GCSE MARKING SCHEME - Ysgol John · PDF fileINTRODUCTION The marking schemes which follow were those used by WJEC for the Summer 2010 examination in GCSE SCIENCE -

GCSE MARKING SCHEME

SCIENCE - CHEMISTRY SUMMER 2010

INTRODUCTION The marking schemes which follow were those used by WJEC for the Summer 2010 examination in GCSE SCIENCE - CHEMISTRY. They were finalised after detailed discussion at examiners' conferences by all the examiners involved in the assessment. The conferences were held shortly after the papers were taken so that reference could be made to the full range of candidates' responses, with photocopied scripts forming the basis of discussion. The aim of the conferences was to ensure that the marking schemes were interpreted and applied in the same way by all examiners. It is hoped that this information will be of assistance to centres but it is recognised at the same time that, without the benefit of participation in the examiners' conferences, teachers may have different views on certain matters of detail or interpretation. WJEC regrets that it cannot enter into any discussion or correspondence about these marking schemes. PAGE Chemistry - C1 1 Chemistry - C2 19 Chemistry - C3 34

1

GCSE Mark Scheme – Chemistry 1 Foundation only questions – Summer 2010 Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not accept 1

(i)

3 yes – B (1) no – C (1) metal – D (1)

(ii) 1 conducts heat / malleable / ductile

high boiling point conducts sonorous high density

2

Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not accept 2

(i) 1 plates

tectonic plates

(ii) 1 slowly

(iii) 2 earthquakes (1) volcanoes (1)

3


(i) 1 iron / oxygen Fe / O2 iron powder

FE / O

(ii) 1 iron oxide FeO / Fe2O3 oxide

(iii) 1 high temperature

burns / very hot / hot – needs qualifying

(iv) 2 identifying the two substances – lithium carbonate and copper chloride (1) identify the correct positions for the substances – lithium carbonate at the top and copper chloride at the bottom of the sparkler (1)

4


(i) 2 hydrogen (1)

oxygen (1)

H2 / H O2 / O

(ii) 1 NH4NO3 − must be correct ammonium nitrate

(iii) 1 D

5


(i) 1 75 nm

(ii) 2 to coat the inner surface of refrigerators (1) in sterilizing sprays to clean operating theatres in hospitals (1)

6

Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not accept 6 (i) 1 345 / 346

(ii) I 1 increase

II 1 increases

III 1 global warming

greenhouse effect climate change

7


(i) 2 H3PO4 (2) [ HPO (1) / 3 4 (1)]

(ii) I 1 MgO Mg2+O2-

II 1 CaBr2 Ca2+Br−2 / Ca2+(Br−)2

8


(i) 3 all points plotted correctly (2) any five points plotted correctly (1)

curve of best fit through all points (1) consequential curve

(ii) 1 38 ± 1.0 consequential

(iii) 1 0-1 minute

(iv)

2 40 (1) volume of gas depends on the mass of magnesium used / acid in excess in both experiments (1)

9

GCSE Mark Scheme – Chemistry 1 Common questions – Summer 2010 Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not accept 9 1 (i) 2 B and F (1)

both have one electron in their outer shell / same number of electrons in their outer shell (1)

sodium and potassium / Na and K / 2, 8, 1 and 2, 8, 8, 1

'finishes in 1' both in Group 1

(ii) 2 A (1)

oxygen / O / O2 2, 6

two electron shells (1)

two orbits has two numbers

(iii) I 1 B

2, 8, 1 Na

II 1 fluorine / bromine / iodine / astatine

F / Br / I / At F2 / Br2 / I2 / At2

chlorine / Cl / Cl2

10

Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not accept 10 2

(i) 2 A (1)

biggest increase in temperature (1)

temperature increases 21−27

highest final temperature

(ii) 2 bubbles / colour change / precipitate formation – any two for (1) each

fizzing / brown solid formed

colour new substances / products formed

substance disappears

11


(i) I 1 2Na + Cl2 2NaCl i.e. fourth equation (1)

II 1 yellow orange

(ii) I 2 potassium iodide + chlorine (1) potassium chloride + iodine (1)

KI + Cl2 (1) KCl + I2 (1) (ignore balancing)

