Cambridge Assessment International Examination Chemistry · 2020. 10. 23. · Cambridge Assessment International Examination O Level 7RSLFDO 3DSHU Chemistry 700+ Theory Question with

Cambridge Assessment International Examination

O Level Topical Paper 2Chemistry

700+ Theory Question with Mark Scheme

2005-2019 Compiled By:

NIAZ AHMED AWAN [email protected] +923004255956 Senior A Level Chemistry at Lahore Grammar School

Visiting Faculty Member at: Beaconhouse (Newlands & JT Campuses) LGS, KIMS, The City School, SICAS, LACAS

Endorsed By: ZAHID IQBAL WARRAICH Senior A Level Chemistry Teacher

UMAR ZAMAN KHATTAK HOD: Garrison Academy for Cambridge Studies

NOUMAN AHMAD A Level Chemistry Teacher at: Aitchison College, Lahore

MUHAMMAD SAQIBChemistry Teacher at: Lahore Grammar School JTC MUHAMAD ASHFAQ O & A Level Chemistry Teacher at: LACAS, LGS, Lahore Lyceum

SHAHBAZ YASEEN O & A Level Chemistry Teacher at: LACAS, Johar Town

HAMID MAHMOOD Beaconhouse Palm Tree Campus Gujranwala.+92322-7126666

Content Cambridge Syllabus 2020-21………………………….. 5 Topic 1 Methods of Purification & Analysis………………… 19 Topic 1.1 Experimental Chemistry……………………………… 40 Topic 2.1 Kinetic Particle Theory……………………………….. 48 Topic 2.2 Atomic Structure………………………………………. 55 Topic 2.3 Structure and Properties of Material………………. 90 Topic 2.4 Chemical Bonding…………………………………… 105 Topic 3: Formulae, Stoichiometry & the Mole Concept….. 121 Topic 4 Electrolysis……………………………………………. 192 Topic 5 Energy from Chemicals…………………………….. 233 Topic 6.1 Rate of Reaction……………………………………… 275 Topic 6.2 Redox Reaction………………………………………. 316 Topic 7 The Chemistry and uses of Acids………………… 334 Topic 8 Periodic Table 392 Topic 9 Metals 428 Topic 10 Atmosphere and Environment 476 Topic 11 Organic Chemistry 515 Topic 11.1 Alkanes 607 Topic 11.2 Alkenes 620 Topic 11.4 Carboxylic Acids 631 Topic 11.5 Polymers 647 Topic 12 Miscellaneous Question (Mixed) 662

November 2018 and June 2109 684

Red grapes contain a number of coloured pigments. Some red g rapes are cr ushed and the pigments e xtracted with a solv ent. The deep red

solution contains a mixture of pigments. (a) Name the technique used to separate the pigments in this mixture and dr aw a labelled

diagram of the apparatus you would use.

name of technique ...........................................................................................................

Sorrel is a small green plant.

(b) The pigments in the sorrel leaf can be separated by chromatography.

(i) Describe how chromatography can be used to separate different pigments.

[2]

(ii) Explain what is meant by R value.

[1]

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(c) Proteins are hydrolysed to give a mixture of colourless amino acids.

Describe, with the aid of a labelled diagram, how paper chromatography can be used to

identify the amino acids present in a mixture of amino acids.

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Proteins are naturally occurring macromolecules.

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Topic 1. Methods of Purification & Analysis 5054 Chemistry Topical Paper 2

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Seawater contains a variety of dissolved salts. (d) The diagram shows a simple distillation apparatus that can be used to produce purified water

from seawater.

seawater

water out

water inheat

purified water

condenser

Explain how distillation purifies seawater.

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(a) is an insoluble yellow solid.

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Choose from the following substances to answer the questions below.

aluminium oxideammonia

barium sulphatecalcium carbonate

carbon monoxidelead(II) iodide

nitrogen dioxidesilicon dioxide

Each substance can be used once, more than once or not at all.Name a substance which

Chlorine, hydrogen and sodium h ydroxide are made b y the electrolysis of concentr atedaqueous sodium chloride.

(b) Describe a chemical test f or each of the gases produced dur ing the electrolysis of

concentrated aqueous sodium chloride.

(i) chlorine

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(ii) hydrogen

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(c) reacts with chlorine to form a solid that dissolves in water to give a coloured solution.

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Choose from the following elements to answer the questions below.aluminium

argoniron

nickelnitrogen

phosphorussodium

Each element can be used once, more than once or not at all.

Name an element which

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(a) (i) Describe a chemical test to show the presence of the nitrate ion.

[2]

(ii) Suggest why it might be difficult to test f or the presence of the nitrate ion in a sample of

river water.

