1.

Write the formula and charge of the ion which forms when ammonia, NH3, accepts a proton. ........................................................................................................................................ ......(1)

2.

(a) An aqueous solution of silver nitrate is added to an aqueous solution of potassium iodide in a test-tube. (i) State what you would observe. ................................................................................................................... .......(2)

(ii)

Write a balanced equation including state symbols for the reaction that occurs. ................................................................................................................... .......(2)

(b)

The reaction in (a) is repeated using potassium bromide instead of potassium iodide. The reaction mixture is allowed to stand in sunlight for a few minutes. (i) State what you would observe after a few minutes. ................................................................................................................... .......(1)

(ii)

Suggest a useful application of this reaction. ................................................................................................................... .......(1)

(iii)

Concentrated ammonia solution is added to the reaction mixture in (b). State and explain what you would observe. Observation................................................................................................ ....... ................................................................................................................... ....... Explanation................................................................................................

........ ................................................................................................................... .......(1)

(c)

A few drops of concentrated sulphuric acid are added to some potassium bromide in a test-tube. At first a gas is given off which fumes at the mouth of the test-tube and gives dense white fumes with ammonia. (i) Name the gas given off. ................................................................................................................... .......(1)

(ii)

Write a balanced equation for the reaction between the gas and ammonia. ................................................................................................................... .......(1)

(iii)

After a short time reddishbrown fumes are observed in the test tube. Name this gas. ................................................................................................................... .......(1)

(iv)

During this time a piece of filter paper soaked in acidified potassium dichromate(VI) is held at the end of the test-tube. The colour changes from yellow to green. Name the gas which produces this change. ................................................................................................................... .......(1)

(v)

Concentrated sulphuric acid has reacted in two ways in these reactions. Classify its behaviour. In reaction (c) (i) ................................................................................................. In reaction (c) (iii) ...............................................................................................(2) (Total 14 marks)

3.

(a) An aqueous solution of silver nitrate is added to an aqueous solution of potassium iodide in a test-tube. (i) State what you would observe. ................................................................................................................... .......(2)

(ii)

Write a balanced equation including state symbols for the reaction that occurs. ...................................................................................................................

.......(2)

(b)

The reaction in (a) is repeated using potassium bromide instead of potassium iodide. The reaction mixture is allowed to stand in sunlight for a few minutes. (i) State what you would observe after a few minutes. ................................................................................................................... .......(1)

(ii)

Suggest a useful application of this reaction. ................................................................................................................... .......(1)

(iii)

Concentrated ammonia solution is added to the reaction mixture in (b). State and explain what you would observe. Observation................................................................................................ ....... ................................................................................................................... ....... Explanation................................................................................................ ........ ................................................................................................................... .......(1)

4.

A few drops of concentrated sulphuric acid are added to some potassium bromide in a test-tube. At first a gas is given off which fumes at the mouth of the test-tube and gives dense white fumes with ammonia. (i) Name the gas given off. .................................................................................................................. .......(1)

(ii)

Write a balanced equation for the reaction between the gas and ammonia. .................................................................................................................. .......(1)

(iii)

After a short time reddishbrown fumes are observed in the test tube. Name this gas. .................................................................................................................. .......(1)

(iv)

During this time a piece of filter paper soaked in acidified potassium dichromate(VI) is held at the end of the test-tube. The colour changes from yellow to green. Name the gas which produces this change. ..................................................................................................................

.......(1)

(v)

Concentrated sulphuric acid has reacted in two ways in these reactions. Classify its behaviour. In reaction (c)(i) .................................................................................. .............. In reaction (c)(iii) ............................................................................................. .(2) (Total 14 marks)

5.

(a) Chloroethene, C2H3C1, is the monomer from which the important plastic poly(chloroethene) is made. It is often known as PVC. It can be produced with any degree of flexibility from rigid to pliable. (i) Draw the displayed formula of chloroethene.

(1)

(ii)

Draw a dotandcross diagram of a chloroethene molecule. You need include only outer shell electrons.

(2)

(b)

Use the Hess cycle and the data, at 298 K, to calculate the standard enthalpy change of formation of chloroethene.

H

c

[C 2 H 3 C l(g )] H f [H 2 O (l)] H f [C O 2 (g )]c

= 1 2 6 4 k j m o l 1 = 2 8 6 k j m o l 1 = 3 9 4 k j m o l 1 2 C O 2 (g ) +3 2

C 2 H 3 C l( g ) +

11 4

O 2(g )

H

[ C 2 H 3 C l]

H 2 O ( l) +

1 2

C l 2 (g )

H

f

[C 2 H 3 C l] 2 C (g ra p h ite ) +3 2

H 2(g ) +

1 2

C l2 (g ) +

11 4

O 2 (g )

(3)

(c)

A possible route for making chloroethene in the laboratory is as follows: C 2H S te p 14

C 2 H 4 C l2

S te p 2

C 2H 3C l c h lo ro e th e n e

e th e n e

1 ,2 d ic h lo r o e th a n e

Suggest reagents and conditions for each step. Step 1 ................................................................................................................ ......... .............................................................................................................................. ...... Step 2 ................................................................................................................ ......... .............................................................................................................................. ......(4)

(d)

(i) Write a balanced equation for the formation of poly(chloroethene) from chloroethene. ................................................................................................................... .......(1)

(ii)

Suggest appropriate conditions for the polymerization reaction. ................................................................................................................... ....... ................................................................................................................... .......(2)

(iii)

State the type of polymerization reaction involved in the formation of poly(chloroethene). ................................................................................................................... .......(1)

(iv)

Suggest a use for poly(chloroethene), explaining why it is suitable. ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(1)

(Total 15 marks)

6.

Chloroethene, C2H3C1, is the monomer from which the important plastic poly(chloroethene) is made. It is often known as PVC. It can be produced with any degree of flexibility from rigid to pliable. (i) Draw the displayed formula of chloroethene.

(1)

(ii)

Draw a dotandcross diagram of a chloroethene molecule. You need include only outer shell electrons.

(2)

7.

A possible route for making chloroethene in the laboratory is as follows: C 2H S te p 14

C 2 H 4 C l2

S te p 2

C 2H 3C l c h lo ro e th e n e

e th e n e

1 ,2 d ic h lo r o e th a n e

Suggest reagents and conditions for each step. Step 1 ...................................................................... ................................................. ..................... .................................................................................................. Step 2 ....................................................................................................................... . .. ...................................................................................................................... ...(4)

8.

(i) Write a balanced equation for the formation of poly(chloroethene) from chloroethene. .. ............................................................................................................... ...(1)

(ii)

Suggest appropriate conditions for the polymerization reaction. .. ............................................................................................................... ... ..