KI solution / CI2 gas potassium iodide solution / chlorine gas

II 1 chlorine is toxic

poisonous iodine is toxic

harmful / dangerous

12

GCSE Mark Scheme – Chemistry 1 Higher only questions – Summer 2010

Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not accept

4

(i) I 1 magma molten rock lava

II 1 igneous

(ii) 1

earthquakes

mountain ranges ocean trenches oceanic rifts

subduction / tsunami

13


5 (i) 2 B (1) conducts electricity (1) density – needs qualifying

e.g. less dense than water

mp 98 / density 0.97

(ii) 2 A (1) boiling point lower than

room temperature or 20oC (1)

density – needs qualifying e.g. very low gas at room temperature

gas

14


6 (i) 1 any number between 1 and 100 / range 1–100

any appropriate range

(ii) 2 sterilising sprays (to clean operating theatres in hospital) / refrigerator surfaces / wound dressing / deodorant socks / hospital clothing – any two for (1) each

15

Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not

accept 7

(i) I 1 increase

II 1 369 – 326 = 43 ± 0.5 per reading therefore ± 1.0 for change (range 42−44)

(ii) 2

increased burning of (fossil) fuels (or named fuel) (1) deforestation (1)

more cars more power stations

(iii) I 1 increase in winter / decrease in summer

II 1 more fuel burnt in winter / fewer plants in winter / less photosynthesis in winter / seasonal uptake by plants less in winter – any one

less sunshine in winter

16


8

(i) I 2 curve to the right of graph A (1) aiming towards 30 cm3 / levelling off at 30 cm3 (1)

II 2 curve to the left of graph A (1) levelling off at 60 cm3 before 30 s (1)

(ii) 2

more energy / move faster (1)

greater chance of a collision / more (effective) collisions in a unit /set time (1)

more collisions / successful collisions

17


9

(i) I 2 4(413) + 2(498) (1)

2648 (1)

answer only (2)

II 2 2(805) + 4(464) (1)

3466 (1)

answer only (2)

(ii) 1

energy needed to break the bonds is less than the energy given out in making bonds / −818 / overall energy change has negative value – any one

more energy given out than taken in

818 / heat given out

18


10 (i) I 1 potassium

K

II 3 2K + 2H2O 2KOH + H2 2M + 2H2O 2MOH + H2 reactants (1) products (1) balancing if both reactants and

products are correct (1)

consequential marking for Group 1 element

(ii) I 1

Na2CO3 (1) Na+2CO3

2− / (Na+)2CO32−

II 3

add hydrochloric acid (to both) (1) sodium carbonate bubbles/fizzes (1) no observation seen with sodium chloride (1) or add (pH) indicator (to both) (1) sodium carbonate pH > 7 / alkaline (1) sodium chloride pH = 7 / neutral (1)

silver nitrate (1) white ppt with NaCl (1) -2 max

19

GCSE Mark Scheme – Chemistry 2 Foundation only questions – Summer 2010

Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not accept 1 (a)

(i) 1 12%

(ii) 1 toilet (flushing) flushing 30%

(iii) 1 20% (2) 30 + 17 + 14 + 12 + 7 = 80 (1) 100 – 80 = 5% (1)

(b)

(i) 1 filtration

(ii) 1 chlorination

20


(i) 1 12

(ii) 1 24

(iii) 1 2,8,2

(b)

(i) 1 nucleus

(ii) 2 electrons (1) orbits / shells (1)

(iii) 1 protons

21


(i) I 1 sodium chloride / copper sulphate

II 1 carbon dioxide / water

(ii) I 1 transfer of electrons (from a metal atom to a non metal atom)

II 1 sharing (pairs of) electrons

(iii) 1 they have low melting and boiling points

(iv) 2 conductivity (1) melting point (1)

boiling point solubility

electricity

22


(i) 2 reactants : nitrogen + hydrogen (1) product : ammonia (1)

(ii) 1 reaction can go both ways can go back can be reversed

(b)

