UNIVERSITY OF MALTA

SECONDARY EDUCATION CERTIFICATESEC

CHEMISTRYMay 2011

MARKING SCHEME

MATRICULATION AND SECONDARY EDUCATIONCERTIFICATE EXAMINATIONS BOARD

1

Marking scheme – May 2011 Paper 1 Section A 1 boils

increases steam dissolves solvent solute electricity

1 1 1 1 1 1 1

Total 7 marks 2 (a) incomplete dissociation / ionization of the molecules ½

Accept produces few H+ ions in solution / in water ½

1

(b) (i) sodium chloride/ potassium sulfate 1 (ii) ammonia solution

do not accept zinc oxide 1

(c) In water H+ /H+ (aq)/ H3O+ (aq) Cl- / Cl- (aq)

ignore ions from water

½ ½

In methylbenzene HCl

DO NOT accept HCl (aq)

1

Total 5 marks 3 (a) Mg + 2HCl →MgCl2 + H2

all symbols correct award 1 balancing correct award 1

2

(b) gas syringe or syringe / calibrated gas jar / inverted measuring cylinder

Do not accept measuring cylinder

1

(c) (i) Moles HCl = 20/1000 x 0.15 ½ = 0.003 ½

1

(ii) 2 moles HCl : 1 mole H2 ½ moles H2 = 0.0015 ½ Vol H2 = 0.0015 x 22.4 ½ = 0.0336 dm3 ½ Accept 0.034 dm3 If not all the steps are shown, but some of the steps leading to a correct answer, award the 2 marks

2

Total 6 marks

2

4 (a) Structure of methoxymethane, CH3OCH3

1

(b) Formula or structure of organic product

(i)

C3H7OH + concentrated H2SO4

C3H6 or structure

(ii)

C3H7OH + sodium metal

C3H7ONa/ C3H7O- Na+ or structure

(iii)

C3H7OH + PCl5

C3H7Cl or structure

1 1 1

(c)

white fumes/ white misty fumes / fumes Do not accept effervescence

1

Total 5 marks 5. (a) (i) conc H2SO4 + KCl(s) →KHSO4 (s) + HCl(g)

all correct formulae award 1 do not accept K2SO4

correct state symbols award 1

2

(ii) Forms dense white fumes (½) with ammonia (½)/ forms fumes of ammonium chloride (½) with ammonia (½) / turns moist blue litmus (½) red (½).

Accept white ppt with AgNO3

1

(b) (i) hydrogen is lost/ oxidation state of chloride (or chlorine) is

increased/ oxidation state of Mn(IV) is reduced / Cl- lost electrons accept half-equation

1

(ii) bleaching of hair/ swimwear/ skin conditions/ respiratory problems/ etc bleaching associated (½) with presence of HOCl (½) / medical conditions (½) associated with HOCl (½)

1 1

Total 6 marks 6. (a) High pressure

low temperature 1 1

(b) Solid CO2 : weak intermolecular forces or Van der Waals forces

Diamonds: macromolecular structure Strong / covalent bonds (½) need to be broken (½)

1 1

(c) diamond: compact while graphite: layered / hexagon structure ½ x 2

OR diamond: 4 bonds per C atom; graphite 3 bonds per C atom ½ x 2 OR diamond : no delocalized e-s ; graphite delocalized e-s ½ x 2

1 1

Total 6 marks

3

7 (a) (i)

carbon dioxide/ CO2 1

(ii) Turns lime-water milky

1

(iii) Ba2+ (aq) + SO42-(aq) → BaSO4(s)

Sulfate ion identified 1 Ionic equation correct and all state symbols correct award 1

2

(b) (i) cation in Q is Al3+ / Zn2+

if charge is missing award ½ 1

(ii) cation in T is Pb2+ if charge is missing award ½

1

Total 6 marks

8 (a) (i) moles Na = 2.3/23 ½ = 0.1 ½

if not all steps are shown but answer correct award 1

1

(ii) moles O2 = 1.12/ 22.4 ½ = 0.05 ½

if not all steps are shown but answer correct award 1

1

(iii) O2 : 2O 0.05 : 0.01 ½ moles oxygen atoms = 0.1 ½

1

(b) Na : O

0.1 : 0.1 ½ 0.1 : 0.1 ½ ratio Na:O = 1 :1 ½ E.F. = NaO ½

if not all steps are shown but answer correct award 2

2

(c) mass of E.F = 39 ½ Ratio formula mass to E.F. mass =2 ½ Chemical formula = Na2O2 1

if not all steps are shown but answer correct award 2

2

Total 7 marks

4

9 (a) cars / internal combustion engine 1 (b) (i) SO2 / CO2 / O3 / CH4 / CFCs 1 (ii)