............................................................................................................... ...(2)

(iii)

State the type of polymerization reaction involved in the formation of poly(chloroethene). .. ............................................................................................................... ...(1)

(iv)

Suggest a use for poly(chloroethene), explaining why it is suitable. .. ............................................................................................................... ... .. ............................................................................................................... ... .. ............................................................................................................... ...(1) (Total 15 marks)

9.

Read the passage on petroleum refining straight through, and then more carefully, in order to answer the following questions. (a) Petrol produced by simple crude oil distillation has a low octane rating and is not suitable for modern car engines. (i) What technological change led to the need for higher octane rating fuels?(1)

(ii) (b)

What is the effect of using a low octane fuel in a modern petrol engine?(1)

CH3CH2CH2CH2CH2 CH2 CH2 CH3

B enzene C H3

M e th y lb e n z e n e CH3C(CH3)2C(CH3)2CH3 2,2,3,3Tetramethylbutane

(i)

Name the two chemicals from the four hydrocarbons above which are isomers of each other.(1)

(ii)

Name the hydrocarbon with the lowest spontaneous ignition temperature.(1)

(c)

(i) How has the cost of producing petrol been affected by the reduction in permitted lead content?(1)

(ii) (d)

Why have limits been placed on the maximum concentration of benzene in petrol?(1)

Write a summary in continuous prose, in no more than 100 words, of the chemical processes involved in the manufacture of petrol today. You are not asked to summarise the whole passage, nor to include equations in your summary. At the end of your summary state the number of words you have used.(9)

Credit will be given for answer written in good English, using complete sentences and with correct use of technical words. Avoid copying long sections from the original text. Numbers count as one word, as do standard abbreviations and hyphenated words. Any title you give to your passage does not count in your word total. There are penalties for the use of words in excess of 100.(Total 15 marks)

Petroleum refining in the postlead era Commercial petroleum refining can be traced back to 1863 when Samuel Andrews, a candlemaker and lard oil refiner, extracted lamp oil from newly discovered reserves of crude petroleum. Lamp oil was the only petroleum product of interest in 1863, but demand for a much wider product range grew over the next 100 years from developments in transport, in power generation and the organic chemical industry. And nowadays we are aware of the toxic nature of some of the compounds in crude petroleum and petroleum products. Oil refining Today oil refineries have to provide products in the quantities and qualities required to satisfy market requirements no easy matter, considering the complex chemistry of crude oil, and a global consumption of its products exceeding 3000 million tonnes per annum. Alkanes and cycloalkanes predominate in crude oils, and alkenes exist

only in trace amounts. A single crude oil may contain upwards of 10,000 individual compounds, though this is of little significance to the refiner, whose main concern is to break down the starting materials into suitable boiling ranges. Separation by fractional distillation is the most convenient way of doing this, producing a range of products which usually require further conversion and treatment processes. In the early days of oil refining, products from fractional distillation were used with little or no further processing. This is no longer the case. Today, motor car engine compression ratios approach 10:1 compared with 4:1 in 1914, and fuel of high spontaneous ignition temperature must be used to avoid the damaging and wasteful effects of preignition (knock) and autoignition (pinking). The octane scale is used as an indication of resistance to engine knock. A high octane rating indicates good resistance modern petrols (known as gasolines in the refining industry) need ratings of between 95 and 98. Arenes and highly branched alkanes, in comparison with straight chain alkanes, have high spontaneous ignition temperatures and excellent resistance to knock. Petrol that is produced simply by crude oil distillation has an octane rating of less than 50 and requires considerable conversion to make it acceptable.

Conversion processes Here, molecular sizes and shapes are modified to provide refinery products. Cracking, both thermal and catalytic, reduces molecular size and converts heavy residues into lighter and more marketable products. Catalytic cracking is particularly attractive for petrol production. A low demand, high boiling point product of distillation is converted to a high octane fuel. The first catalytic cracking unit contained acidtreated clays, in the form of pellets, as the catalyst. Nowadays crystalline aluminosilicates known as zeolites, are used. Thermal cracking, the method of increasing petrol output in about 1914, fell out of favour with the advent of catalytic processes, but is re emerging as an important method for converting very heavy residues into petrol blendstocks. In one variant, the residues from vacuum distillation are heated to 500C for several seconds and the cracked products are distilled. About 10 percent of the feed is converted to petrol, and some gas oil suitable for catalytic cracker feedstock is produced. Catalytic reforming is used to raise the octane rating of distillates in the petrol boiling range by converting straight chain alkanes and cycloalkanes to arenes. The octane rating is increased from 50 to greater than 95. The dehydrogenation reactions taking place during reforming provide a valuable source of hydrogen for use in sulphur removal. Greater amounts of unsaturated hydrocarbons have become available in the refinery as a result of increased cracking activity. These have potential as polymer feedstocks. Treatment processes The final stage in the manufacture of petrol involves blending components from distillation, cracking and the various reforming processes to produce a fuel with the required volatility and knock resistance at minimum cost. In principle, any octane rating fuel likely to be required by the car industry can be produced in this way. However, compensation for the reduction in allowable lead alkyls tends to raise costs dramatically. Furthermore, limits have been placed on the maximum concentration of benzene in petrol.(640 words)

10.

State the name of the element which is oxidized in the reaction:

Zn(s) + Cu (aq) Zn (aq) + Cu(s) ........................................................................................................................................ ......(1)

2+

2+

11.

(a)

Name the type of intermolecular force between water molecules.

.............................................................................................................................. ......(1)

(b)

The HOH bond angle in water is .............................................................................................................................. ......(1) (Total 2 marks)

12.

(a) Pure samples of hydrogen halides, HC1, HBr and HI, are prepared by adding a suitable acid to the corresponding potassium halides. (i) Name the acid used. ................................................................................................................... .......(1)

(ii)

Draw a diagram of the apparatus you would use.

(2)

(b)

A testtube containing hydrogen chloride gas is inverted in water. Describe and explain what you would observe. Observation ......................................................................................................... ....... .............................................................................................................................. ......

Explanation ......................................................................................................... ....... .............................................................................................................................. ......(2)

(c)

(i) bromide?

What would you see when ammonia reacts with hydrogen

................................................................................................................... .......(1)

(ii)

What is the formula for the compound formed when ammonia reacts with hydrogen bromide? ................................................................................................................... .......(1)

(d)

A hot wire is plunged into testtubes containing each of the hydrogen halides. (i) Name the hydrogen halide which decomposes. ................................................................................................................... .......(1)

(ii)

Describe the appearance of the contents of the testtube as decomposition takes place. ................................................................................................................... .......(1)

(iii)

Write a balanced equation for the decomposition in (i).

1)

(e)

Water companies use chlorine to purify water for domestic use. Concentrations of chlorine are carefully monitored by testing water samples. 3 Excess potassium iodide was added to a 1000 cm sample of water. 3 The iodine formed reacted with 14.0 cm of 0.00100 m sodium thiosulphate solution. (i) Calculate the number of moles of sodium thiosulphate, Na2S2O3, used in the reaction.