[1]

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River water contains many substances including minerals, dissolved oxygen, organic material,nitrates and phosphates.

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(b) A sample of powdered brass is added to excess dilute nitric acid.

The mixture is heated gently until all the brass reacts.

The resulting solution, A, contains aqueous copper(II) ions and aqueous zinc ions.

(i) Suggest the colour of solution A.

[1]

(ii) Describe and explain, with the aid of equations , what happens when aqueous sodiumhydroxide is slowly added to solution A.

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Brass is an alloy containing zinc and copper.

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(i) any two of:

• chromatography paper (with bottom of paper) in solvent ALLOW: diagram showing this with solvent clearly labelled and paper dipping into

solvent ALLOW: named solvent

• spot of mixture put (on line) ALLOW: diagram showing this NOT: diagrams showing original spot/base line below solvent level

• allow solvent to move up paper/pigments are separated as they move (vertically) up the paper

ALLOW: separated pigments on a diagram vertically aligned NOT: single pigments originating from different spots on the base line

[2]

distance spot moves ÷ distance of solvent front from base (starting) line

ALLOW: diagrams

[1]

ALLOW: distance moved by substance ÷ distance moved by solvent ALLOW: the ratio of the distance moved by the spot/substance to that moved by the

solvent NOT: the ratio of the distance moved by the solvent to that moved by the spot/substance

(c) Chromatography paper dipped into the solvent (1) ALLOW: chromatography paper just touching solvent (there should be no space between the solvent and the bottom of the paper)

Spot of mixture on paper above the level of the solvent labelled appropriately e.g. mixture / amino acid / amino acids / spot of amino acid / drop from sample (1)

Use of a locating agent to view the spots / amino acids / use of ninhydrin to view spots / amino acids (1)

NOTE: this must be after the chromatography

Comparing Rf values with known amino acids / compare with height of spots from known amino acids run at the same time (1) [4]

water and salts have different boiling points (1) water evaporates AND salts / residues / impurities / solids left in flask (1) water condenses / turns to liquid in the condenser (1) [3]

(b)


NIAZ AHMED AWAN ([email protected])

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lead(II) iodide

chlorine bleaches litmus or turns starch/iodide paper blue (1)

(ii) hydrogen pops with a burning splint (1)

iron or nickel

(a)

(b)

(c)

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(i) either add Al and NaOH and warm NH3 turns litmus blue

or add conc. H2SO4 and FeSO4 brown ring forms (2)

(ii) nitrate ion too dilute (1)

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(i) colour is blue (1) (ii) any 5 of:

• blue precipitate;

• Cu2+ + 2OH- → Cu(OH)2

ALLOW: full equation • white precipitate masked by blue one/ ppt lighter blue in colour than with copper

hydroxide alone • Zn2+ + 2OH- → Zn(OH)2

ALLOW: full equation

• precipitates are copper hydroxide and zinc hydroxide or correct

formulae (can be from the equations) • part of the precipitate redissolves in excess (sodium hydroxide)/ ppt of zinc hydroxide

redissolves in excess (sodium hydroxide) (i) names: B is zinc chloride (1)

C is copper (1) (ii) ionic equation (1) Zn + 2 H+ → Zn2+ + H2

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(b)

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Aqueous hydrochloric acid contains chloride ions.

Describe a test for chloride ions.

test ............................................................................................................................................

result .....................................................................................................................................[2]

Both zinc and iron react with dilute sulfuric acid.

Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(g)

Fe(s) + H2SO4(aq) FeSO4(aq) + H2(g)

(a) A 0.65 g sample of zinc is reacted with excess sulfuric acid.

(i) Calculate the volume of hydrogen, measured at room temperature and pressure, formed in this reaction.

volume of hydrogen = .................................................. dm3 [2]

(ii) Explain why a different volume of hydrogen, measured at room temperature and pressure, is formed when 0.65 g of iron is reacted with excess sulfuric acid.

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Topic 1.1 Experimental Chemistry 5054 Chemistry Topical Paper 2

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(b) A mixture of iron powder and zinc powder is added to excess sulfuric acid.

When the reaction stops, aqueous sodium hydroxide is added drop by drop to the reaction mixture until it is in excess.

Describe what you would observe during the addition of aqueous sodium hydroxide and explain the reactions taking place.

observations

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explanations

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(c) The products of heating iron(II) sulfate are iron(III) oxide, sulfur dioxide and sulfur trioxide.

(i) Explain how you can tell that the reaction involves an oxidation.

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(ii) Describe the chemical test for sulfur dioxide.

test ....................................................................................................................................

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observation ........................................................................................................................

