Physical Sciences P2 Learner Guide July 2011

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Physical Sciences P2 Exam Revision Learners Guide Winter School July 2011

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Introduction:

Have you heard about Mindset? Mindset Network, a South African non-profitorganisation, was founded in 2002. We develop and distribute quality andcontextually relevant educational resources for use in the schooling, health andvocational sectors. We distribute our materials through various technology platformslike TV broadcasts, the Internet (www.mindset.co.za/learn ) and on DVDs. Thematerials are made available in video, print and in computer-based multimediaformats.

At Mindset we are committed to innovation. In the last two years, we successfully rana series of broadcast events leading up to and in support of the NSC examinations

Now we are proud to announce our 2011 edition of Matric Exam Revision, which willbegin with our Winter School in July. Weve expanded the broadcast to support youin seven subjects - Mathematics, Physical Sciences, Life Sciences, MathematicalLiteracy, English 1 st Additional Language, Accounting and Geography.

During our Winter School, you will get Exam overviews, study tips on each of thetopics we cover, detailed solutions to selected questions from previous examinationpapers, short question and answer sessions so you can check you are on track andlive phone in programmes so you can work through more exam questions with anexperienced teacher.

Getting the most from Winter SchoolBefore you watch the broadcast of a topic, read through the questions for the topic

and try to answer them without looking up the solutions. If you get stuck and cantcomplete the answer dont panic. Make a note of any questions you have. Whenwatching the Topic session, compare the approach you took to what the teacherdoes. Dont just copy the answers down but take note of the method used.

Make sure you keep this booklet for after Winter School. You can re-do the examquestions you did not get totally correct and mark your own work by looking up thesolutions at the back of the booklet.

Remember that exam preparation also requires motivation and discipline, so try tostay positive, even when the work appears to be difficult. Every little bit of studying,

revision and exam practice will pay off. You may benefit from working with a friend ora small study group, as long as everyone is as committed as you are. Mindsetbelieves that the 2011 Winter School programme will help you achieve the resultsyou want.

If you find Winter School a useful way to revise and prepare for your exams,remember that we will be running Spring School from the 3 rd to 7 th October andExam School from 19 th October to 22 nd November as well.
http://www.mindset.co.za/learnhttp://www.mindset.co.za/learnhttp://www.mindset.co.za/learnhttp://www.mindset.co.za/learn


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Topic 1: Organic Chemistry

Question 1The table below shows the results obtained during a practical investigation. Twoexperiments were performed to determine the boiling points of compounds fromthree different homologous series under the same conditions. Each letter A to Frepresents the organic compound written in the block next to it.

Experiment Organic compound Molar mass(gmol -1)Boiling point

(C)

IA CH3COOH 60,5 118B CH3CH2CH 2OH 60,1 97C CH3CH2CHO 58,1 48

IID CH3(CH 2)2COOH 88,1 163E CH3(CH 2)3CH2OH 88,1 137F CH3(CH 2)3CHO 88,1 103

1.1 Name the homologous series to which each of the following pairs ofcompounds belong:1.1.1 A and D (1)

1.1.2 B and E (1)

1.1.3 C and F (1)

1.2 Write down the IUPAC name for:1.2.1 Compound C (1)

1.2.2 Compound E (1)

1.3 Formulate an investigative question for this practical investigation. (2)

1.4 Which other variable, apart from the conditions for determining boiling points,was kept constant? (1)

1.5 What conclusion can be drawn from the results in Experiment II? (2)

1.6 Refer to intermolecular forces to explain the trend in boiling points, as shownin the table. (3)

Question 2The flow diagram below shows the conversion of propene to a secondary alcohol.