(1)

(ii)

The ionic equation for the reaction between iodine and sodium thiosulphate is

I 2 (a q ) + 2 S 2O

2 3 (

aq)

2 I (aq ) + S 4 O

2 6 (

aq)

Calculate the number of moles of iodine molecules, I2, used in the reaction.

(1)

(iii)

Write the equation for the reaction between chlorine molecules, C12, and iodide ions.

(1)

(iv)

Write down the number of moles of chlorine in the sample. ................................................................................................................... .......(1)

(v)

Calculate the mass of chlorine molecules in the original sample.

(1)

(vi)

The maximum accepted concentration of chlorine in drinking water is 0.5 parts per million by mass. Show by calculation that the sample of water tested above is acceptable. You may assume 1000 cm of water has mass 1000 g.3

(1)

(vii) Suggest a reason why the concentration of chlorine in water must not exceed 0.5 ppm. ................................................................................................................... .......(1) (Total 17 marks)

13.

Pure samples of hydrogen halides, HC1, HBr and HI, are prepared by adding a suitable acid to the corresponding potassium halides. (i) Name the acid used. ................................................................................................................... .......(1)

(ii)

Draw a diagram of the apparatus you would use.

(2) (Total 3 marks)

14.

A testtube containing hydrogen chloride gas is inverted in water. Describe and explain what you would observe. Observation ......................................................................................................... ....... .............................................................................................................................. ...... Explanation ......................................................................................................... ....... .............................................................................................................................. ......(2)

15.

(i)

What would you see when ammonia reacts with hydrogen bromide? ................................................................................................................... .......(1)

(ii)

What is the formula for the compound formed when ammonia reacts with hydrogen bromide? ................................................................................................................... .......(1) (Total 2 marks)

16.

A hot wire is plunged into testtubes containing each of the hydrogen halides. (i) Name the hydrogen halide which decomposes. ................................................................................................................... .......(1)

(ii)

Describe the appearance of the contents of the testtube as decomposition takes place. ................................................................................................................... .......(1)

(iii)

Write a balanced equation for the decomposition in (i).

1) (Total 3 marks)

17.

Water companies use chlorine to purify water for domestic use. Concentrations of chlorine are carefully monitored by testing water samples. 3 Excess potassium iodide was added to a 1000 cm sample of water. 3 The iodine formed reacted with 14.0 cm of 0.00100 m sodium thiosulphate solution. (i) Calculate the number of moles of sodium thiosulphate, Na2S2O3, used in the reaction.

(1)

(ii)

The ionic equation for the reaction between iodine and sodium thiosulphate is

I 2 (a q ) + 2 S 2O

2 3 (

aq)

2 I (aq ) + S 4 O

2 6 (

aq)

Calculate the number of moles of iodine molecules, I2, used in the reaction.

(1)

(iii)

Write the equation for the reaction between chlorine molecules, C12, and iodide ions.

(1)

(iv)

Write down the number of moles of chlorine in the sample. ................................................................................................................... .......(1)

(v)

Calculate the mass of chlorine molecules in the original sample.

(1)

(vi)

The maximum accepted concentration of chlorine in drinking water is 0.5 parts per million by mass. Show by calculation that the sample of water tested above is acceptable. You may assume 1000 cm of water has mass 1000 g.3

(1)

(vii) Suggest a reason why the concentration of chlorine in water must not exceed 0.5 ppm. ................................................................................................................... .......(1) (Total 7 marks)

18.

Read the passage on pages 13 and 14 on ESCA a Practical Method for Determining Charges on Atoms in Molecules straight through, and then more carefully, in order to answer the following questions. (a) (i) In ammonia, NH3, the ionic character of the bond between nitrogen and hydrogen (NH) is 18%. State the charge on each hydrogen atom and hence calculate the charge on the nitrogen atom.(2)

(ii)

Explain why liquid ammonia is likely to be a good solvent for ionic compounds.(1)

(b)

Use the results given for the sulphate ion to calculate the charge on the sulphate ion.(1)

(c) (d)

Describe the shape of the thiosulphate ion with an appropriate diagram.(1)

(i)

Using the normal rules, calculate the oxidation number of2 S 2 O 3- .

sulphur in the thiosulphate ion, (ii)

(1)

Suggest a reason why oxidation numbers are not always the same as the true electric charge on atoms in molecules or ions consisting of several

atoms.(1)

(e)

Describe the process of electron spectroscopy for chemical analysis (ESCA) and explain how it can be used to give important information about atoms in molecules, in not more than 100 words. You are not asked to summarise the whole passage, nor to include equations in your summary. At the end of your summary state the number of words you have used.(8)

Credit will be given for answers written in good English, using complete sentences and with correct use of technical words. Avoid copying long sections from the original text. Numbers count as one word, as do standard abbreviations and hyphenated words. Any title you give to your passage does not count in your word total There are penalties for the use of words in excess of 100.(Total 15 marks)

ESCA a Practical Method for Determining Charges on Atoms in Molecules It is often useful to know actual charges on atoms in polar molecules. Such knowledge can help in the predictions of physical properties of compounds like the melting point, boiling point and solubility. It is also an aid to predicting and understanding chemical reactions. In molecules like HCI, H2O or NH3, determining the distribution of electric charge on the atoms is simple. The degree of ionic character of the bonds can be found by calculating the difference in electronegativity between the elements and then consulting an appropriate table of data. Consider the example of water, H2O. The difference in electronegativity gives 39% ionic character for the bond between oxygen and hydrogen. This means that the charge on each hydrogen atom is +0.39, and the charge on the oxygen atom is0.78.

0 .7 8 O + 0 .3 9 + 0 .3 9 H H This calculation shows that the oxygen atom in water has a very significant negative charge. This helps to explain the solubility of ionic compounds in water. Positive ions will be powerfully attracted to negative oxygen atoms in water molecules, and negative ions to the positive hydrogen atoms.The calculation of charge distribution becomes much more difficult when the molecules contain multiple or delocalized bonds, or the molecule is nonsymmetrical. It is more convenient to use experimental data instead of relying on theoretical calculations. The main source of experimental data about charge distribution in molecules is the permanent dipole moment, which is based on measurements of the effect of a substance on an applied electric field. Unfortunately the interpretation of such data is still difficult for complex molecules.

However, in the last twenty years the method of Xray spectroscopy has opened up new horizons in determining the distribution of charge in molecules and ions. There are three branches of spectroscopy which involve the interaction of Xrays with molecules: ESCA (electron spectroscopy for chemical analysis), Auger spectroscopy and Xray fluorescence spectroscopy.