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Manganese(IV) oxide, MnO2, can be used in the preparation of both chlorine and oxygen.

Reaction 1 MnO2(s) + 4HCl(aq) Cl2(g) + 2H2O(l) + MnCl2(aq)

Reaction 2 2H2O2(aq) O2(g) + 2H2O(l)

In reaction 2 manganese(IV) oxide acts as a catalyst.

(a) Reaction 1 converts chloride ions into chlorine molecules.

Explain why this is an example of oxidation.

...................................................................................................................................................

.............................................................................................................................................. [1]

(b) Reaction 1 is investigated using different masses of MnO2. The results are shown in the table.

volume of HCl / cm3

concentration of HCl (aq) in mol / dm3

mass of MnO2 used

/ g

volume of Cl2 formed at room temperature and pressure

/ dm3

100 1.0 1.74 0.48

100 1.0 0.87 0.24

Explain the difference in the volume of chlorine formed.

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(c) Reaction 2 is investigated using different masses of MnO2. The results are shown in the table.

volume of H2O2(aq)

/ cm3

concentration of H2O2

in mol / dm3

mass of MnO2 used

/ g

volume of O2 formed at room temperature and pressure

/ dm3

100 1.0 1.74 1.20

100 1.0 0.87

Predict the volume of oxygen, measured at room temperature and pressure, when 0.87 g of MnO2 is used. Write your answer in the table. [1]

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add nitric acid and silver nitrate (1) [2] white precipitate / white solid formed (1)

1

Moles of Zn and H2 = 0.01 (1) Volume of H2 = 0.24 dm3 (1)

2

The number of moles of iron is different (1) 1

One mark each for any two observations from: Solution gets warmer / heat given off (1) White precipitate formed (1) which redissolves in excess (1) Green precipitate formed (1) With excess the green precipitate remains (1) One mark each for any two explanations from Acid is neutralised (1) Green precipitate is iron(II) hydroxide (1)

White precipitate of zinc hydroxide (1) which will redissolve in excess (1)

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Oxidation number of iron increases / oxidation number of iron becomes more positive / iron(II) ions lose electrons (1)

1

Use (filter paper dipped into acidified) potassium manganate(VII) (1) Purple colour changes to colourless (1)

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2 (a) (i)

(ii) (b)

(c) (i)

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Chloride ions lose electrons / oxidation state of chlorine increases or gets more positive / oxidation state (of chlorine) goes from –1 to 0 / the chloride loses hydrogen (1)

1

Idea that manganese(IV) oxide is limiting reagent / HCl(aq) is in excess (1) The volume of gas is proportional to the mass of MnO2 / As the mass of MnO2 increases, the volume of gas increases / There is a positive correlation between (the mass of) MnO2 and the (volume of) chlorine (1)

2

(1) 1

Iron(II) chloride gives a green precipitate / Iron(II) chloride gives a grey-green

precipitate (1)

Iron(III) chloride gives a brown precipitate (1)

Fe2+ + 2OH– → Fe(OH)2 / FeCl 2 + 2NaOH → Fe(OH)2 + 2NaCl (1) Fe3+ + 3OH– → Fe(OH)3 / FeCl 3 + 3NaOH → Fe(OH)3 + 3NaCl (1)

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(Moist blue or red) litmus paper (1) Bleached / goes white (1)

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5070/02/O/N/07/Q2 A student set up the apparatus shown below.

YX

cotton wool soaked inconcentrated hydrochloricacid

cotton wool soaked inconcentrated aqueous ammonia

Colourless fumes of hydrogen chloride are given off by the hydrochloric acid. Colourless fumes of ammonia are given off by the aqueous ammonia.

(a) After a few seconds, white fumes were seen at point X in the tube. Name the compound formed at point X.

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(b) Use the kinetic particle theory to explain this observation.

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(c) The student repeated the experiment using a solution of methylamine, CH3NH2, in place of ammonia, NH3.

The white fumes were seen at point Y in the tube, rather than at point X. Explain this difference.

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Topic 2.1. Kinetic Particle Theory 5054 Chemistry Topical Paper 2

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Bromine is a liquid at room temperature.

(i) Draw a diagram to show the arrangement of the molecules in liquid bromine.

Show a bromine molecule as .

[2]

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3 (a)

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(d) Bromine is a liquid with a low boiling point and a strong smell. A technician spilt some bromine in the cor ner of a room which is free of dr aughts. After

thirty seconds the bromine could be smelt on the other side of the room.

bromine spillage

technician

Fig. 2

Use the kinetic par ticle theory to explain why the bromine could be smelt on the other side of the room.