Depending on the answer in (b)(i): power stations/ combustion of fossil / factories / volcanoes – SO2 cars / power stations/ combustion of fossil fuels / factories – CO2 cars / combustion of fossil fuels –O3 decomposition of organic material – CH4 Aerosols, refrigerants – CFCs

1

(c) Depending on the answer in (b)(i):

respiratory problems / acid rain / skin or eye irritation – SO2 greenhouse effect / global warming – CO2 respiratory problems – O3 greenhouse effect – CH4 depletion of ozone layer – CFCs

1

(d) CO + N2O → CO2 + N2 OR

2CO + 2NO → 2CO2 + N2 OR 4CO + 2NO2 → 4CO2 + N2

all symbols correct award 1 balancing correct award 1

2

Total 6 marks

10 (a)

to show eight electrons around each iodine atom ½ x 2 sharing of electrons shown in a reasonable manner 1

if proper sharing of electrons not shown do not award 1

2

(b) Weak (½) intermolecular forces (½) or Van der Waals’ forces 1 (c) a lattice (½) of positive ions (½)

delocalized electrons/ sea of electrons/ free electrons from outer shells award 1

If diagram is correct but no labeling given award 1

2

(d) Copper contains mobile/delocalized electrons award ½

iodine has no free ions/ no free electrons/ is covalent award ½ 1

Total 6 marks

5

Section A 11 (a) (i) (orange or yellow) / (smoky or sooty) / luminous any two 1 x 2

Do not accept bright flame high C:H ratio / unsaturated / presence of triple bond

2 1

(ii) 2C6H14 + 13 O2 → 12CO + 14H2O

all symbols correct award 1 balancing correct award 1

2

(iii) C6H14 1 C9H18 1

2

(iv) propene 1

reasonable structure showing the double bond 1 if structure incorrect but double bond shown award ½

2

(b) (i) Substitution / free-radical substitution

Do not accept halogenation or chlorination 1

(ii) C2H6 + Cl2 → C2H5Cl + HCl

accept products CH3CH2Cl + HCl all symbols correct award 2

Formula of ALL products correct but formulae of reactants incorrect

award 1 Accept correct multiple substitutions

2

(iii) UV / diffused sunlight / light / photo-catalyzed Accept heat but not high temperatures

1

(c) (i) Any valid representation of CH3CHClCH2Cl

all bonds shown award 1 if more than 2 atoms missing in the structure award ½

1

(ii) addition reaction 1 (d) (i) addition of several monomers (½) with no loss of any atoms (½) 1 (ii) Any reasonable representation showing two units only

if {two units}n is given award ½ 1

(iii) No It is not biodegradable/ resistant to chemicals/ lasts for a long time/ animals may ingest it after granulation

1 1

(iv) bottles/ packaging/ toys/ construction materials/ piping/ wire coatings / plastic bags

Do not accept plastic

1

Total 20 marks

6

12 (a) (i) N2 + 3H2 2NH3 all symbols correct award 1 balancing correct award 1 but if sign not shown award 1 ½

2

(ii) 400 - 500 oC

200 – 350 atmospheres 1 1

(b) (i) Pt and Rh catalyst 1 (ii) 2NO(g) + O2(g) 2NO2(g)

all symbols correct award 1 balancing correct award 1 Ignore if not shown 4NO2 + 2H2O + O2 → 4HNO3 OR 2NO2 + H2O → HNO3 + HNO2

all symbols correct award 1 balancing correct award 1

2 2

(c) (i) ΔH is change in (½) enthalpy/ energy / heat (½)

represents dynamic equilibrium / equilibrium / reversible

1 1

(ii) brown colour increases/ intensifies equilibrium shifts to the right / forward reaction favoured / more NO2 forms

1 1

(iii) brown colour decreases/ fades / turns colourless 1 (d) Formula mass (NH4)2SO4 = 28 + 8 + 32 + 64 = 132 1

% nitrogen = 28 x 100/ 132 ½ = 21% ½ If some steps in the working are missing but ans is correct award full marks