When Xrays of known energy are absorbed by an atom an electron from an inner shell is expelled and the atom becomes a positive ion in a high energy state. ESCA is concerned with measuring the kinetic energy of the expelled electrons using an electron spectrometer. The kinetic energy of emitted electrons depends upon their binding energy within the atom. When electrons are held tightly the energy needed to release them is greater and the kinetic energy of electrons released is less. The kinetic energy of emitted electrons, Ek, is related to the energy of the Xrays, hvk, and the binding energy of the electrons, Eb, by the equation: Eb = hvk Ek The binding energy of an electron depends on the attractive force exerted by the positive nucleus on the negative electron. This is often referred to as the Coulombic force of attraction. The Coulombic attractive force is dependent on the effective charge on the nucleus; the higher the effective nuclear charge, the stronger the force of attraction. The effective charge on the nucleus is related to the partial charge on the atom. So the binding energy of an electron depends on the partial charge on an atom. A more detailed analysis shows that there is a linear relationship between electron binding energies and partial charges on atoms. Thus by measuring kinetic energies of electrons, it is possible through calculating electron binding energies to find partial charges on atoms relatively easily. The reason ESCA is so important is that it enables the charge on the individual atoms within molecules or ions to be calculated. Examples of ions where ESCA helps us to understand their electronic structure are the sulphate ion and the thiosulphate ion. In the sulphate ion ESCA shows that the ion consists of a sulphur atom with a charge of +1.12, and four oxygen atoms with equal charges of 0.78.

0 .7 8 O 0 .7 8 S + 1 .1 2 O O 0 .7 8

In the thiosulphate ion, 2 the oxygen atoms carry the same charge of 0.83, but one sulphur atom has a charge of 0.50, and the other has a charge of +0.99. These results are interesting and are quite different from the charges which would be assigned to sulphur and oxygen using the concept of oxidation number in these ions. They suggest that oxidation number, while useful as a concept, is not a good indicator of the true pattern of electric charge in an ion consisting of several atoms.

S O

23 ,

0 .7 8 O

(698 words)

Adapted from ESCA and molecular charge distribution, Jacques Furnemont, Education in Chemistry, Volume 31, Number 5, September 1994, The Royal Society of Chemistry.

19.

The table below gives the molar masses and boiling points of three carbon compounds.

M o la r m a s s /g m o l 1 B u ta n o n e , C 2 H 5 C O C H P e n ta n e , C 5 H12 12 3

B o ilin g P o in t / C 80 36 28

72 72 72

2 m e th y lb u ta n e , C 5 H(a)

What is the main type of interaction between molecules in (i) pure butanone? ........................................................................................ .(1 mark

(ii)

pure pentane? .......................................................................................... .(1 mark

(b)

Draw a diagram to illustrate the main interaction between two molecules of butanone.

(2)

(c)

Explain why pentane and 2methylbutane have different boiling points despite having the same molecular formula and molar mass. You may find drawing a diagram helpful.

(2)

(d)

When equal volumes of butanone and pentane are stirred together the liquids mix and there is a drop in temperature. When equal volumes of pentane and water are stirred together they separate into two layers when stirring is stopped. (i) Why is there a drop in temperature when butanone is mixed with pentane?

................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(2)

(ii)

Explain why pentane and water do not mix. ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(2) (Total 10 marks)

20.

(a) Boron, nitrogen and oxygen form fluorides with molecular formulae BF3, NF3 and OF2. Draw the shapes you would expect for these molecules, suggesting a value for the bond angle in each case. BF3

FBF bond angle = NF3

FNF bond angle = OF2

FOF bond angle =(3)

(b)

(i) Calculate the standard enthalpy change of atomization of nitrogen trifluoride, H e[NF3(g)]. Your answer should include a sign and units.

Use the Hess cycle, and the data at 298 K: H f [NF3(g)] H e [N2(g)] H e [F2(g)] N H

= = = H a t ( g )

124.7 kJ mol

1

+472.7 kJ mol

1

3

F F1 2

[3 N ) ] ( 32g 2 )

+79.0 kJ mol F ( g ) ] N ( g ) + 3

1

F

( g

)

f

[ 3N

( g N2

+

F

( g

)

(3)

(ii) (c)

Use your answer to (i) to calculate the bond energy of the NF bond(1)

Another fluoride of nitrogen has the formula N2F2. (i) Draw a dotandcross diagram for the electronic structure of N2F2 showing outer shell electrons only.

(2)

(ii)

Draw diagrams to show two possible shapes for the N2F2 molecule

(1)

(iii)

The NF bond energy in N2F2 is 282.0 kJ mol . Suggest a reason for the differences between this value and the value you calculated for the NF bond in NF3 in (b)(ii).

1

................................................................................................................... ....... ................................................................................................................... .......(1)

(d)

BF3 and NF3 react together readily to give a solid with composition BN3NF3. (i) Draw a dotand cross diagram for the electronic structure of BF3NF3 showing outer shell electrons only.

(1)

(ii)

What is the type of bond between the nitrogen and boron atoms? ................................................................................................................... .......(1)

(e)

Suggest a balanced equation for the reaction of 1 mole of OF2 with 1 mole of water to form two products.

(2) (Total 15 marks)

21.

(a)3

This part of the question is about the hydrolysis of halogenoalkanes.

2 cm of ethanol is added to each of three test-tubes. Three drops of 1chlorobutane are added to the first, three drops of 1 bromobutane to the second, and three drops of 1iodobutane to the third testtube. 2cm portions of hot aqueous silver nitrate solution are added to each testtube. A precipitate forms immediately in the third test-tube, slowly in the second test-tube and extremely slowly in the first test-tube. In each reaction the precipitate is formed by silver ions. Ag (aq), reacting with the halide ions formed by hydrolysis of the halogenoalkane. (i) Why was ethanol added to each test-tube? ................................................................................................................... .......+ 3

(1)

(ii)

The same organic product forms in each reaction. Name this organic product. ................................................................................................................... .......(1)

(iii)

Complete the equation for the hydrolysis of 1bromobutane C4 H9 Br + H2O (2)

(iv)

What is the colour of the precipitate in the third test-tube? ................................................................................................................... .......(1)

(v)

Name the precipitate which forms extremely slowly in the first testtube and write the ionic equation, including state symbols, for its formation. Name of precipitate........................................................................................ .... Ionic equation........................................................................................... .........(3)

(vi)

Ammonia solution is added to the precipitate formed in the first testtube. Describe and explain what you would observe. Description................................................................................................. ....... ................................................................................................................... ....... Explanation................................................................................................ ........ ................................................................................................................... .......(2)

(vii) Explain why the rates of hydrolysis of the three halogenoalkanes are different ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......