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ammonium chloride [1]

ALLOW: NH4Cl NOT: ammonia chloride any 3 of the following: [3] • evaporation of hydrogen chloride and ammonia molecules or particles from cotton wool/ • diffusion OR diffusing/ • explanation of diffusion e.g. particles/molecules in (constant) movement/ • molecules OR particles collide/ NOT: ions OR atoms collide/ • hydrogen chloride heavier (than ammonia) or reverse argument/ ALLOW: hydrogen chloride denser (than ammonia) or reverse argument/ • hydrogen chloride moves slower than ammonia or reverse argument/ RMM of methylamine greater (than that of ammonia); [1] ALLOW: methylamine is heavier/denser ALLOW: ammonia is lighter ALLOW: methylamine has a similar RMM to hydrochloric acid methylamine moves slower than ammonia [1] ALLOW: HCl/methylamine diffuse/move at similar rates

explanation of evaporation e.g. particles (or molecules) with a lot of energy leave the liquid / bromine particles break free from each other / forces or bonds between bromine molecules broken; [1]

ALLOW: particles (or molecules) of bromine escape from liquid NOT: particles evaporate diffusion / diffuse; [1] REJECT: Brownian motion explanation of diffusion involving qualified movement of molecules / particles e.g. random movement of molecules / molecules move anywhere / molecules in (constant)

collisions / particles disperse / particles travel throughout the room / constant motion of the bromine particles; [1]

IGNORE: molecules move from area of high concentration to low concentration / particles move to the other side of the room

(i) molecules very close together; [1] molecules random/irregularly arranged; [1]

(ii) any 3 of: [3]

faster moving/more energetic molecules escape from liquid/

diffusion/

random movement of molecules/

molecules get mixed up with molecules in the air/

molecules of bromine collide with molecules in the air

(a)

(b)

(c)

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Iron is one of the most important metals. It is a transition element. Most iron is used in the alloy steel.

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At room temperature ozone decomposes slowly to form oxygen, O2.

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Ozone, O3, is an atmospheric pollutant in the lower atmosphere but is beneficial higher up inthe atmosphere.

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5070/02/M/J/05/Q7

A sample of a compound of iron is analysed. The sample contains 0.547g of potassium,0.195 g of iron, 0.252 g of carbon and 0.294 g of nitrogen.Calculate the empirical formula of this compound.

Answer .........................................................................................................................[3]

.[3]

The decomposition can be represented by the equation below. The reaction isexothermic. One mole of ozone will release 143 kJ when it is fully decomposed.

2O3 → 3O2

Calculate the energy released when 16 g of ozone is decomposed.

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Sunglasses can be made from photochromic glass. When bright light strikes photochromicglass it darkens.Photochromic glass contains small amounts of silver chloride, AgCl, and copper(I) chloride,CuCl.In the presence of br ight light, silver chloride decomposes into silver atoms which make theglass go dark, and into chlorine atoms.

AgCl → Ag + Cl

Chlorine atoms immediately react with copper(I) chloride to make copper(II) chloride.

CuCl + Cl → CuCl2When the exposure to br ight light ends, silver atoms reduce copper( II) chloride back intocopper(I) chloride and silver chloride.

(a) Calculate the maximum mass of silver that can be formed when 0.287g of silverchloride decomposes.

Topic 3: Formulae, Stoichiometry & the Mole Concept 5054 Chemistry Topical Paper 2

calculation for idea of dividing by correct Ar (1) dividing by the smallest (1) for final formula only if first 2 fully correct (1) K 0.547/39 Fe 0.195/56 C 0.252/12 N 0.294/14

0.0140 0.00348 0.0210 0.0210 4 1 6

i.e. K4FeC6N6 or K4Fe(CN)6 [3]

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calculation 48 g ozone releases 143 kJ (1) 16 g ozone releases 47.66 kJ or 47.7 kJ (1) (answer alone (1), units needed) (if 6 x 16 = 96 g ozone used, then (0)) (if 0.33 used, answer = 47.2) [6]

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calculation (2) 143.5 g AgCl contains 108 g Ag

0.287 g AgCl contains 0.216 g Ag (answer alone (1), units needed)

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MARK SCHEME Topic 3: Formulae, Stoichiometry & the Mole Concept 5054 Chemistry Topical Paper 2

Chlorine, hydrogen and sodium hydroxide are made by the electrolysis of concentratedaqueous sodium chloride.

(a) Aqueous sodium chloride contains the following ions, Na+, H+, OH– and Cl–.Concentrated aqueous sodium chloride can be electrolysed using inert electrodes.The electrode reactions are represented below.

cathode 2H+ + 2e– → H2

anode 2Cl– → Cl2 + 2e–

(i) Explain why hydrogen, not sodium, is formed at the cathode.

