Mark schemes (a) s 1 1 l Answers must be in the correct order. 1 (b) A gas was lost from the flask 1 (c) Level 3 (5–6 marks): A coherent method is described with relevant detail, and in correct sequence which demonstrates a broad understanding of the relevant scientific techniques and procedures. The steps in the method are logically ordered. The method would lead to the production of valid results. Level 2 (3–4 marks): The bulk of the method is described with mostly relevant detail, which demonstrates a reasonable understanding of the relevant scientific techniques and procedures. The method may not be in a completely logical sequence and may be missing some detail. Level 1 (1–2 marks): Simple statements are made which demonstrate some understanding of some of the relevant scientific techniques and procedures. The response may lack a logical structure and would not lead to the production of valid results. 0 marks: No relevant content. Indicative content • sulfuric acid in beaker (or similar) • add copper carbonate one spatula at a time • until copper carbonate is in excess or until no more effervescence occurs * • filter using filter paper and funnel • filter excess copper carbonate • pour solution into evaporating basin / dish • heat using Bunsen burner • leave to crystallise / leave for water to evaporate / boil off water • decant solution • pat dry (using filter paper) • wear safety spectacles / goggles *Students. may choose to use a named indicator until it turns a neutral colour, record the number of spatulas of copper carbonate added then repeat without the indicator. 6 (d) Total mass of reactants = 221.5 1 Page 32 of 43 www.examqa.com
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Mark schemes
(a) s11
l
Answers must be in the correct order.1
(b) A gas was lost from the flask1
(c) Level 3 (5–6 marks):A coherent method is described with relevant detail, and in correct sequence whichdemonstrates a broad understanding of the relevant scientific techniques and procedures.The steps in the method are logically ordered. The method would lead to the production ofvalid results.
Level 2 (3–4 marks):The bulk of the method is described with mostly relevant detail, which demonstrates areasonable understanding of the relevant scientific techniques and procedures. Themethod may not be in a completely logical sequence and may be missing some detail.
Level 1 (1–2 marks):Simple statements are made which demonstrate some understanding of some of therelevant scientific techniques and procedures. The response may lack a logical structureand would not lead to the production of valid results.
0 marks:No relevant content.
Indicative content• sulfuric acid in beaker (or similar)• add copper carbonate one spatula at a time• until copper carbonate is in excess or until no more effervescence occurs *• filter using filter paper and funnel• filter excess copper carbonate• pour solution into evaporating basin / dish• heat using Bunsen burner• leave to crystallise / leave for water to evaporate / boil off water• decant solution• pat dry (using filter paper)• wear safety spectacles / goggles
*Students. may choose to use a named indicator until it turns a neutral colour, record thenumber of spatulas of copper carbonate added then repeat without the indicator.
6
(d) Total mass of reactants = 221.51
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159.5
221.5
allow ecf from step 11
72.0 (%)1
allow 72.0 with no working shown for 3 marks
(e) any one from:
• Important for sustainable development• Economic reasons• Waste products may be pollutants / greenhouse gases
1[13]
(a) electrons transferred from potassium to sulfur12
two potassium atoms each lose one electron1
forming K+ / 1+ ions1
sulfur atoms gain 2 electrons1
forming S2− / 2− ions1
(b) there are no gaps / sticks between the potassium ions and sulfide ions1
(c) (two) shared pairs between H and S1
rest correct - no additional hydrogen electrons and two non-bonding pairs on sulfur
second mark dependent on first1
(d) 3422
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allow 1 mark for evidence of (2 × 27) + 3[32 + (16 × 4)]
(e) Property Explanation of property
more than one line drawn from a variable negates the mark2
(f) Property Explanation of property
more than one line drawn from a variable negates the mark2
(c) as pressure increases percentage yield increases1
(d) 32−23both readings correct
1
= 9 (%)1
[5]
(a) cotton wool17
(b) all points correct
± ½ small square2
allow 1 mark if 5 or 6 of the points are correct
best fit line
must not deviate towards anomalous point1
(c) (mass)2.1 (g)
allow ecf from drawn best fit line1