2.1 Give a reason why propene is classified as an unsaturated organiccompound. (1)

SubstitutionH2O

HBrPropene Compound X Secondary alcohol


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2.2 Use structural formulae to write a balanced equation for the formation ofcompound X. (4)

2.3 Name the type of reaction that takes place when propene is converted tocompound X. (1)

2.4 Write down the structural formula and IUPAC name for the secondary alcoholthat is formed (3)

2.5 Name the type of substitution reaction that takes place when compound X isconverted to the secondary alcohol. (1)

2.6 With the aid of a catalyst, propene can be converted directly to the secondaryalcohol, without the formation of the intermediate compound X.

2.6.1 Besides propene, write down the NAME of the reactant needed for thisdirect conversion. (1)

2.6.2 Write down the FORMULA of a catalyst that can be used. (1)

2.6.3 Name the type of reaction that will take place during this directconversion. (1)

2.7 Instead of adding water to compound X, concentrated sodium hydroxide isadded and the mixture is heated.

2.7.1Write down the IUPAC name of the organic product that is formed. (1)

2.7.2 Name the type of reaction that takes place. (1)

Question 3There are two structural isomers for the organic compound with molecular formulaC2H4O2.

3.1 Define the term structural isomer . (2)

3.2 Write down the structural formula of these two isomers and next to each its

IUPAC name. (6)

3.3 State with reasons which ONE of these isomers:

3.3.1 Has the higher boiling point (3)

3.3.2 Has the higher vapour pressure (3)

3.4 Will the vapour pressure of carboxylic acids increase or decrease if thenumber of carbon atoms in the chain increases? Give a reason for youranswer. (3)


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Question 4Many of the flavours and odours of fruits are esters. Ethyl ethanoate is the mostcommon ester found in wines and contributes to the perception of the fruitiness ofwine. A learner wants to prepare ethyl ethanoate in the school laboratory. Shefollows the instructions below.

Mix 1 cm 3 ethanoic acid and 1 cm 3 ethanol thoroughly in a test tube.Slowly add 4 drops of concentrated sulphuric acid while swirling the test tube.Soak a paper towel in cold water and fasten it around the test tube close to itsmouth with an elastic band.Place the test tube in a water bath and heat the water with a flame to atemperature of about 60 C.Leave the test tube in the hot water bath for about 15 minutes.Cool the test tube by placing it in a beaker of cold water.Smell the vapour in the test tube after 10 minutes.

Apparatus

4.1 To which homologous series does ethanol belong? (1)

4.2 Use structural formulae to write a balanced equation for the reaction takingplace in the test tube (5)

4.3 What is the function of the sulphuric acid in the above reaction? (1)

4.4 Why does the method use a water bath instead of direct heating over an openflame? (1)

4.5 State ONE function of the wet paper towel at the top of the test tube. (1)

4.6 The learner finds it difficult to detect the smell of the ester due to the presenceof sulphuric acid and unreacted ethanoic acid. A friend suggests that sheadd 10 drops of a diluted sodium carbonate solution to the contents of the testtube. Briefly explain why this suggestion might be a solution to the problem.

(2)

4.7 Whilst several esters may be present in wine, the observed aroma is generallythat of the smallest ester present in wine, namely ethyl ethanoate. State aphysical property of ethyl ethanoate which is responsible for this. (1)

Ethanol + ethanoic acid + 4 drops of sulphuric acid

Water bathPaper towel soaked in cold water

Thermometer


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Topic 2: Rates & Chemical Equilibrium

Question 1A group of learners use the reaction between hydrochloric acid and magnesiumpowder to investigate one of the factors that influence the rate of a chemicalreaction. The reaction that takes place is:

Mg(s) + 2HC (aq) MgC2 (aq) + H 2 (g)

The learners use the apparatus and follow the method shown below to conduct theinvestigation.

Method Experiment 1:Step 1: Place a spatula of magnesium powder in a conical flask and add 50 cm 3 HC(aq) of known concentration.Step 2: Simultaneously start the stopwatch and close the flask with the rubberstopper containing the delivery tube.Step 3: Measure the volume of the H2(g) formed in time intervals of 20 seconds.

Method Experiment 2:Repeat steps 1 to 3 above, but use only 25 cm 3 of the same HC aq) diluted to 50cm 3 with distilled water.