2

(e) (i) 3CuO(s) + 2NH3(g) → 3Cu(s) + N2(g) + 3 H2O(l) all symbols correct award 1

balancing correct award 1

2

(ii) NH3 is oxidized OR CuO is reduced ½ because NH3 lost hydrogen / oxidation state of nitrogen increased / nitrogen lost electrons / CuO lost oxygen / O.S. of copper decreased

½

1

(iii) black solid decreases/ pink solid formed / condensation on some parts of apparatus

1

Total 20 marks

  1  

Marking Scheme - May 2011 Paper 2A

Section A

2 a Zn2+ = +2 H = 0

½ ½ 1

b

Loses Oxidised Gain Reduced

½ ½ ½ ½

2

c

Zn → Zn2+ + 2e- 2H+ + 2e- → H2 Accept as correct if the equations are given with the electrons being subtracted instead of added.

1 1

2

d No 1 Total 6 marks

1 a

Different atoms of the same element having the same number of protons (or proton number) but different number of neutrons (or mass number) in their nuclei

If ‘same element’ is omitted or ‘two elements’ given deduct ½ mark.

½ ½ 1

b

atom 79Br ion 81Br -

protons 35 35

neutrons 44 46

electrons 35 36

Award marks for correct values only.

½ x 6 = 3

c

RAM = [(79*51) + (81*49)] / 100 = 80 All the steps must be shown to obtain any marks.

1 1 2

Total 6 marks

  2  

3 a ΔHc, is the amount of heat given out when 1 mole of substance is completely burnt in oxygen (or excess air).

½ ½ 1

b

C3H8 + 5O2 → 3CO2 + 4H2O Balanced equation Correct symbols 3 mol of CO2 = 1 mol C3H8 moles of C3H8 = 4.5 / 3 = 1.5 mol ΔHc for C3H8 = 3300 / 1.5 = - 2200 kJ mol-1 Deduct 1 mark if the answer does not include a negative sign. If not all the steps are shown but some of the steps lead to the correct answer award full marks.

1 ½ ½ ½ ½ 1

4

c

Each correct axis Each correctly labeled energy level

½ ½

2

Total 7 marks

4 a i Allotropes are different forms of the same element in the same state.

½ ½ 1

ii Rhombic Monoclinic

½ ½ 1

b i Oxidizing agent 1

ii Dehydrating agent (No marks for drying agent as answer)

1

iii As an acid 1

c Accept any one of the following: Vulcanization of rubber / agriculture / matches / gunpowder / etc\ Do not accept: contact process /manufacture of sulfates/ fertilizer.

1

Total 6 marks

C3H8 + 5O2    or Energy level of reactants  

CO2 + 4H2O or  Energy level

of products  

Energy  

Progress of reaction  

  3  

5 a

Copper (II) sulfate-5-water is dissolved in water Award marks if dissolution omitted but students indicates use of

solution. Magnesium metal is added to the solution. Any one of the following:

• Pink deposit of copper • Magnesium dissolves • Blue solution gets paler / colorless solution.

Mg + CuSO4→ Cu + MgSO4 All symbols correct Alternative answer Heat / react magnesium with copper (II) oxide.

Do not accept ‘mix’ Any one of the following:

• A violent reaction occurs • Pink copper forms • Black colour of copper(II) oxide disappears • White magnesium oxide forms

Mg + CuO → Cu + MgO All symbols correct

½ ½ 1 1 1 1 1

3

b

• calcium oxide • is added to warm dilute nitric acid • until excess solid remains.

• The solid is filtered off. • The filtrate is added to sodium carbonate solution. • Calcium carbonate precipitate is filtered off.

In the last step the student must indicate formation of ppt or filtration to get ½ mark.

Do not accept CaO with H2SO4.

½ ½ ½

½ ½ ½ 3

Total

6 marks

  4  

6 a

Award ½ mark for each correct charge. Award ½ mark for each correct diagram.

½ x 4 = 2

b Ionic or electrovalent bonding It is the electrostatic attraction between oppositely charged ions.

Do not accept a bond between metal and non-metal.

1 1 2

c Na2O Award ½ mark for MgO.

1 1

d i Covalent bonding 1

ii

Accept any two of the following: • SiO2 has a giant (or macromolecular) covalent structure • Silicon and oxygen atoms are held together by very strong

covalent bonds. • These bonds require very high temperature/energy to break.