(time)100 (s)
1
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(d) a gas is produced1
which escapes from the flask1
(e)
1
0.07 (g / s)
allow ecf answer correctly calculated to 2 decimal places1
(f) collect the gas in a gas syringe1
measured the volume of gas
allow carbon dioxide for gas1
allow for 1 mark
collected gas
or
counted bubbles
(g) The particles have more energy1
The particles move faster1
[14]
(a) because it is a good conductor of electricity.18
(b) (i) 2.1 (%)1
(ii) correct bar for calcium at 3.6 %1
allow error of +/– 0.05%
correct bar for iron at 5.0 %1
allow error of +/– 0.05%
(c) (i) decomposition1
(ii) carbon dioxide1
(iii) carbon = 1
allow one1
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oxygen = 3
allow three1
(iv) 44 (g)
allow forty four1
(d) (i) to make alloys for specific uses.1
(ii) any three from:• to conserve resources of iron or iron ore
allow steel instead of iron or iron oreallow limited resource or non-renewable
• to avoid the need for quarrying/mining• to conserve energy resources or fossil fuels• to limit the amount of carbon dioxide produced or to reduce global warming• to reduce the amount of landfill
“it” = steel
ignore cost and reuse and time and waste3
[13]
(a) (i) (thermal) decomposition
allow decomposes or endothermic1
9
(ii) copper oxide1
(b) (i) the (potassium) carbonate did not decompose/change/react (when heated)
allow temperature not high enough
do not allow potassium did not decompose
ignore references to reactivity1
the mass did not change or the limewater did not go cloudy1
because no carbon dioxide produced1
(ii) the less reactive the metal the more (easily) its carbonate will decompose/react orvice versa
needs to be a relative comparison2
allow max 1 mark where the distinction between a metal and itscarbonate is not clear
allow 1 mark for carbonates of reactive metals do not decompose orvice versa
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(c) (i) make it economical (to extract the metal/iron)
allow make it worth extractingallow so they can make money/profit
1
(ii) Fe1
balanced correctly (2,3,4,3)
not ecf
allow correct balanced equation but with 2Fe2 on right for one mark1
(iii) iron from the blast furnace is brittle1
steel produced is strong / flexible
allow steel has more/specific uses
allow steel is rust-resistant1
“it” = iron
(iv) (recycling) is used to conserve iron (ore) or energy or resources or minimisepollution or reduce the need to quarry
allow reverse arguments.1
(not reuse) because of damage, paint removal, rusting/corrosion, metalfatigue/weaker
1
(not landfill) because sites have limited space or loss of habitats
allow to reduce the use of landfill1
[15]
Marks awarded for this answer will be determined by the Quality of Written Communication(QWC) as well as the standard of the scientific response. Examiners should also apply a ‘best-fit’approach to the marking.
10
Level 3 (5 – 6 marks)There is a description of titrations that would allow a comparison to be made between the twosolutions of hydrochloric acid.
Level 2 (3 – 4 marks)There is a description of an experimental method including addition of acid to alkali which mayinclude an indicator or colour change and may include a measurement of volume.
Level 1 (1 – 2 marks)There is a simple description of using some of the apparatus.
0 marksNo relevant content.
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examples of chemistry points made in the response could include:• acid in burette or flask• alkali/sodium hydroxide or acid in burette or flask• volume of acid or alkali measured using the pipette• indicator in flask• white tile under the flask• slow addition• swirling/mixing• colour change of indicator• burette volume measured
[6]
(a) (i) natural gas
allow fossil fuels / biogas generator1
11
(ii) air contains oxygen1
this would react with / oxidise the hydrogen
allow this would react with / oxidise the iron
ignore nitrogen1
(iii) cooled1
ammonia condenses / liquefies (so can be separated)1
nitrogen and hydrogen (remain as gases and) are returned to the reactor
allow recycled1
(b) (i) 200 °C and 1000 atmospheres1
(ii) the reaction is reversible
allow stated as equilibrium or forward / backward reaction anywherein answer
1
forward reaction is exothermic so increased temperature lowers the yield of ammonia
allow converse1
a lower temperature would decrease rate of reaction
allow converse1
a higher pressure would increase the yield of ammonia because the forward reactionproduces the least number of (gaseous) molecules / moles
allow converse1
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higher pressures would involve high cost / energy1