Apparatus:

1.1 How does the concentration of the acid used in Experiment 2 differ from theconcentration of the acid used in Experiment 1? Write down only GREATERTHAN, SMALLER THAN or EQUAL TO. (1)

1.2 Write down a hypothesis for this investigation. (2)

1.3 Why should the learners ensure that equal amounts of magnesium powderare used in each of the two experiments? (2)


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1.4 The learners use an excess of HC aq) for the two experiments. Give a reasonwhy the excess HC aq) will not influence the results. (2)

After completing the investigation, the learners represent the results obtained duringeach experiment on the graph below.

1.5 Write down the volume of hydrogen gas formed during the first minute in:Experiment 1Experiment 2 (2)

1.6 Which one of the experiments (Experiment 1 or Experiment 2) took place atthe faster rate? Refer to the shape of the curves to motivate your answer.

(2)

1.7 Give a reason why the final volume of gas produced is the same in both

experiments. (1)

1.8 What conclusion can the learners draw from the results obtained? (2)

1.9 How will an increase in the temperature influence the following:a) Final volume of gas obtained in each experiment (1)(Write down only INCREASES, DECREASES or REMAINS THE SAME.)

b) Volume of gas obtained in each experiment after 40 s (1)(Write down only INCREASES, DECREASES or REMAINS THE SAME.)


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Question 2Diagrams P, Q and R represent different reaction mixtures of the followinghypothetical reaction that is at equilibrium in a closed container at a certaintemperature.

X(g) + Y 2(g)

XY(g) + Y(g) H > 0

If at equilibrium the K c = 2, which diagram(s) correctly represent(s) the mixture atequilibrium?A P onlyB Q onlyA R onlyA P, R and Q (2)

Question 3The thermal decomposition of calcium carbonate (CaCO3) is an example of aheterogeneous equilibrium. The decomposition that takes place in a closed containercan be represented by the following equation:

CaCO 3(s) CaO(s) + CO 2(g)

Initially 5 g of CaCO 3(s) is placed in a closed 500 cm 3 container and then heated.Equilibrium is reached at 900 C.

3.1 Why is the above decomposition referred to as a heterogeneous equilibrium?(1)

3.2 Calculate the mass of unreacted CaCO3(s) that remains in the container atequilibrium if Kc for the reaction is 0,0108 at 900 C. (9)

3.3 It is found that the value of Kc increases when the container is heated to ahigher temperature. Is the forward reaction exothermic or endothermic? UseLe Chatelier's principle to explain your answer. (3)

3.4 The volume of the container is now decreased to 250 cm3 while thetemperature is kept constant. How will each of the following be affected?Write down only INCREASES, DECREASES or REMAINS THE SAME.

The value of Kc (1)a) The number of moles of CaCO 3(s) present in the equilibrium mixture (1)

b) The concentration of CO 2(g) at the new equilibrium (1)


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3.5 More CaCO 3(s) is now added to the equilibrium mixture in the 500 cm 3 container. How will this change influence the number of moles of CO 2(g)?Write down only INCREASES, DECREASES or REMAINS THE SAME. (1)

Question 42 mol of NO 2(g) and an unknown amount of N 2O4(g) are sealed in a 2 dm 3 container,that is fitted with a plunger, at a certain temperature. The following reaction takesplace:

2NO 2(g) N2O4(g)

At equilibrium it is found that the NO2 concentration is 0,4 moldm-3. The equilibriumconstant at this temperature is 2.

4.1 Calculate the initial amount (in mol) of N 2O4(g) that was sealed in thecontainer. (9)

The plunger is now pushed into the container causing the pressure of the enclosedgas to increase by decreasing the volume.