½ x 2 = 1

Total 7 marks

7 a

Butanoic acid

1 1

2

b i Esterification 1 1

ii

All formulae correct Equilibrium sign

1 1

2

iii

Any of the following:

• Neutralizes the butanoic acid • Removes the smell of the acid • Makes it possible to smell the fruity ester.

1

Total 6 marks

  5  

8 a The reaction would be to violent / Na too reactive / rxn dangerous 1

b

Only award marks for the drawing and/or labelling of the following:

• Combustion tube / glass tube (drawn and labeled) • Boat containing solid CuO (drawn and labeled) • Heating the CuO • Burning excess hydrogen.

½ ½ ½ ½

2

c i

Any one of the following:

• Does not produce CO2, which is a greenhouse gas • Non-pollutant / clean fuel • Renewable fuel • Saves on fossil fuels

1

ii

Any one of the following:

• High cost of hydrogen. • Hydrogen cannot be liquefied at room temperature. • Dangerous gas (explosive)

1

Total 5 marks

9 a

A = CaCO3 (do not accept ‘calcium cabonate’) A = limestone B = Ca(OH)2 B = slaked lime Do not award marks for lime water.

½ ½ ½ ½

2

b

CaCO3 (s) + H2O (l) + CO2 (g) → Ca(HCO3)2 (aq) Balanced equation and all formulae correct All state symbols correct

1 1

2

c

• Boiling the tap water / Distill (Do not accept heat) • thermally decomposes the Ca(HCO3)2 OR (produces CO2

gas, water and calcium carbonate) • CaCO3 precipitates out of solution • The suspension is filtered to remove the CaCO3 OR water

collected as distillate

½ ½ ½ ½

2

Total 6 marks

  6  

10 a i Oxygen 1

ii Approximately 79 cm3 Accept ans as percentage

1

iii • Oxygen reacts with carbon • forming gaseous CO2

½ ½ 1

b i Nitrogen 1

ii

Any two of the following: • Unreactive / does not react with food • Removes O2 / slows the bacterial growth / slows the decay

of the food / keeps food fresh / food preservation. • Slows the oxidation of food / retains the flavour of the food • Liquid N2 used to fast freeze food.

½ x 2 = 1

Total 5 marks

  7  

Section B

11 a i

A catalyst is a substance that • Alters / increases the rate of reaction but • is still present at the end of the reaction / without being

used up Deduct 1 mark for ‘Does not take part in the reaction’

1 1 2

ii

• During the reaction oxygen is produced / increase in volume.

• A known volume of hydrogen peroxide • is placed in container connected to a gas syringe • a small amount of MnO2 is added.

• The reaction is left for a fixed amount of time • the volume (of oxygen produced) is measured at several

intervals.

Award marks if the sections in bold are mentioned Accept correct if the decrease in mass of hydrogen peroxide is followed (no gas syringe but must include balance)

½ ½ ½ ½ ½ ½

3

iii

Correct x-axis

Correct y-axis (Do not accept ‘products)

Each correctly labelled curve Or a relevant graph showing a decrease in the mass of hydrogen peroxide.

½ ½

1, 1

3

b i The decrease in the concentration of the reactants with time or the increase in the concentration of products with time.

1

ii

• particles move faster (or higher kinetic energy) / more collisions.

• particles collide with more energy • more of the collisions result in a reaction / more successful

collisons (Do not accept ‘makes rxn faster’)

1 1 1

3

c i Decrease 1 ii Increase 1

iii 5 minutes The rate of reaction approximately doubles when the temperature increases by 10 oC

1 1 2

  8  

d i

Any of the following: • The rate of reaction increases in the presence of sunlight/

light. • Light is a form of energy and therefore it increases the rate

of reaction / the energy of the reactants increases. • Reaction is photo-catalysed.

2

ii

The green colour of the chlorine gas disappears as the reaction proceeds.

1

iii Faster F2 more reactive / better oxidizing agent

½ ½

1

Total 20 marks

12 a i A compound that contains only carbon and hydrogen atoms. 1 1

ii • Carbon can catenate / form chains of C atoms • An atom of carbon can form stable (or strong) covalent

bonds with other carbon atoms.

1 1 2

iii Gases (or fuel gas) (Do not accept LPG) Petrol (or gasoline) / naphtha

½ ½ 1

iv

Any two from: • different sized molecules / different RMM / more or less

(carbon) atoms (in molecules) / different structures. Ignore different densities.

• fuels have different boiling points • fuels condense at different temperatures.