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(ii) Suggest why, as the electrolysis proceeds , the concentration of sodium hydroxide

in the electrolyte increases.

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Describe an advantage of using hydrogen as a possible fuel in the future.

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Chlorine, hydrogen and sodium h ydroxide are made b y the electrolysis of concentr atedaqueous sodium chloride.

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(b) (i) Give the formulae of all the ions present in the solution.

(ii) Write half equations for the reactions at the anode and cathode . Use the half equationsto construct an overall equation for the reaction and give tests for any gases evolved.

(iii) Use your equations to e xplain how the composition of the solution changes after theelectrolysis has been running for some time.

[6]

(c) Describe another method for making hydrogen from dilute sulphuric acid. Your answer should

include names of the reagents you use and an equation for the reaction.

[2]

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A student carried out an electrolysis of dilute sulphuric acid and collected the gases formed. (a) Draw a labelled diagram to show the apparatus used.

[2]

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(i) hydrogen is below sodium in the reactivity series (1) (ii) chloride ions are removed (leaving hydroxide ions) (1) [2]

burning hydrogen does not produce pollutants or only forms water or hydrogen is not a finite resource, is renewable [1]

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apparatus with battery and graphite electrodes; test tubes to collect gases no labels max 1

H+ OH- SO42-

2H+ + 2e-� H2 AND 4OH- � O2 + 2H2O+ 4e- ;

4H+ + 4OH- � 2H2 + 2O2 + 2H2O;

oxygen relights a glowing splint; hydrogen pops when lit;

Acid becomes more concentrated

React with more reactive metal e.g. Mg or Zn; M + H2SO4� H2 + MSO4;

1

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(a)

(b)

(a)

(c)

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Ozone, O3, is an atmospheric pollutant in the lower atmosphere but is beneficial higher up inthe atmosphere.

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In terms of the energy changes that take place dur ing bond breaking and bondmaking, explain why this reaction is exothermic.

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Draw an energy profile diagr

•• the activation energy,• the enthalpy change.

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In the presence of light methane reacts with chlorine.

CH4 + Cl2 → CH3Cl + HCl ∆H = –99.5 kJ


am for this reaction. Show:

•

the reactants and products,

• the activation energy,• the enthalpy change.

[3]

reaction pathway

energy

Methane, CH4, is the major constituent of natural gas.

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energy

progress of reaction

N2(g) + O2(g)

2NO(g)

energychange

X

energychange

Z

(a) Identify the energy changes X and Z.

[2]

(b) The reaction between nitrogen and oxygen is endothermic. (i) Explain how you can tell from the diagram that the reaction is endothermic.

[1]

(ii) Explain, using ideas about bond breaking and bond making, wh y the overall reaction is endothermic.

[3]

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The diagram shows the energy profile for this reaction.

Oxides of nitrogen are atmospher ic pollutants. Nitrogen monoxide, NO, is formed in an inter nal combustion engine when nitrogen and oxygen react together.

N2(g) + O2(g) 2NO(g)

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bond breaking is endothermic/absorbs energy (1) and bond forming is exothermic/releases energy more energy released than absorbed (only if first point scored) (1)

reactants on left and products on right; product level below reactant level and ∆H correctly labelled; activation energy correctly labelled; [3]

X = activation energy; [1] ALLOW: Ea Z = enthalpy change (of reaction); [1] ALLOW: ∆H NOT: energy change/heat given out

(b) (i) energy change is positive/enthalpy change is positive/ energy of 2NO is above that of N

2 and O

2/

energy of N2 and O2 is below that of 2NO/ energy of product(s) is above that of reactants/ energy of reactants is below that of product(s) [1] NOT: it (unspecified) gains energy NOT: the product is above the reactants

(ii) bond breaking is endothermic/absorbs energy/takes in energy; [1] bond making is exothermic/releases energy/gives out energy; [1] more energy is absorbed than released [1] [NOTE: 3rd mark can only be scored if first two marks have been gained] REJECT: answers in terms of energy involved in bond making/breaking [more energy absorbed in bond breaking than release in bond making OWTTE = 3 marks]

(i) activation energy lowered/provides surface for molecules to react/makes the reaction go by quicker alternative pathway NOT: allows more frequent collisions [1]

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2

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(a)

MARK SCHEME Topic 5 Energy from Chemicals 5054 Chemistry Topical Paper 2

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Cambridge Assessment International Examination Chemistry · 2020. 10. 23. · Cambridge Assessment International Examination O Level 7RSLFDO 3DSHU Chemistry 700+ Theory Question with