................................................................................................................... .......(2)

(b)

1bromobutane reacts with an alcoholic solution of potassium hydroxide at high temperature to form but1ene. (i) Draw a fully labelled diagram to show an apparatus for carrying out this reaction in the laboratory and collecting the gaseous but1ene

(3)

(ii)

Suggest a chemical test for an alkene such as but1ene. State the colour change you would observe. Reagent...................................................................................................... ....... Colour change from.................................................to.......................................(2) (Total 17 marks)

22.

(a)

, react with iodide ions in aqueous solution to 2 form iodine and sulphate ions. S O 4 . (i) What is the oxidation number of iodine in iodine molecules, I2............................................................................................ iodide ions, I ....................................................................................................(1)

Persulphate ions, S O

2 8

(ii)

The oxidation number of sulphur is +6 in both sulphate and persulphate ions. What is the oxidation number of oxygen in sulphate ion, 2 SO4 ............................................................................................. persulphate ion, 2 S2O8 ......................................................................................(1)

(iii)

Identify the oxidant (oxidizing agent) in the reaction. ................................................................................................................... .......(1)

(iv)

Write a balanced equation for the reaction between persulphate ions and iodide ions.

(1)

(b)

The effect of persulphate ion concentration on the rate of this reaction can be measured as follows. Some starch solution and a small measured quantity of sodium thiosulphate solution are added to potassium persulphate solution. Potassium iodide solution is added and the time measured for the solution to change colour. This occurs when all the sodium thiosulphate is used up and the starch reacts with the iodine. The reaction is repeated using difference concentrations of potassium persulphate.

(i)

What is the final colour of the reaction mixture? ................................................................................................................... .......(1)

(ii)

Why is the concentration of iodide ions constant until the reaction mixture changes colour? ................................................................................................................... ....... ................................................................................................................... .......(1)

(c)

The rate of reaction is measured by taking the reciprocal of the time for the colour of the reaction mixture to change. Typical results are shown in the table below. [S 2 O 8 (a q )] /m o l d m 3 0 .0 1 0 0 0 .0 0 9 0 0 .0 0 7 5 0 .0 0 6 02

tim e /s 480 533 640 800

1 /tim e /s 1 2 .0 8 1 0 1 .8 8 1 0 1 .5 6 1 0 1 .2 5 1 03 3 3 3

(i)

Plot a graph of 1/time on the vertical axis against concentration of persulphate ions on the horizontal axis.

(3)

(ii)

Use your graph to deduce the order of the reaction with respect to persulphate ions. Justify your answer. ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(2)

(d)

(i) The reaction is first order with respect to iodide ions. Use this information and your answer to (c)(ii) to write the overall rate equation for the reaction.

................................................................................................................... .......(1)

(ii)

What are the units of the rate constant for the reaction? ................................................................................................................... .......(1) (Total 13 marks)

23.

Read the passage on BENZENE straight through, and then more carefully, in order to answer the following questions. (a) (ii) (i) Draw the displayed formula for benzene(1)

Write a balanced equation for the dehydrogenation of cyclohexane, C6H12, to benzene, C6H6.(1)

(iii)

Suggest ONE reason why platforming might be preferred to using aluminium oxide(1)

(b)

Classify the following reactions as substitution, elimination or addition reactions. (i) The reaction between benzene and chlorine to form 1,2,3,4,5,6hexachlorocyclohexane(1)

(ii) (c)

The reaction between benzene and chlorethene to form ethylbenzene(1)

Name the chemical used to produce dodecylbenzenesulphonic acid from dodecylbenzene.(1)

(d)

Write a summary in continuous prose, in no more than 100 words, describing the production of benzene from petroleum. You are NOT asked to summarise the whole passage, nor to include equations in your summary. At the end of your summary state the number of words you have used.(9)

Credit will be given for answers written in good English, using complete sentences and with correct use of technical words. Avoid copying long sections from the original text. Numbers count as one word, as do standard abbreviations and hyphenated words. Any title you give to your passage does not count in your word total. There are penalties for use of words in excess of 100.(Total 15 marks)

BENZENE Benzene was first discovered by Michael Faraday in London in 1825. By this time gas lighting was becoming common in London. The Portable Gas Company was producing gas by heating whale oil in a furnace. When they compressed the gas to

put it in cylinders an oily liquid separated out. They told Faraday about this and he set about identifying the liquid. He distilled it and collected a fraction which boiled at 80C and condensed to a clear liquid. We now know this as benzene. In 1834 Mitscherlich discovered that the same colourless liquid could be obtained by heating benzoic acid with lime. In 1845 Hofmann demonstrated the presence of benzene in coal naphtha, the lowest boiling fraction obtained by the distillation of coal tar, and in 1848 Mansfield succeeded in isolating benzene from coal naphtha. Now most benzene is produced from petroleum. Petroleum is fractionally distilled to separate the crude oil into fractions on the basis of their boiling points. A typical crude oil composition is 2% butane, 11% petrol, 14% naphtha, 17% furnace oil, 39% gas oil and 17% residue. The naphtha fraction which contains hexane is used to produce benzene. The naphtha fraction is purified to remove sulphur compounds which would poison the catalyst used in the process. Sulphur compounds are removed by reduction to form hydrogen sulphide. This is known as hydrodesulphurisation (HDS) and leaves a very low concentration of sulphur in naphtha. The hydrogen sulphide produced is used to manufacture sulphur and sulphuric acid. This treatment was originally only used in the production of sulphurfree fuels but it is now used to reduce the sulphur content of most crude oil fractions. Purified naphtha is now heated to about 770 K. It then passes into a reactor where one of two processes may be used, depending on the catalyst. An aluminium oxide catalyst may be used with the reactants at a pressure of 40 atmospheres. Hexane first reacts to form cyclohexane and hydrogen. Then cyclohexane is dehydrogenated to form benzene. Other aromatics like methylbenzene and dimethylbenzenes are also produced. The mixture of products is dissolved in a suitable solvent. The aromatic products are separated from the solvent by further distillation in fractionating towers. Residual impurities are removed, for example, by passing through an active clay catalyst. A final fractionation is then used to separate and purify benzene. The second process is called platforming because it uses the metal platinum. In platforming the same chemical reactions are involved. The difference is that a platinum catalyst is used, in spite of the extra expense, and a lower pressure of 15 atmospheres is sufficient. Benzene is the starting material for a large number of useful chemicals and materials. The insecticide BHC, benzenehexachloride (systematic name, 1,2,3,4,5,6 hexachlorocyclohexane) is made by passing chlorine through benzene irradiated by ultraviolet light. BHC is particularly valuable in the fight against the locust. Benzene is the starting material for the manufacture of many plastics. By reacting benzene with chloroethane in the presence of an aluminium chloride

catalyst at 80C, ethylbenzene is formed. This is dehydrogenated by heating to 600 C with a zinc oxide catalyst to produce phenylethene (styrene) which polymerizes to form polystyrene. Benzene is also the starting material for making many soapless detergents. Benzene reacts with dodeclene in the presence of a suitable catalyst to produce dodecylbenzene. ( C +2C 2 2 H 1 1 3

)

C

H

1

4

H

The dodecylbenzene is then sulphonated to produce dodecylbenzenesulphonic acid which can then be neutralized to produce sodium dodecylbenzenesulphonate, a biodegradable soapless detergent. So it can be seen that from Faraday's discovery a vast and vital range of chemicals has developed. (590 words)

24.

