South Axholme School AS Paper 1 Practical …...South Axholme School Page 1 AS Paper 1 – Practical Questions MARK SCHEME Amount of Substance M1.(a) Stage 1: appreciation that the

South Axholme School

Page 1

AS Paper 1 – Practical Questions MARK SCHEME

Amount of Substance

M1.(a) Stage 1: appreciation that the acid must be in excess and calculation of amount of solid that permits this

Statement that there must be an excess of acid 1

Moles of acid = 50.0 × 0.200 / 1000 = 1.00 × 10–2 mol 1

2 mol of acid react with 1 mol of calcium hydroxide therefore moles of solid weighed out must be less than half the moles of acid = 0.5 × 1.00 × 10–2 = 5.00 × 10–3 mol

1

Mass of solid must be –3 × 74.1 = 1

Stage 2: Experimental method

Measure out 50 cm3 of acid using a pipette and add the weighed amount of solid in a conical flask

1

Titrate against 0.100 (or 0.200) mol dm–3 NaOH added from a burette and record the volume (v) when an added indicator changes colour

1

Stage 3: How to calculate Mr from the experimental data

Moles of calcium hydroxide = 5.00 × 10–3 – (v/2 × conc NaOH) / 1000 = z mol 1

Mr = mass of solid / z 1

Extended response

Maximum of 7 marks for answers which do not show a sustained line of reasoning which is coherent, relevant, substantiated and logically structured.


Page 2

(b) Moles of calcium chloride = 3.56 / 111.1 = 3.204 × 10–2

1

Moles of calcium sulfate = 3.204 × 10–2 × 83.4 / 100 = 2.672 × 10–2

1

Mass of calcium sulfate = 2.672 × 10–2 × 136.2 = 3.6398 = 3.64 (g)

Answer must be to 3 significant figures 1

[11]

M2.(a) Space will fill during titration / titres or volumes added are too high

Do not allow „to improve accuracy‟ without qualification.

Do not allow „incorrect end-point‟ without qualification.

Do not allow „titres or volumes added are too low‟.

Ignore „titres or volumes added are different‟. 1

(b) Less chance of losing liquid on swirling / liquid doesn’t splash on swirling

Do not accept „easier to swirl‟ on its own. 1

(c) (i) Returns reagent on the sides of the flask to the reaction mixture (to ensure that all of the acid / alkali reacts)


Ignore reference to cleaning. 1

(ii) This does not change the number of moles of reagents / water is not a reagent / water is one of the products

Do not allow „water does not affect the titration‟ without qualification.

Ignore „water is neutral / has a pH of 7‟. 1


Page 3

(d) Idea that a single titration could be flawed / anomalous

Do not accept „will improve reliability / reproducibility / accuracy‟ without further qualification.

Allow „to obtain concordant results‟. 1

[5]

M3.Divides percentage by price

Ratios are 1.668, 1.701 and 1.437

Dub-Lit Brick Cleaner is the best value

Allow if divides price by percentage (ratios are 0.600, 0.588 and 0.696).

Lose mark if no working shown or contains an arithmetic error. [1]

M4.(a) (i) Uses sensible scales

Lose this mark if the plotted points do not cover half of the paper.

Lose this mark if the graph plot goes off the squared paper. 1

Plots all of the points correctly ± one small square 1

Draws a best-fit line

Lose this mark if the student‟s line includes either of the points at 0.5 / 0.48 or 3.5 / 2.28

Lose this mark if the student‟s line is doubled or kinked.

Lose this mark if the student‟s line does not pass within one small square of the origin, extending the line if necessary.

1

(ii) 1.38 to 1.47

Allow answer in this range only.

Answer must correspond to value from the student‟s graph. 1

(iii) M1


Page 4

Moles NaOH = 1.00 / 40 and Moles water = (part(b) – 1) / 18

Allow any correct method which uses the answer from part (b). 1

M2 Ratio NaOH : H2O is close to 1:1

Must compare experimental result with theoretical result to score M2.

1

(b) (i) 2NaOH + 2Al + 6H2O → 2NaAl(OH)4 + 3H2

Ignore state symbols. 1

(ii) Pressure build-up due to the production of hydrogen / H2 / gas

Ignore references to the flammability / explosive nature of hydrogen.