4.2 How will this change influence the amount of nitrogen dioxide at equilibrium?Only write down INCREASES, DECREASES or REMAINS THE SAME. (1)

4.3 Use Le Chatelier's principle to explain your answer to 4.2 (2)


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Topic 3: Redox & Chemical Industries

Question 1Batteries consist of one or more galvanic cells. A galvanic cell is a combination oftwo half-cells. Phil wants to determine which one of Options A or B, shown below,can be used to assemble a galvanic cell with the highest potential difference.

Option Combination of half-cells

A Ag(s) in AgNO 3(aq) & Ni(s) in Ni(NO 3)2(aq)

B Mg(s) in Mg(NO 3)2(aq) & Ag(s) in AgNO 3(aq)

1.1 Draw a fully labelled diagram of the galvanic cell that Phil can use to

measure the potential difference for the cell in Option B . Use a positive (+)and negative (-) sign to indicate the positive and negative electrodesrespectively. (5)

1.2 Write a balanced chemical equation, excluding spectator ions, for the net(overall) cell reaction for the galvanic cell in Option B. (3)

1.3 Calculate the initial potential difference that can be obtained understandard conditions for the galvanic cell in Option B. (4)

1.4 State TWO standard conditions that John must adhere to during the

experiment, to ensure that the measured potential difference is the sameas the calculated potential difference. (2)

1.5 Write down the cell notation (symbolic notation) for the galvanic cell inOption A . (3)

1.6 WITHOUT ANY CALCULATIONS, determine which one of Option A orOption B should result in the galvanic cell with the highest potentialdifference. Refer to the relative strengths of the two reducing agentsinvolved, as well as the relative strengths of the two oxidising agentsinvolved, to explain your answer. (3)

Question 2Electrolysis is an important industrial process used to decompose compounds,extract metals from their ores and to purify metals like gold or copper.The simplified diagram below represents an electrolytic cell used to purify copper.


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2.1 Define the term electrolysis. (2)

2.2 Which electrode, P or Q, consists of the impure copper? Explain how youarrived at your answer. (3)

2.3 Write down the half-reaction that takes place at electrode Q. (2)

2.4 During purification, metals such as silver and platinum form sludge at thebottom of the container. (2)

2.5 Refer to the relative strengths of reducing agents to explain why these twometals do not form ions during the purification process. (2)

2.6 Explain why the concentration of the copper(II) sulphate solution remainsconstant. Assume that the only impurities in the copper are silver andplatinum. (2)

2.7 Why is the sludge of economic importance? (2)

Question 3The diagram below is a simplified version of a membrane cell, one of the electrolyticcells used in the chlor-alkali industry. The letters P and Q represent the two gasesformed during this process.

3.1 Write down the letters P and Q and next to each letter, write down the half-reaction that shows how gas P and gas Q are respectively formed. (4)

3.2 Water (H 2O()) and sodium ions (Na+(aq)) are both present in the cathode side ofthe membrane cell. Explain why hydrogen gas, and not sodium metal, is formed

in the membrane cell. Refer to the relative strengths of oxidising agents to explainyour answer. (2)

3.3 State ONE function of the membrane. (1)

Question 4Some cells, such as the nickel-cadmium cell used in calculators and electric shavers,can be recharged. Others, such as those used in watches and torches, cannot berecharged.

4.1 Are rechargeable cells primary or secondary cells? (1)

The half-reactions occurring in a nickel-cadmium cell are shown below:


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Cd(s) + 2OH- (aq) Cd(OH)2 (s) + 2e - (I)

NiO2(s) + 2H 2O( ) + 2e- Ni(OH)2(s) + 2OH -(aq) ..(II)

The emf of the nickel-cadmium cell is 1,4 V.

4.2 Which ONE of these half-reactions occurs at the cathode? Give a reason foryour answer. (2)

4.3 Write down the balanced equation for the overall cell reaction. (3)

4.4 Calculate the maximum work done by the cell under standard conditions as 1mol of Cd is used up.(NOTE:1 mole of electrons has a charge of 9,65 x 10 4 C.) (4)

Question 5 About one third of the protein consumed by humans comes from fertilisers. Theflow diagram below shows three industrial processes, A, B and C, that result inthe production of fertilisers.