The gases hydrogen sulphide, H2S, and sulphur dioxide, SO2, react according to the equation 2H2S(g) + SO2(g) 3S(s) + 2H2O(1) (a) Explain why water is a liquid but hydrogen sulphide is a gas at room temperature, even though a hydrogen sulphide molecule has almost twice the mass of a water molecule. .............................................................................................................................. ...... .............................................................................................................................. ...... .............................................................................................................................. ...... .............................................................................................................................. ...... .............................................................................................................................. ...... .............................................................................................................................. ......(2)

(b)

Which of the four substances in the equation would you expect to have the lowest entropy at 298 K? Justify your answer. .............................................................................................................................. ...... .............................................................................................................................. ...... ..............................................................................................................................

...... .............................................................................................................................. ......(2)

(c)

(i) Would you expect Ss positive or negative value? Justify your answer.

y

s for m the t e

reaction to have a

................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(2)

(ii)

The reaction is know to be spontaneous at 298 K. u What can you deduce about Ss u r r o ? n d i n g

s

................................................................................................................... ....... ................................................................................................................... .......(2)

(iii)

What can you deduce about H ? ................................................................................................................... ....... ................................................................................................................... .......(1) (Total 9 marks)

t

25.

Iodine is only slightly soluble in water, but it is much more soluble in organic solvents and also in aqueous potassium iodide solution. (a) What is the colour of iodine (i) solid .......................................................................................................... ..... (ii) (iii) dissolved in hydrocarbon solvent ................................................................... dissolved in potassium iodide solution? .........................................................(3)

(b)

A solution of iodine in a hydrocarbon solvent was shaken with water until 3 equilibrium was reached. The mixture was allowed to settle and then 5 cm of 3 the hydrocarbon solvent layer and 50 cm of the aqueous layer were removed and titrated separately with sodium thiosulphate solution of concentration 3 0.0100 mol dm . The following results were obtained.

S

o

l v e nV t o l u m s o l u t i o / c 3m d r o c a r 5b 5 0 o n

e n

Vo of l u m e o f u s so e d d i u m t h s o l u t i o n / c m3 7 8 6 . 9

0 3 . 0 I 12 0 c 0 o nm c o e l n dt r m a i o s u l / p m h oa lt 3 e d m u s e d ? 8 . 9 4

t i

H

y W

a t e r

1

0

(i)

Which indicator, if any, would you use for this titration and what would the colour change be at the end point? Indicator .................................................................................................... ....... Colour change from ............................................... to .......... ....................(3)

(ii)

The equation for the reaction between iodine and sodium thiosulphate is I2(aq) + 2Na2S2O3(aq) 2NaI(aq) + Na2S4O6(aq) Calculate the concentration of iodine molecules, I2, in mol dm in the hydrocarbon layer.3

(2)

(iii)

Use your knowledge of intermolecular forces to explain why iodine dissolves so much more in a hydrocarbon than in water. ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(2)

(iv)

When a solution of iodine in a hydrocarbon solvent is shaken with water the following equilibrium occurs. I2(hydrocarbon)

I2

(water)

Write down an expression for Kc for this equilibrium and calculate its value. Kc =

(2)

(v)

Suggest two improvements to this titration procedure which would increase its accuracy. Assume that the results table is a complete record of all of the practical work carried out. ................................................................................................................... ....... ...................................................................................................................

....... ................................................................................................................... ....... ................................................................................................................... .......(2)

(vi)

How would you expect the value of Kc to change when the concentration of iodine molecules, I2, in the hydrocarbon solvent at the start is doubled? ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(1)

(c)

The experiment was repeated using potassium iodide solution instead of water. The following equilibrium was set up in the aqueous layer: I2(aq) + I (aq)I3

(aq)

How would you expect this to affect the volume of sodium thiosulphate solution used in the titration of the aqueous layer? Justify your answer. ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(2) (Total 17 marks)

26.

A solution of iodine in a hydrocarbon solvent was shaken with water until

equilibrium was reached. The mixture was allowed to settle and then 5 cm of the 3 hydrocarbon solvent layer and 50 cm of the aqueous layer were removed and titrated separately with sodium thiosulphate solution of concentration 0.0100 mol 3 dm . (a) The following results were obtained. S o l v e nV t o l u m s o l u t i o / c 3m d r o c a r 5b 5 0 o n e n Vo of l u m e o f u s so e d d i u m t h s o l u t i o n / c m3 7 8 6 . 9 8

3

0 3 . 0 I 12 0 c 0 o nm c o e l n dt r m a i o s u l / p m h oa lt 3 e d m u s e d ? . 9 4

t i

H

y W

a t e r

1

0

(i)

Which indicator, if any, would you use for this titration and what would the colour change be at the end point? Indicator .................................................................................................... ....... Colour change from ............................................... to .......... ....................(3)

(ii)

The equation for the reaction between iodine and sodium thiosulphate is I2(aq) + 2Na2S2O3(aq) 2NaI(aq) + Na2S4O6(aq) Calculate the concentration of iodine molecules, I2, in mol dm in the hydrocarbon layer.3

(2)

(iii)

Use your knowledge of intermolecular forces to explain why iodine dissolves so much more in a hydrocarbon than in water. ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(2)

(iv)

When a solution of iodine in a hydrocarbon solvent is shaken with water the following equilibrium occurs. I2(hydrocarbon)

I2

(water)

Write down an expression for Kc for this equilibrium and calculate its value. Kc =

(2)

(v)

Suggest two improvements to this titration procedure which would increase its accuracy. Assume that the results table is a complete record of all of the practical work carried out. ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(2)

(vi)

How would you expect the value of Kc to change when the concentration of iodine molecules, I2, in the hydrocarbon solvent at the start is doubled? ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(1)

(b)

The experiment was repeated using potassium iodide solution instead of water. The following equilibrium was set up in the aqueous layer: I2(aq) + I (aq)I 3 (aq)

How would you expect this to affect the volume of sodium thiosulphate solution used in the titration of the aqueous layer? Justify your answer. ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......

................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(2) (Total 14 marks)

27.

Trichloromethane, CHCl3, has dipoledipole interactions between its molecules, as has ethoxyethane, CH3CH2OCH2CH3. Hexane, C6H14, has only van der Waals interactions.