1 x 2 = 2

v

Cracking is the process where • large hydrocarbon molecules are broken into smaller

hydrocarbon molecules. • High temperatures • High pressure / a catalyst

C10H22 → C8H18 + C2H4 Accept other correct equations

1 ½ ½ 1

3

b i The greenhouse effect / global warming 1

ii No Crude oil is a non-renewable resource

½ ½ 1

iii

Any two from: • Toxic carbon monoxide gas is given off / formation of

carboxy haemoglobin / does not allow O2 to reach brain • Inefficient use of the fuel / not all the energy of the fuel is

used) • Soot produced / impurities remain

1 x 2 = 2

  9  

c i

C9H18O6 RMM = (12*9)+(1*18)+(16*6) = = 222 If not all the steps are shown but some of the steps lead to the correct answer award full marks.

½ ½ 1 2

ii

3 moles of gases are produced. 3 * 22.4 dm3 = 67.2 dm3

1 ½ ½

2

iii

V1 / T1 = V2 / T2 T2 = 273 + 500 = 773K (award ½ for 273 and ½ for 500) V2 = (67.2 / 273) * 773 = 190 dm3

1 ½,½ ½ ½

3

Total 20 marks

13 a i A = Chlorine B = Hydrogen C = Sodium hydroxide

1 1 1

3

i

2Cl- → Cl2 + 2e- All symbols correct Balancing correct Accept as correct if the equations are given with the electrons being subtracted instead of added.

1 1 2

iii

2H+ + 2e- → H2 All symbols correct Balancing correct Accept as correct if the equations are given with the electrons being subtracted instead of added.

1 1 2

iv

Q = IT Q = 86500 * 3600 = 3.114 x 108 C no of moles of electrons = 3.114 x 108 / 96500 = 3227 moles

1 ½ ½

2

v

2 mol of e- : 1 mol of Cl2 Moles of Cl2 = 3227 / 2 = 1614 moles Mass of Cl2 = (1614 * 71) / 1000 = 114.6 kg Deduct 1 mark if the answer is given in grams.

½ ½ 1 1

3

b i

Any one of the following: • Sterilizing potable water / Manufacture of bleaching

products • Production of plastics (such as PVC) • Extraction of Bromine

1

  10  

ii

Semi-permeable membrane / asbestos or polymer membrane (award ½ mark for ‘membrane’ only or diaphragm) It allows Na+ ions from the brine to pass through Na+ combines with the OH- ions forming NaOH.

1 ½ ½ 2

iii

Manufacture of paper / soaps / detergents / Purification of bauxite/ Production of Aluminium / absorption of acidic gases - industrial Drain cleaning agents – domestic As a strong alkali / neutralization of acids / tests for cations - lab

1 1 1

3

c i Hydrogen chloride 1

ii Acid / detect ammonia 1 Total 20 marks

14 a i A solution of known concentration. 1

ii • A substance which ionizes completely in water • to give OH- ions.

½ ½ 1

iii

C2O4H2.2H2O RMM = (12*2)+(16*4)+(1*2)+(18*2) = = 126 If not all the steps are shown but some of the steps lead to the correct answer award full marks.

1 1 2

iv

moles of C2O4H2 = 1.85 / 126 = 0.0147 mol

If not all the steps are shown but some of the steps lead to the correct answer award full marks.

1 1

2

b i Detect the end-point / stop the titration Accept ‘to indicate complete neutralization’

1

ii No Gradual changes in colour / no sharp end-point

1 1 2

iii Pipette / bulb pipette / graduated pipette Do not award marks if measuring cylinder / teat pipette is given.

1

iv

moles of C2O4H2 in 25 cm3 = 0.0147 / 10 = 0.00147 mol 1 mole of C2O4H2 : 2 moles of NaOH moles of NaOH in 15 cm3 = 0.00147 * 2 = 0.00294 mol conc of NaOH = (0.00294 * 1000) / 15 = 0.196 mol dm-3 If not all the steps are shown but some of the steps lead to the correct answer award full marks. Deduct ½ mark if no suitable units are given.

1 1 1 1 1 5

  11  

c i

• CO2 is absorbed by the solution. (award the ½ mark if CO2 only is mentioned)

• Reacts with NaOH to give the carbonate.

