10 IGCSE Coordinated Science Mock Examination 2014 Paper 6 Marking Key

Question number

Answer Notes Marks

Q1. (i) A / clearly identified; smallest scale divisions / measures to 0.2 (mL);

ALLOW the one measuring in ml (identifies A in picture)

MUST have chosen A DO NOT ALLOW it measures in ml

1 1 (ii) any ONE suitable e.g.

incorrect scale / calibration;

misreading scale / parallax /not at eye level;

meniscus makes it difficult to read;

might not be level / flat;

reading may be between divisions;

DO NOT ALLOW hard to measure

1

Total = 3

Q2. (a) (i) It is a source of heat/ to provide heat/ OWTTE (must mention heat) 1 (a) (ii) Volume of cold water used (30 cm3)/distance of boiling tube from infra red lamp/ initial temperature of water/ amount of surface area exposed to heat (same boiling tube) Do NOT accept temperature was read every 5 mins or switching on the lamp; Cannot get mark for surface area by simply stating same boiling tube

1

(a) (iii) More precise that thermometer (can measure to 1d.p.)/avoids human errors such as parallax error, failure to read temp at correct time,etc./shows trend as data id being gathered/ avoids having to plot data to see trend/

Do NOT accept more accurate without clear and valid argument; Do not accept avoids human error without clarification. 1

(b) (i) To establish rate of heating absorbance without insulation/ to act as a control that other parts of experiment (with different types of insulation) can be compared to/

Reject: to act as a comparison (if no further information given) 1

(b) (ii) Plastic and aluminium foil 1 Total = 5 3. (a) (i) tube contents entered in table correctly.

tube 1: (protein, pepsin, water) *done already tube 2: protein, pepsin, hydrochloric acid tube 3: protein, water tube 4: starch, amylase, water tube 5: starch, amylase, hydrochloric acid tube 6: starch, water

Must have correct contents for tubes 2-6; (do NOT penalise the omission of water)

1

(a) (ii) observations recorded clearly: cloudy in tubes 1 and 3 (1) clear in tube 2 (1) Ignore any other comments 2

(a) (iii) observations recorded clearly: brown iodine in tube 4 (1); blue/black in tubes 5 and 6 (1) 2

(b) (i) pepsin 1 (b) (ii) enzyme prevented from working by the acid/has an optimum pH/is denatured by the acid / works better in neutral solution Reject: to act as a comparison (if no further information given)

1

(b) (iii) to act as a control/check that no breakdown occurs unless enzyme is present 1 (c) add biuret reagent (or copper sulphate + alkali) (1); turns lilac / purple /mauve (2) 2

Total = 10 4. (a) same mass of soil/ same volume of water ; 1 (b) (from) blue ; (to) red ; 2 (c)(i) 4.4 ; 4.9 ; 5.2 ; 3 (c)(ii) 5.6, 5.1, 4.8 (all three,ecf) ; 1 (c)(ii) (5.6 + 5.1 + 4.8 = 15.5, 15.5/3 =) 5.17 OR 5.2 ; Must have some working for 2 marks 2 (d) 2 0.013 10 / 5.2 = 0.05 (mol/ dm3) (ecf) ; Ignore more than 2 d.p.s 1 Total = 10 marks 5. (a)(i) 0.5 (dm3) Tolerance of + 0.02 1 (a)(ii) 12 No tolerance; award 1 only if correct answer not supported with working.

2 (a)(iii) 6 (dm3) Award 1 only if correct answer not supported with working 2 (b)(i) larger volume inhaled ; rate of breathing slowing down ; volume of each breath falling ;

Maximum (2) 2 (b)(ii) 1.6 (dm3) No tolerance 1 (b)(iii) more oxygen needed (during exercise) ; more CO2 needed to be removed (during exercise) ; oxygen debt ;

Maximum (2) 2 (c) too much carbon dioxide present ; (1) not enough oxygen present (1)

2 Total = 12 marks 6. (a)(i) 21 mm (+/- 1 mm), 2.1 cm3 (+/- 1 cm) (1); volume correctly calculated - 9.3 cm3 (accepted range: 8 cm3 10.6) or e.c.f (1)

BOTH correct values needed for 1st mark; Second d.p.not needed in volume 2

(a)(ii) 25.1 g (+/- 0.05 g) (1) density: 25.1/9.3 = 2.7 g/cm3 (e.c.f.) (1) 2

(b)(i) 110 cm3, 10 cm3

Both correct values needed for mark, no tolerance 1 (b)(ii) 20 cm, 40 cm Reject answers stated the wrong way round; both correct values needed for the mark. 1

(b)(iii) 50 x 20 = mass x 40,(e.c.f.) mass = 25 g (e.c.f.) (1) 1 (b)(iv) 25/10 = 2.5 g/cm3,(e.c.f.) 1 (c) EITHER method 2 is more accurate because the cube in method 1 is not accurately formed (1) so measurement of the side is inaccurate (1) OR the scale of the measuring cylinder used in method 2 is not fine enough (1) so accuracy of measuring volume is low (1) therefore method 1 is more accurate.

Note that the 2 marks can be awarded if an inaccuracy is referred to; if the candidate claims that e.g. finding the volume by displacement is more accurate then award 1 mark maximum. No mark for an answer without a reason!

2

Total = 10 marks 7. (a)(i) use of tongs; lab coat; not looking directly at flame; or blue glass; mentioned Do not accept safety goggles 1 (a)(ii) magnesium oxide is insoluble in water 1 (a)(iii) the mixture is (slightly) alkaline OWTTE 1 (b)(i) magnesium oxide dissolves/reacts in sulfuric acid or is a base oxide (1 only); forms a salt or takes part in neutralization (2) 2

(b)(ii) to neutralise all the acid OWTTE 1 (b)(iii) diagram shows filter funnel and filter paper(1); and passage of mixture through it. (1) Label showing filtrate in vessel below funnel give second mark 2 (c)(i) to concentrate the solution/to evaporate OWTTE 1

some water/controlled heating (c)(ii) the solution is saturated/the magnesium sulphate cannot be held in solution OWTTE 1

Total = 10 marks