(a)

In an experiment to measure the strength of the dipoledipole interactions in trichloromethane, 10g of trichloromethane was mixed with 30g of hexane. The dipoledipole interactions were disrupted and the temperature fell by 1.1 C. S u b s ta n c e E th o x y e th a n e H exane T r ic h lo r o m e th a n e M a s s o f 1 m o le /g 7 4 .1 8 6 .2 1 1 9 .4 S p e c ific h e a t c a p a c ity /J g 1 K 1 2 .2 8 2 .2 6 0 .9 8 D e n s ity /g c m 3 0 .7 1 0 .6 6 1 .4 8 B o ilin g p o in t /C 35 69 62

Use this information to calculate a value for the strength of the dipoledipole interactions in 1 mole of trichloromethane.(3)

(b)

When trichloromethane is mixed with ethoxyethane a hydrogen bond is formed between the molecules. Plan how you would carry out an experiment to measure the strength of this hydrogen bond. In your account you should include: a displayed formula to show the hydrogen bond between the two molecules; a justification of the quantities of each substance you would use; details of the apparatus you would choose to ensure an accuracy of at least 5%; any risks involved and hence safety precautions you would take; details of how you would calculate the strength of the hydrogen bond from your results and the approximate value you would expect.(9)

(c)

Comment on the likely solubility of these three organic substances in water.(3) (Total 15 marks)

28.

Trichloromethane, CHCl3, has dipoledipole interactions between its molecules, as has ethoxyethane, CH3CH2OCH2CH3. Hexane, C6H14, has only van der Waals interactions.

In an experiment to measure the strength of the dipoledipole interactions in trichloromethane, 10g of trichloromethane was mixed with 30g of hexane. The dipoledipole interactions were disrupted and the temperature fell by 1.1 C. S u b s ta n c e E th o x y e th a n e H exane T r ic h lo r o m e th a n e M a s s o f 1 m o le /g 7 4 .1 8 6 .2 1 1 9 .4 S p e c ific h e a t c a p a c ity /J g 1 K 1 2 .2 8 2 .2 6 0 .9 8 D e n s ity /g c m 3 0 .7 1 0 .6 6 1 .4 8 B o ilin g p o in t /C 35 69 62

Use this information to calculate a value for the strength of the dipoledipole interactions in 1 mole of trichloromethane.(3)

29.

When trichloromethane is mixed with ethoxyethane a hydrogen bond is formed between the molecules. Plan how you would carry out an experiment to measure the strength of this hydrogen bond. (a) In your account you should include: a displayed formula to show the hydrogen bond between the two molecules; a justification of the quantities of each substance you would use; details of the apparatus you would choose to ensure an accuracy of at least 5%; any risks involved and hence safety precautions you would take; details of how you would calculate the strength of the hydrogen bond from your results and the approximate value you would expect.(9)

(b)

Comment on the likely solubility of these three organic substances in water.(3) (Total 12 marks)

30.

The boiling points and molar masses of the hydrogen halides are given in the table.

H y d ro g e n h a lid e h y d ro g e n flu o r id e h y d ro g e n c h lo r id e h y d ro g e n b ro m id e h y d ro g e n io d id e (a)

M o la r m a s s /g m o l 1 2 0 .0 3 6 .5 8 0 .9 1 2 7 .9

B o ilin g p o in t /K 293 188 206 238

Why do the boiling points increase from hydrogen chloride to hydrogen iodide as molar mass increases? .............................................................................................................................. ...... .............................................................................................................................. ......(1)

(b)

(i) Name the strong attractive force between hydrogen fluoride molecules which accounts for the unusually high boiling point. ................................................................................................................... .......(1)

(ii)

Draw a diagram showing the attractive force between two hydrogen fluoride molecules.

(1) (Total 3 marks)

31.

(a) Boron, nitrogen and oxygen form fluorides with molecular formulae BF3, NF3 and OF2. Draw the shapes you would expect for these molecules, suggesting a value for the bond angle in each case. BF3

FBF bond angle =

NF3

FNF bond angle = OF2

FOF bond angle =(3)

(b)

(i) Calculate the standard enthalpy change of atomization of nitrogen trifluoride, H e [NF3(g)]. Your answer should include a sign and units. Use the Hess cycle, and the data at 298 K: H f [NF3(g)] = 124.7 kJ mol1

H e[N2(g)] = H e[F2(g)] N H

+472.7 kJ mol +79.0 kJ mol [3 N ) ] ( 32g 2 ) F N

1

=

1

3

F F1 2

H a t ( g ) ( g N2

( g ( g

) ] ) +

3

F

( g

)

f

[ 3N

+

F

( g

)(3)

(ii) (c)

Use your answer to (i) to calculate the bond energy of the NF bond.(1)

Another fluoride of nitrogen has the formula N2F2. (i) Draw a dotandcross diagram for the electronic structure of N2F2 showing outer shell electrons only.

(2)

(ii)

Draw diagrams to show two possible shapes for the N2F2 molecule.

(1)

(iii)

The NF bond energy in N2F2 is 282.0 kJ mol . Suggest a reason for the difference between this value and the value you calculated for the NF bond in NF3 in (b)(ii). ...................................................................................................................

1

....... ................................................................................................................... .......(1)

(d)

BF3 and NF3 react together readily to give a solid with composition BN3NF3. (i) Draw a dot-and cross diagram for the electronic structure of BF3NF3 showing outer shell electrons only.

(1)

(ii)

What is the type of bond between the nitrogen and boron atoms? ................................................................................................................... .......(1)

(e)

Suggest a balanced equation for the reaction of 1 mole of OF2 with 1 mole of water to form two products.

(2) (Total 15 marks)

32.

(a)3

This part of the question is about the hydrolysis of halogenoalkanes.

2 cm of ethanol is added to each of three test-tubes. Three drops of 1chlorobutane are added to the first, three drops of 1 bromobutane to the second, and three drops of 1iodobutane to the third testtube. 2cm portions of hot aqueous silver nitrate solution are added to each testtube. A precipitate forms immediately in the third test-tube, slowly in the second test-tube and extremely slowly in the first test-tube. In each reaction the precipitate is formed by silver ions, Ag (aq), reacting with the halide ions formed by hydrolysis of the halogenoalkane. (i) Why was ethanol added to each test-tube? ................................................................................................................... .......+ 3

(1)

(ii)

The same organic product forms in each reaction. Name this organic product. ................................................................................................................... .......(1)

(iii)

Complete the equation for the hydrolysis of 1bromobutane. C4H9Br + H2O (2)

(iv)

What is the colour of the precipitate in the third test-tube? ................................................................................................................... .......(1)

(v)

Name the precipitate which forms extremely slowly in the first testtube and write the ionic equation, including state symbols, for its formation. Name of precipitate ....................................................................................... .... Ionic equation .......................................................................................... ..........(3)

(vi)

Ammonia solution is added to the precipitate formed in the first testtube. Describe and explain what you would observe. Description ................................................................................................ ...... ................................................................................................................... ....... Explanation .................. ................................................................................ ................................................................................................................... .......(2)

(vii) Explain why the rates of hydrolysis of the three halogenoalkanes are different. ................................................................................................................... ....... ................................................................................................................... ....... ...................................................................................................................