1

(c) (Alkali is) corrosive / caustic

Allow „(alkali) burns skin‟.

Ignore „harmful‟, „dangerous‟.

Do not allow „toxic‟ or „irritant‟. 1

[9]

M5.(a) To make sure all the solutions (from both the burette and pipette) react with each other / are in the flask

Penalise „solid‟ or „residue‟.

Do not allow any suggestion of removal of species. 1

(b) Water does not change the number of moles of either reagent / reactants

Water is not a reagent / does not react with either reactant.

Do not allow „water is not involved in the reaction‟.

Apply list principle. 1

[2]


Page 5

M6.(a) ‘Initial mass’ must be the y-axis

If axis unlabelled, use data to decide that „Initial mass‟ is on the

y-axis. 1

Sensible scale

Do not award this mark if plotted points do not cover at least half of the grid.

Do not award this mark if any plotted point is outside the grid. 1

All points plotted correctly

Allow ± one small square. 1

Point at (0,0) is ringed 1

(b) Best-fit straight line that goes through the origin ± ½ small square

Mark consequentially to plotted points but the line must still go through the origin ± ½ small square.

Lose this mark if the line is doubled or kinked.

If the points are plotted correctly, lose this mark if the line deviates towards the anomalies.

1

(c) Students 3 and 5

Allow masses of 1.15 and 1.53 or 2.82 and 3.58

Mark consequentially to plot. 1

(d) Samples 3 or 5 have not lost all their water

Allow reaction / decomposition incomplete. 1

Sample not heated for enough time / larger masses will take a longer time to dehydrate / decompose


Page 6

1

[8]

M7.(a) (CO2 from) burning (fossil) fuels 1

(b) NaCl + CO2 + NH3 + H2O → NaHCO3 + NH4Cl

Allow multiples, including fractions.


(c) CaO + 2NH4Cl → CaCl2 + 2NH3 + H2O


Allow ionic equations.

Do not allow equations involving NH4OH or NH4+ on the right hand

side.


(d) (i) = (106) × 100 / (117 + 100(.1))

Do not penalise precision but must be to minimum of two significant figures.

1

= 48.8

This answer without working scores 1 mark only. 1

(ii) The percentage atom economy cannot be improved

OR

Sell the by-product / CaCl2 (solution)

Do not accept answers which refer to improving the efficiency of the process.

1

(e) It is used up but then regenerated later in the cycle / No overall consumption of NH3

Allow „can act as a catalyst‟.


Page 7

1

[7]

M8.(a) Any three from:

A method of weighing by difference / wash the solid from its weighing container into the beaker

If the nature of any washing is imprecise penalise once only.

Wash the (wet) rod into the flask / beaker after use

Do not allow a method where the solution is made up directly in the flask.

Wash the (wet) beaker into the flask after transfer

Ignore any instructions that refer to rinsing equipment (before use) or use of deionised water.

Wash the filter funnel (after transfer) into the flask

Use a teat pipette to make up to the mark on the volumetric flask

Ensure the bottom of the (liquid) meniscus is on the graduation mark

Mix / shake the final solution in the flask / invert flask Max 3

(b) Do (a) further titration(s)

Mark these points independently. 1

To obtain concordant results

Allow results with ± 0.1 1

[5]

M9.(a) (Returns) reagent on the sides of the flask to the reaction mixture (to ensure that all of the acid / alkali reacts)

Do not allow „to get a better result‟ without qualification.

Do not allow „to ensure that all of the acid / alkali reacts‟ without qualification.

1


Page 8

(b) Water is not a reagent / water one of the products / does not change the number of moles of reagents

Do not allow „water does not affect the titration‟ without qualification.

1

[2]

M10.(a) (i) Mass loss would be too large / water would be lost when heating (so mass incorrect)


Do not allow „water is a product of the reaction‟.

Do not allow „mass of crucible incorrect / too high‟. 1

(ii) Prevents loss of solid / potassium carbonate / potassium hydrogencarbonate (from the crucible)


Do not allow „stops anything escaping‟. 1

(iii) Errors in weighing are too high / percentage errors in (obtaining) the mass are too high

Do not allow „hard to / can‟t weigh very small amounts‟ without further qualification.