Neutralisation reaction

½ ½ 1

2

ii

2NaOH (aq) + CO2 (g) → Na2CO3 (aq) + H2O (l) Balanced equation All state symbols correct

1 1 2

iii Exothermic 1 Total 20 marks

  1  

Marking Scheme – May 2011 Paper 2B SECTION A 1 a i 5 neutrons 1 ii 6 neutrons 1 b i 6 electrons 1 ii No charge, neutral 1 c (10 X 1) + (11 X 4)

1 + 4 = 10.8

1

1 Total 6 marks

2 a i 2H+ + CO3

2- → H2O + CO2 All formulae correct

All charges correct

1 1

ii Zn + 2H+ → Zn2+ + H2

All formulae correct All charges correct

1 1

b i Hydrogen / H+ / Hydrogen ions Do not Accept H2 1 ii Reduction in oxidation state of hydrogen, Gain of electrons by the hydrogen

ions 1

Total 6 marks

3 a 1 mole of C3H8 = (12 X 4 + 1 X 8) = 44 g ? = 66 g 66/44 = 1.5 moles

½ ½ ½ ½

b 1.5 moles = 3330 KJ 1 mole = ? 3330 = 2220 KJ mol-1 1.5

½ ½

c The quantity of heat released when 1 mole of substance is completely burned in excess of air

½ ½

d Exothermic 1 Total 5 marks

4 a i When an element is present in 2 or more different forms

without a change of state ½ ½

ii Rhombic Monoclinic (needle shape)

Accept plastic sulfur

1 1

b i Accept any three of the following: Oxidizing agent Dehydrating agent Drying agent Acid. Accept to make sulfates.

1 x 3

c One out of: agriculture / gunpowder / matches / vulcanization of rubber

1

Total 7 marks

  2  

5 a i Sodium 1 ii Silver 1 b i Forms very strong bonds with other elements

that are not easily broken or Forms stable compounds that are difficult to reduce.

½ ½

ii Rubidium iii Zn + 2AgNO3 → Zn(NO3 )2 + 2Ag Correct Equation

Correct Balancing

1 1

Total 6 marks

6 a

Correct Structure Correct Bonding

½,½ 1

b i Red litmus – no change Blue litmus to red

½ ½

ii Inverted funnel + labelling (Beaker / test-tube) with water + labelling Inverted funnel touching the water

½,½ ½,½

1 Total 6 marks

7 a Ethanoic acid 1 b Effervescence / gas evolved (or given off)

1

c CH3COOH + CH3OH CH3COO CH3 + H2O Correct formulae

Accept molecular formulae Equilibrium sign

1 1

d Conc. H2SO4 OR Dry HCl 1 e Sweet / fruity smell/characteristic smell of ester 1

Total 6 marks

8 a Copper is less reactive than hydrogen or Copper is below hydrogen in the reactivity series or Copper cannot displace hydrogen from an acid

1

b Two of: fume cupboard Safety glasses / gloves / lab coat (Accept only one safety wear) No flames in proximity of the gas Make small volumes

1 1

c i One of: It does not cause any pollution A renewable source of energy Saves on fossil fuels Accept: does not produce greenhouse gases

1

ii One of:Too costly to produce Explosive (Too dangerous) Cannot be liquified at rtp

1

Total 5 marks

  3  

9 a Substance A = calcium oxide / quicklime

Substance B = calcium hydroxide / slaked lime / lime water

1 1

b i CaCO3 + H2O + CO2 → Ca(HCO3)2 2 ii Advantage = provides calcium important for bones and teeth

Disadvantage = Furring / wastage of soap / blocking pipes / scaling 1 1

iii Sodium carbonate OR washing soda OR Na2CO3.10H2O / Na2CO3 1 Total 7 marks

10 a i Oxygen / O2 1 ii Approximately 79 cm3 1 iii Ozone 1 b i Nitrogen 1 ii Any two of the following:

• Unreactive / does not react with food • Removes O2 / slows the bacterial growth / slows the decay of the food

/ keeps food fresh / food preservation. • Slows the oxidation of food / retains the flavour of the food • Liquid N2 used to fast freeze food.

Do not accept ‘not to crush food’

1 1

Total 6 marks

  4  

SECTION B 11 a i A substance that

Alters / increases the rate of the reaction Is still present at the end of the reaction Deduct 1 mark for ‘Does not take part in the reaction’

1 1

ii

Axis

Correct position of graphs and labelling

1,1 1 ½, 1 ½

iii SO3 – Vanadium pentoxide / Vanadium(V) oxide NH3 – Iron

1 1

b i Surface area 1 ii Heat / increase in temperature

Increase concentration Accept catalyst

1 1

iii

Axis

Correct position of graphs – shape

1,1 1,1

c i Any of the following: • The rate of reaction increases in the presence of sunlight /light. • Light is a form of energy and therefore it increases the rate of reaction

/ the energy of the reactants increases. • Reaction is photo-catalysed.