....... ................................................................................................................... .......(2)

(b)

1bromobutane reacts with an alcoholic solution of potassium hydroxide at high temperature to form but1ene. (i) Draw a fully labelled diagram to show an apparatus for carrying out this reaction in the laboratory and collecting the gaseous but1ene.

(3)

(ii)

Suggest a chemical test for an alkene such as but1ene. State the colour change you would observe. Reagent ..................................................................................................... ....... Colour change from ......................................... to .......................................(2) (Total 17 marks)

33.

(a)

Persulphate ions,

2 S2 O8 -

, react with iodide ions in aqueous solution to

2form iodine and sulphate ions SO 4 .

(i)

What is the oxidation number of iodine in iodine molecules, I2 .......................................................................................... iodide ions, I ........................................................................(1)

(ii)

The oxidation number of sulphur is +6 in both sulphate and persulphate ions. What is the oxidation number of oxygen in sulphate ion, SO 4 .............................................................................................2-

S O 2persulphate ion, 2 8 ...................................................................

(1)

(iii)

Identify the oxidant (oxidizing agent) in the reaction. ................................................................................................................... .......(1)

(iv)

Write a balanced equation for the reaction between persulphate ions and iodide ions.

(1)

(b)

The effect of persulphate ion concentration on the rate of this reaction can be measured as follows. Some starch solution and a small measured quantity of sodium thiosulphate solution are added to potassium persulphate solution. Potassium iodide solution is added and the time measured for the solution to change colour. This occurs when all the sodium thiosulphate is used up and the starch reacts with the iodine. The reaction is repeated using different concentrations of potassium persulphate. (i) What is the final colour of the reaction mixture? ................................................................................................................... .......(1)

(ii)

Why is the concentration of iodide ions constant until the reaction mixture changes colour? ................................................................................................................... ....... ................................................................................................................... .......(1)

(c)

The rate of reaction is measured by taking the reciprocal of the time for the colour of the reaction mixture to change. Typical results are shown in the table below. [S 2 O 8 (a q )] /m o l d m 3 0 .0 1 0 0 0 .0 0 9 0 0 .0 0 7 5 0 .0 0 6 02

tim e /s 480 533 640 800

1 /tim e /s 1 2 .0 8 1 0 1 .8 8 1 0 1 .5 6 1 0 1 .2 5 1 03 3 3 3

(i)

Plot a graph of 1/time on the vertical axis against concentration of persulphate ions on the horizontal axis.

(3)

(ii)

Use your graph to deduce the order of the reaction with respect to persulphate ions. Justify your answer. ................................................................................................................... ....... ................................................................................................................... ....... ................................................................................................................... .......(2)

(d)

(i) The reaction is first order with respect to iodide ions. Use this information and your answer to (c)(ii) tow rite the overall rate equation for the reaction.

................................................................................................................... .......(1)

(ii)

What are the units of the rate constant for the reaction? ................................................................................................................... .......(1) (Total 13 marks)

34.

Ionization energies in Kj mol of three elements R, S and T which are consecutive in atomic number are:

1

1st R S T(a)

2nd 2297 2666 3051

3 rd 3822 3931 4412

4 th 5158 5771 5877

5 th 6542 7238 7975

6 th 9362 8781 9649

7 th 11 018 11 996 11 343

1251 1521 419

In which Group of Periodic Table would T be found? Justify your answer. .............................................................................................................................. ...... .............................................................................................................................. ...... .............................................................................................................................. ...... .............................................................................................................................. ......(2)

(b)

Estimate the 8 ionization energy of the element S to 2 significant figures. .............................................................................................................................. ......(2)

th

(c)

What type of electron (s, p, etc) is removed when an atom of R is ionized by the removal of 1 electron? .............................................................................................................................. ......(1)

(d)

Write an equation with state symbols to represent the reaction accompanied by the second ionization energy of T (use T as the symbol for the element). .............................................................................................................................. ......(2)

(e)

The sketch graph shows the first ionization energies of R, S and T. Continue the sketch so as to show the pattern of the first ionization energies of the next three elements of the Periodic Table, U, V and W, assuming that transition elements are not involved. 1500

1000 io n iz a tio n e n e rg y 500

R (f)

S

T

U

V

W(3)

The first six ionization energies of another element M are

io n iz a tio n e n e rg y

1

2 3 4 e le c tr o n s re m o v e d

5

6

Explain why M cannot have an atomic number less than 12. .............................................................................................................................. ...... .............................................................................................................................. ......

.............................................................................................................................. ...... .............................................................................................................................. ......(3) (Total 13 marks)

35.

(a) Propane, C3H8, is used as a feedstock for making ethene using a cracking process. The yield of ethene is about 42%. (i) Write an equation for the cracking of propane to form ethene using displayed formulae.

(2)

(ii)

Draw a labelled diagram of an ethene molecule, showing the electron density distribution in the and bonds between the carbon atoms.

(2)

(b)

The cracking of propane also produces propene.C 3 H 8 (g ) C 3H 6 (g ) + H 2 (g )

Calculate the standard enthalpy change for this reaction. Use the data, at 298 K. H f [C3H8(g)] = 104.5 kJ mol H f [C3H6(g)] = +20.2 kJ mol Your answer should include a sign and units.1

1

(2)

(c)

Propene can be used to make a number of important chemical products. The processes involved can be summarized in the diagram: H C o m Ap o u n d C P e C R d2H 3H

O r o p C C H

3 a n

C

2

C o l

H

B i n

r t h2

a r k

B a n C H 3 e n e R

d

P

r o 2

p

H 1

e a c t i o n

e a c t i o n

C (i)

2H

C 2

H

P

o C l Hy

( p r o

p C e ln

e )

Give the displayed formula and name of compound A.

Name.......................................................................................................... .......(2)

(ii)

State the type of reaction occurring and the type of reagent used in the formation of compound A. Type of reaction ........................................................................................... ...... Type of reagent ............................................................................................ ......(2)

(iii)

Give the formulae of compounds B and C. B ................................................................................................................ ....... C ...............................................................................................................

........(2)

(iv)

Write a balanced equation for the formation of poly(propene) for propene in Reaction 1.

(2)

(v)

Suggest a reagent and condition for Reaction 2. Reagent ..................................................................................................... ........ Condition .................................................................................................. ........(2)

(vi)

State the type of mechanism in the substitution in Reaction 2. ................................................................................................................... .......(1)

(vii) Give the systematic name for CH2==CHCH2 C1. ................................................................................................................... .......(1) (Total 18 marks)