5.1 Write down the name of the Process A. (1)

5.2 Write down the balanced equation for the reaction which takes place inProcess B. (3)

5.3 Write down the balanced equation for step 2 of Process C. (3)

5.4 Write down the FORMULA and the NAME of product X in step 3 of Process C.(2)

5.5 Write the FORMULA and the NAME of the fertiliser represented by Y. (3)

Process B

Process C

Contact process

Step 1: S + O 2 SO2 Step 2: _________________

Step 3: SO 3 + H2SO 4 X Step 4: X + H2O H2SO 4

H2SO 4

Y

H2

Process A

N2

NH3


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5.6 Fertiliser prices increased by more than 200 per cent since 2007. This rise isfuelled by new demand.

5.6.1 Give TWO reasons why there is a continuous demand for fertilisers.(2)

5.6.2 Give TWO reasons why there is an increase in the price of fertilisers.(2)


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SolutionsTopic 1: Organic Chemistry

Question 11.1.1 Carboxylic acids

1.1.2 Alcohols

1.1.3 Aldehydes

1.2.1 Propanal

1.2.2 Pentan-1-ol

1.3 OPTION 1Relationship: Boiling point and type of functional group/homologousseries What is the relationship between boiling point and the type of functional group

/ type of homologous series? ORHow do the boiling points of compounds from the three homologous seriesdiffer / compare?OPTION 2 Relationship: Boiling point and chain length / molar mass/ molecularsize (of compounds with same functional group / from same homologousseries).What is the relationship between boiling point and chain length / molar mass /

molecular size? ORHow does chain length / molar mass / molecular size influence boiling point?

1.4 If Option 1 in Question 5.3Molar mass / molecular mass / formula massIf Option 2 in Question 5.3Type of functional group / homologous series

1.5 Option 1: Molecules with different functional groups have different boilingpoints. More polar molecules have higher boiling points

Option 2: An increase in the length of a molecules chain increases theboiling point

1.6 Boiling point of carboxylic acids > alcohols > aldehydes.


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Question 22.1 Contains a double bond (between two carbon atoms).

2.2

2.3 Addition / hydrohalogenation / hydrobromination

2.4Propan-2-ol

2.5 Hydrolysis

2.6.1 Water

2.6.2 H3PO

4 / H

2SO

4

2.6.3 Addition / hydration

2.7.1 prop-1-ene

2.7.2 Dehydrohalogenation OR Elimination

Question 33.1 Compounds that have the same molecular formula but different structural

formulae.

3.2methylmethanoate

ethanoic acid

3.3.1 Ethanoic acidThe hydrogen bonds/intermolecular forces between ethanoic acid moleculesare stronger than the Van der Waals forces/intermolecular forces between

the ester molecules.More energy needed to break bonds between ethanoic acid molecules


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3.3.2 MethylmethanoateThe Van der Waals forces/intermolecular forcesmolecules are weaker than the hydrogen bonds/ intermolecular forcesbetween ethanoic acid moleculesLess energy needed to break bonds between the ester molecules.

3.4 Decrease: Van der Waals forces increase with molecular size

Question 44.1 Alcohols

4.2

4.3 Catalyst4.4 Ethanol is flammable.

4.5 Vapours are cooled down and condense / return to the test tube.

4.6 Sodium carbonate solution is a base and will neutralise both acids, preventingthem from masking the smell of the ester

4.7 Boiling point OR Vapour pressure


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Solutions Topic 2: Rates & Chemical Equilibrium

Question 11.1 Smaller than

1.2 Criteria for hypothesis:Refers to relationship between dependent and independent variables.Statement that can be proved correct or incorrect. prediction based on (prior) knowledge.Examples:Reaction rate (or volume of hydrogen gas produced per unit time)Increases (decreases) with increase in concentration

The higher the concentration (of HC!) the faster the rate of thereaction. (2)

1.3 To make a fair comparison / test. (or)Magnesium is a controlled variable (or)To ensure that there is only one independent variable (concentration). (2)

1.4 Magnesium is the limiting reagent. / When Mg is used up, the reaction willstop / The same amount (mass/volume) of Mg will react with the sameamount of acid in each experiment.