(i) 1 ammonium sulphate (NH4)2SO4

(ii) 1 neutralisation exothermic chemical

(iii) 1 nitric acid HNO3

(c) 2 advantages: increase crop yield / healthier crops / improve soil quality / reduces land needed (any 1)

cheap

disadvantage: pollute water supplies / eutrophication / blue baby syndrome / stomach cancer (any 1)

accept description of stages in eutrophication e.g. overgrowth of algae, oxygen depletion leading to killing fish

pollutes water / kills fish

23


(i) 1 can regain shape (when bent) go back to original shape

superelastic keep their shape can’t be bent

(ii) I 1 photochromic pigment

II 1 change colour in sunlight / light in uv light

6

(i) 1 chromium Cr carbon

(ii) 1 contains more carbon mild steel contains less carbon

contains carbon

(iii) 1 mild (steel)

(iv)

1 doesn't corrode doesn’t rust hardwearing hard, tough

24

GCSE Mark Scheme – Chemistry 2 Common questions – Summer 2010

Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not accept 7 1 (a)

I 1 6% (range 5.5−6.0%)

II 1 40% (no tolerance)

(b)

(i) 1 build up of limescale

furring up boiler scale

hard water scale

scum

(ii) 1 Area B has harder water more limescale has built up in area B less Ca2+ / Mg2+ in area A

A is soft water

25


(i) 1 magnesium, zinc, iron, copper (all need to be correct)

Mg, Zn, Fe, Cu

(ii) I 2 reactants : magnesium + copper sulphate (1) products : magnesium sulphate + copper (1)

Mg + CuSO4 (1) MgSO4 + Cu (1) ignore state symbols / balancing

powder / solution in word equation

II 1 magnesium is more reactive than copper

magnesium displaces copper

(iii) I 1 C more reactive than / above Fe but less reactive than / below Al

Al > C > Fe (but must show clearly

carbon is between iron and aluminium (in reactivity series)

II 1 electrolysis

reaction with a more reactive metal or given example

26

Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not accept 9 3 (a)

(i) 1 (addition) polymerisation

(ii) 2 ethene has double bond / polythene has no double bond; ethene is unsaturated / polyethene is saturated (1)

only 2 carbon atoms in ethene / many carbon atoms in polythene;

only 4 hydrogen atoms in ethene / many hydrogen atoms in polythene;

ethene is a short chain / polythene is long chain;

(any marking points relating to chain length for 1 mark )

shorter / longer chain

11 C atoms / 22 H atoms in polythene

(iii) 2 28 (2) If incorrect then 1 mark for: (4 x 1) + ( 2 x 12)

27

GCSE Mark Scheme – Chemistry 2 Higher only questions – Summer 2010


3 (b)

(i) 2 thermosets have strong bonds / links between chains / thermoplastics do not have strong bonds between chains / molecules (1) In thermosets, chains cannot slide over each other / chains can slide over one another in thermoplastics (1) response must give / imply comparison

clearly labelled diagrams

tightly packed Reference to layers

(ii) 1 saucepan handles / electrical sockets / light bulb holders / hairdryer casing

TV casing microwave containers

28


4

3 named example (1)

change taking place (1)

cause of change (1)

thermochromic paint

changes colour heat

general definitions or answers that do not give a named example

photochromic paint

changes colour light

shape memory / smart alloy

regains original shape

heat Nitinol

shape memory / smart polymer

regains original shape

heat

polymer gel (hydrogel)

swells or shrinks

water / heat / pH

Nitinol contracts electric current

29


5

(i) 2 6 (1) 66Sc (1) 21

(ii) 1 nucleus

(iii) 1 mass of 1 unit and 0 charge (both needed for mark)

+1 for mass neutral / none for charge

30


6

(i) 3 diagrammatic representation showing clearly Ca losing 2 outer e- (1) two CI atoms, each gaining 1 e- (1) Ca2+ and Cl- (both needed) (1) there must be no ambiguity e.g. electrons cannot be on atoms and ions at same time

(ii) 2 shared pair of electrons between H and Cl (1) full octet around Cl (1)

(iii) 2 strong bonds (between ions) in calcium chloride (1) weak bonds between molecules in hydrogen chloride (1)

ionic bonds are strong weak bonds in hydrogen chloride

reference to atoms or molecules for CaCl2, atoms or ions for HCI

31


7 (a)

