [1] B-E soluble/solution formed/

miscible [1]

3 B orange precipitate [1] Possibly ethanal or propanone [1] C no precipitate [1] Possibly ethanol or ethanoic acid [1] D orange precipitate [1] Possibly ethanal or propanone [1] E no precipitate [1] Possibly ethanol or ethanoic acid [1] 4 B solution remains blue/

no change [1] B is propanone [1]

D red/brown precipitate [1] D is ethanal [1] 5(i) C – vigorous reaction/

exothermic [1] Contains OH group [1]

E vigorous reactions/ exothermic [1]

Contains OH group [1]

(ii) White [1] fumes/smoke/solid [1] Gas is hydrogen chloride [1] 6(i) C – no reaction [1] C is ethanol [1]

E effervescence [1] (ii) Gas extinguishes burning splint [1] E is ethanoic acid [1]

Conclusions correct identification A penthyl ethanoate B propanone C ethanol D ethanal E ethanoic acid correct list [3] two incorrect [2] more than two incorrect [0]

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Justification statement A is pentyl ethanoate as esters have a sweet smell and it is insoluble in

water while others are all soluble B is propanone as it gives an orange precipitate with Brady’s reagent/test

but has no reaction with Fehling’s solution/test 4 C is ethanol as test 5 shows it contains an –OH group but test 6 shows no

reaction with sodium carbonate

[2] [2] [2]

D is ethanal as it gives an orange precipitate with Brady’s reagent/test 3

and a red/brown precipitate with Fehling’s solution/test 4 E is ethanoic acid as test 5 shows it contains an – OH group and it

evolves, possibly CO2 with sodium carbonate

Maximum marks = 45 Scale to 25 Raw mark ×95 =

This scaled mark is recorded on the front cover of the candidate’s script

[2] [2]

3 (a) C6H5COOH + C3H7OH → C3H7OCO C6H5 + H2O (H2O missing [-1])

(b) 50cm3 of propyl benzoate = 50 × 1.02 = 51.0 g

propyl benzoate = C10H12O2 = 164

number of mols of propyl benzozate = 164

0.51 = 0.31 mol

benzoic acid = C7H6O2 = 122 0.31 mol benzoic acid = 0.31 × 122 = 37.82 g this assumes 100% hence more needed for a 75% yield

ie 34 × 37.82 = 50.43 g

[2] [5]

(c) place (the benzoic acid and propan-1-ol) in a flask add the conc. Sulphuric acid dropwise/slowly/with stirring add anti-bump granules reflux safety glasses/gloves (must be linked to using conc. Acid)

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(d) initial distillation, wash with sodium hydrogencarbonate solution provided, separate organic layer, dry with anhydrous sodium sulphate provided, final distillation.


2 marks The candidate expresses ideas clearly and fluently, through well-linked sentences and paragraphs. Arguments are generally relevant and well structured. There are few errors of grammar, punctuation and spelling.

[1] [1] [1] [1] [1] [2]

1 mark The candidate expresses ideas clearly, if not always fluently. Arguments may sometimes stray from the point. There are some errors in grammar, punctuation and spelling, but not such as to suggest a weakness in these areas. 0 marks

The candidate expresses ideas satisfactorily, but without precision. Arguments may be of doubtful relevance or obscurely presented. Errors in grammar, punctuation and spelling are sufficiently intrusive to disrupt the understanding of the passage.

Maximum mark available

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135

136

137

Documents

AS & A2 Chemistry