1.5 Experiment 1: 60 cm 3 Experiment 2: 42 cm 3

1.6 Experiment 1: The gradient / slope (of tangent to graph) is steeper.

1.7 The number of moles / amount / mass of Mg used in both experimentswere the same.

1.8 Reaction rate increases with increase in concentration orReaction rate (volume of hydrogen gas formed per unit time)decreases with decrease in concentration.

1.9 Final Volume : Remains the same

At 40s: Increases

Question 2Solution: BIn Q the number of molecules: Number of Y = 2 Number of XY = 4

Number of X = 2 Number of Y 2 = 2

Kc =XY. YX . =

4 . 22 . 2 = 2


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Question 33.1 Reactants and products are in different phases i.e the reactant CaCO 3 and

one of the products CaO are solids and the other product CO 2 is a gas.

3.2 Multiple options

Kc = CO2 0,0108 = [CO2][CO2] = 1,08 x 10 -2moldm -3

n(CO2) = cV = (1,08 x 10 -2) (0,5) = 5,4 x 10-3mol

n(CaCO3)used = n(CO2) n(CaCO3)used = 5,4 x 10 -3molm(CaCO3)used = nM

= (5,4 x 10- 3)(100) = 0,54 g

Mass at equilibrium = 5 0,54= 4,46 g

3.3 Endothermic According to Le Chatelier's principle an increase in temperature willfavour the endothermic reaction. / the reaction that uses energy. When T was increased, Kc increased, therefore [CO2] increased / moreproducts form, therefore forward reaction was favoured.

3.4 Kc : Remains the samemoles of CaCO 3: IncreasesConcentration of CO 2: Remains the same

3.5 The number of moles of CO 2(g): Remains the same

Question 44.1 2NO2 N2O4Ratio from balanced equation: 2 1Initial number of mole (mol) 2 xNumber of moles used/formed (mol) - 1,2 +0,6 Number of moles at equilibrium(mol) 0,8 x + 0,6 Equilibrium concentration (moldm -3) 0,4 (x + 0,6) 2 Kc =

2 = 0,4 x = 0,04 mol

4.2 Decreases

4.3 When the pressure is increased the system will try to decrease thepressure. The forward reaction (2 mol to 1 mol) is favoured.


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Solutions Topic 3: Redox & Chemical Industries

Question 11.1

1.2 Mg(s) + 2Ag +(aq) Mg2+(aq) + 2Ag(s)

1.3 anode

cathode

cellEEE

= 0,80 (- 2,36)= 3,16 V

1.4 Ensure a temperature of 25 C and solutions of concentration 1 moldm -3

1.5 Ni(s) | Ni 2+ (1 mol.dm -3) || Ag + (1 mol.dm -3 | Ag(s)

1.6 Option BThe reaction leading to the highest emf (or potential difference) will bebetween the strongest reducing agent (Mg) and the strongest oxidisingagent (Ag +).

Question 22.1 The process in which electricity is used to bring about a chemical change /

decompose/break compounds into components. (A process in which electricalenergy is converted to chemical energy. )

2.2 P Reason: P is the electrode at which oxidation takes place (anode) Copperatoms loose electrons to form copper ions at this electrode.

2.3 Cu 2+(aq) + 2e - = Cu(s)

2.4 4Pt and Ag are both weaker reducing agents (than copper) and will notbe oxidised. OR Cu is a stronger reducing agent (than Pt and Ag) and will beoxidised.

2.5 The rate at which copper is oxidised (at the anode) is equal to the rateat which copper ions are reduced (at the cathode)

2.6 Contains valuable / expensive metals. Or Platinum and silver are valuable /

expensive metals.


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Physical Sciences P2 Learner Guide July 2011