(i) 3 reactants : H2 + N2 (1) product : NH3 (1) balancing : 3 , 1, 2 (1) ( both products and reactants must be correct before this can be awarded)

(ii) 1 reversible reaction / reaction can go in both directions

reaction can go back / can be reversed

(b)

(i) 1 curve steeper than 350°C levelling out above 350°C curve

(ii) 1 350°C and 360 atm (both needed) (no tolerance)

(iii) 1 greater yield of ammonia (at higher pressure)

increases / more

(c)

2 162 / 180 x 100 (1) = 90% (1) correct answer (2)

32


8

(i) I

1

liquid / molten

in solution

II 1 ions need to be free to move

electrons free to move

(ii) 1 3e- 3 electrons

(iii) 2 2 oxide ions lose 2e-s each / 4e-s(1) combine to form oxygen molecule (1)

2O2- O2 + 4e-(2) 2O2- - 4e- O2 (2)

reference to attraction

33


9 (i) 3 Mass / Ar :72/12 = 6 ; 16 / 1 = 16 (1) ratio : 6 : 16 / 3:8 (1) formula = C3H8 (1) correct formula without workings = 1 only

(ii) 1

34

Chemistry 3 Foundation only questions June 2010

Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not accept 1 (i)

1 heat

(ii) 3 Fire breaks: removes the fuel / reduces the amount of fuel Foam: removes air / oxygen Water: removes heat ....reference to both 'removing / reducing' and 'the factor' needed

35


(i) 1 sulphuric H2SO4

(ii) 2 • equal volume of acids / 50 cm3 of each acid/ 50 cm3 of sulphuric and 50 cm3 ethanoic acid • equal volumes of alkali / 50 cm3 of alkali / 50 cm3 sodium hydroxide solution • equal time / 1 minute ................. any two

amount ≡ volume same volume of 'solutions' (1)

36


(i) 1 corn / sugar cane / rapeseed ..... any two for (1)

sugar

(ii) 1 petrol

(iii) 1 carbon neutral ..... both words needed

(iv) 1 less food (for developing countries) / increase the price of food ...... any one for (1)

(v) 1 reduce habitats (for animals) / reduce habitats (for plants) ..... any one for (1)

less ≡ reduce

37


(i) I 1 ethane ref. to structural/

molecular formula

II 1

ref. to name / molecular formula

III 1 C2H4

ref. to name/ structural formula

(ii) I 1 ethane C2H6

II 1 ethanol

C2H5OH

38


(i) I 1 air oxygen

II 2 sulphur dioxide + oxygen (1) sulphur trioxide (1)

air

III 1 vanadium oxide / vanadium(V) oxide

IV 1 exothermic

(ii) I 1 detergents

II 1 9

(iii) I 1 volume of 'material' in beaker increased e.g.

reference to steam / bubbles

labelling 'sugar'

II 1 oxygen and hydrogen ..... either order

'O' and 'H' O2 , H2

39


(i) 2 Flame test: (brick) red flame Add dilute hydrochloric acid: bubbles (which can be shown to be carbon dioxide)

red fizzing

gas formed / carbon dioxide

(ii) 2 Flame test: lilac flame Add dilute HNO3 followed by AgNO3: white precipitate

(iii) 1 Test: Add sodium hydroxide solution Result: blue precipitate ...... both for (1) mark

(b)

1 limewater turns milky

40

Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not

accept 7 (i) 1 heat roast /

high temperature

warm / raise temperature / thermal decomposition

burn

(ii) 2 calcium carbonate (1) calcium oxide + carbon dioxide (1)

limestone quicklime

41

Chemistry 3 Common questions June 2010 Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not accept 8 1 (a)

(i) 2 glucose (1)

ethanol + carbon dioxide (1)

'yeast' written on the arrow reference to formulae

glucose solution

(ii) 1 fermentation anaerobic respiration brewing

(b)

(i) 1 ( ethanol and water have) different boiling points / ethanol has a lower b.p. than water / solution ethanol boils at 78oC and water boils at 100oC / it has a lower b.p.