2

ii Yellow green colour fades Do not accept white fumes of HCl / explosion

1

iii Faster 1 Total 20 marks

  5  

12 a i A = Concentrated NaCl / brine B = Hydrogen Substance C = Sodium hydroxide

1 1 1

ii 2Cl- - 2e → Cl2 Correct equation Correct Balancing & Charges

1 1

iii 2H+ + 2e → H2 Correct Equation Correct Balancing & Charges

1 1

b i 86500 x 60 x 60 = 311400000C

1 1

ii 1 mole = 96500C ? = 311400000C 311400000/96500 =3227 mol

1 1

iii 2 moles of e → 1 mole of Cl2 3226.94moles → ? moles 3226.94/2 = 1613.5 moles of Cl2

½ ½

iv 1 mole of Cl2 = 35.5 x 2 = 71g 1613.47 moles = 1613.47 x 71 114556 g OR 114.6 kg

1

1 c i One of : Hydrogen chloride/Hydrochloric acid

Manufacture of plastics PVC Manufacture of bleaching products/Bleaching Agent Sterilizing of water

Extraction of Bromine

1

ii Industrial use: Manufacture of paper OR Manufacture of soap OR Purification of bauxite/Production of Aluminium Domestic use: Drain cleaner/unblocker Laboratory use: Neutralization of acids / alkali

1

1 1

d i Hydrogen chloride (No marks given for giving Hydrochloric acid as answer)

1

ii Production of hydrochloric acid / acid 1 Total 20 marks

  6  

13 a Fractional Distillation 1 b i A=Gas fuel / gas

B=Petrol / gasoline / naphtha C=Fuel Oil / oil D=Asphalt / paraffin wax / tar / lubricating oil

1 1 1 1

ii

No marks awarded for structures with carbon and/or hydrogen having the incorrect number of bonds Half a mark is awarded if basic chain is correct but hydrogen atoms not written down

1, 1

1, 1

iii Any one of: Kerosene = aircraft fuel Paraffin oil = heating oil

1,1

iv CH4 + 2O2 → CO2 + 2 H2O For using CH4

Correct equation and balancing

1 1

c Catalytic cracking OR Cracking • High temperatures • High pressure / a catalyst

1 1 1

d ii No Crude oil is a non-renewable resource or similar

½ ½

ii Carbon monoxide 1 iii Any two form

• Toxic carbon monoxide gas is given off / formation of carboxy haemoglobin / does not allow O2 to reach brain

• Inefficient use of the fuel / not all the energy of the fuel is used • Soot produced / impurities remain

1 1

Total 20 marks

  7  

14 a i RMM of Na2CO3 = 106 1 mole = 106g 0.5 moles = ? 106 x 0.5 = 53g

½ ½ ½ ½

ii Any three of the following: Balance = to weigh the solid Volumetric flask = to make a solution of 1 dm3 Watch glass/petri dish/weighing boat = to weigh 53g of solid Funnel = to transfer solid to beaker Wash bottle = to wash apparatus that contained solid Beaker / flask = to carry out the dissolving Stirrer = to dissolve the solid

1,1 1,1 1,1

iii Two out of; all watch glass/petri dish and funnel are washed properly all washings go into the beaker when the solution is made to the mark the reading is taken at eye-level precise weighing

1,1

b i 1000 cm3 = 0.5 moles 25 cm3 = ? 25 x 0.5 1000 = 0.0125 moles

1

1

ii 1 mole of Na2CO3 reacts with 2 moles of HCl 0.0125 moles reacts with 2 x 0.0125 moles 0.025 moles

½ ½

iii 34.5 cm3 = 0.025 moles 1000 cm3 = ? 1000 x 0.025 34.5 = 0.72 mol dm-3

1

1

iv To determine the end point / stop the titration 1 v No

Gradual changes in colour / no sharp end-point 1 1

vi The volumetric pipette is used to measure the 25 cm3 of Na2CO3 and transfer it into the conical flask The burette is used to measure the volume of acid that is required to neutralize the Na2CO3

½ ½ ½ ½

Total 20 marks