it boils first 'it' ≡ glucose b.p. for ethanol 79oC / 80oC

ref. to 'glucose solution' / boils quicker/ boils

(ii) 3 Process: distillation (1) Changes in state: Flask: boiling / boil (1) Apparatus A : condensing / condensation (1)

evaporation

liquid to gas/ vapour (in flask) gas/vapour to liquid (in condenser)

boiling fractional distillation

42


(i) 1 25 ... no tolerance

(ii) 2 Range : 0 - 55 (1) Peak: at 30 (1) ... accept any height of peak

(iii) 1 any value of -5oC or below or any value of 55oC or above .... either value (1) i.e. ≤ -5 or ≥ 55

43


(i) I 1 A

II 1 E

(ii) 1 (graphite) insoluble in water / (graphite) insoluble in most solvents / ink is soluble in water / ink might be soluble in water / ink might be soluble in most solvents

(graphite) insoluble in all solvents

not affected by water doesn't run in water

(iii) 1 add (chromatogram) to water

mix the three colours together

44

Chemistry 3 Higher only questions June 2010 Question Number FT HT Sub-section Mark Answer Accept Neutral answer Do not accept

4 (a)

(i) I 1 (thermal) decomposition

II 1 heat roast / high temperature

warm / raise temperature reference to actual numerical values

(ii) I 1 carbon dioxide CO2

II 1 water H2O

(iii) 3 reactants: CaO + H2O (1) product; Ca(OH)2 (1) balancing: 1:1:1 (1) product must correct before balancing mark awarded

(b) 1 iron steel

(c) 2 dust (from lorries and blasting) (quarries) spoils landscape noise (from blasting and traffic) (quarries) destroy (natural animal) habitats

destroys landscape 'named animal' e.g. destroys bird habitats

ref. to pollution ref. to 'environment'

45


5 (a)

(i) 1 B and C .... either order C4H10 & C3H8

(ii) 1 A

C3H6

(b) (i) 2 (1) (1) 'H' 's must be present

(ii) 1 same molecular formula , different structural formulae (1) ..... both statements needed for (1) mark

(c) (i) I 1 hydrogen

H2 H

II 1 ethane

C2H6

(ii) 1

46


6

(i) 1 air oxygen

(ii) 3 All five points plotted correctly (2) Any four points plotted correctly (1) .... tolerance +/- 1 'small ' square Curve of best fit (1) ...between 400 and the range 600-620

(iii) I 1 higher the temperature , smaller the yield

II 1 400 to 515 .... tolerance on 515 only of +/- 5

(iv) 3 Reactants: SO2 + O2 (1) Products: SO3 (1) Balancing: 2 : 1 :2 (1) product must be correct before balancing mark awarded

47


7

(i) 1 burette biuret

(ii) 1 identify 'end point' / to know when all the alkali has been neutralised / to know when all the sodium hydroxide has been neutralised / when complete / exact neutralisation has occurred

to know when all the alkali has been cancelled out / to know when all the sodium hydroxide has been cancelled out / to know when all the alkali has been used up / the alkali is now pH 7

(iii) 3 'mv' ='mv' method m × 25 = 20 × 0.25 (1) substitution & ratio m = 20 × 0.25 (1) 25 re-arranging formula m = 0.2 (1) If no workings award (3) marks for the correct answer.

moles = conc. × volume/1000 method moles = 0.25 × 20/1000 = 0.005 (1) substitution 0.05 : 0.05 (1) ratio conc. = 1000/25 × 0.005 = 0.2 (1) substitution & answer

48


8 3 Compound A sodium sulphate (1) Compound B potassium bromide (1) Compound C ammonium carbonate (1)

Na2SO4

KBr (NH4)2 CO3

...formulae must be correct to gain marks

GCSE CHEMISTRY MS - Summer 2010 / JF

WJEC 245 Western Avenue Cardiff CF5 2YX Tel No 029 2026 5000 Fax 029 2057 5994 E-mail: [email protected] website: www.wjec.co.uk

Documents

GCSE MARKING SCHEME - Ysgol John · PDF fileINTRODUCTION The marking schemes which follow were those used by WJEC for the Summer 2010 examination in GCSE SCIENCE -