1

(b) (i) Mr of KHCO3 is 100(.1)

Do not penalise precision. 1

moles K2CO3 = 1 / (Mr × 2) = 0.005

If factor of 2 missing can only score first mark (M1).

Allow consequential answer on incorrect Mr of KHCO3

1

mass of K2CO3 = 0.005 × 138.2 = 0.69(0)

Correct mass without working scores one mark only (M3). 1

(ii) Reaction / decomposition incomplete


Page 9

Do not allow „a wet crucible was used‟.

Ignore references to impurity and / or experimental errors. 1

[7]

M11.(a) (i) Volume of crater-lake solution on x-axis

Do not penalise missing axes labels.

If axes unlabelled use data to decide.

Lose this mark if axes mis-labelled. 1

Sensible scales

Lose this mark if plotted points do not cover at least half the paper or plot goes off the squared paper.

1

All points plotted correctly +/– one square 1

(ii) Draws appropriate line of best fit, omitting point at 20 cm3 / 15 cm3

Lose this mark if the line deviated towards the anomalous result.

Lose this mark if the candidate‟s line is doubled or kinked.

Candidate does not have to extrapolate to the origin. 1

(iii) 16.5 cm3 +/– 0.5 cm3

Accept this answer only.

Do not mark consequentially on candidate‟s graph. 1

(iv) Value corresponding to 10 cm3 crater-lake solution / 6.00 cm3

Must have correct identity for explanation mark.

Accept results aren‟t concordant. 1

Greatest % error from use of burette

Accept difficult to be accurate with small volumes (owtte). 1


Page 10

(b) (i) pV = nRT

Accept any correct rearrangement.

Ignore case. 1

(ii) V = 81.0 × 10–6 or 8.1 × 10–5

1

n = (1 × 105 × 81.0 × 10–6) / (8.31 × 298)

Mark consequentially on candidate‟s volume. 1

n = 3.27 × 10–3 (mol)

Correct answer without working scores one mark only.

Allow consequential mark using incorrect conversion.

Incorrect units lose this mark. 1

(iii) Mr CaCO3 = 100.1 (M1)

Accept 100 (can score this mark in calculation for M2 and M3). 1

Moles CaCO3 = (3.27 × 10–3 × 10) = 3.27 ×10–2 (M2)

Do not penalise lack of units.

Allow b(ii) × 10

Allow 1.25 × 10–3 × 10 1

Mass CaCO3 = M1 × M2 (= 3.27 g)

Correct mass without working scores one mark only.

Allow 1.25 × 10–2 × 10 × 100.1= 12.5 g 1

(iv) (3.27 / 95) × 100

Accept (b(iii) / 95) × 100.



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3.44 g

Do not penalise lack of units.

Using 12.5 g gives 13.2 g

Correct answer without working scores 2 marks. 1

(v) Abundant / readily available

Accept not caustic or alkaline.

Non-corrosive

Accept insoluble so safe to add in excess (owtte). 1

[17]

M12.Include washings or words to that effect / mix contents

Accept „use distilled / deionised water‟.

Allow „weigh directly into flask‟ if washing included. 1

[1]

M13.(a) 2-6 drops / 0.1-0.3 cm3

Accept „a few drops‟ 1

(b) Incorrect volume recorded / space will fill during titration / produces larger titre value

Do not accept „to give an accurate result‟ without further qualification Do not accept references to contamination

1

[2]

M14.(a) Mass of mineral on x-axis;

If axes unlabelled use data to decide if mass of mineral is on the

x-axis. 1


Page 12

Sensible continuous scales;

Lose this mark if the plotted points do not cover at least 9 squares by 7. Lose this mark if the graph plot goes off the squared paper. The graph does not have to start at the origin.

1

Plots points correctly ± one square;

Award this mark if the line is close to your line. 1

Draws a best fit straight line

Award this mark if best fit line is consistent with candidate‟s plotted points. Lose this mark if line is kinked or doubled.

1

(b) 1.48 or 1.49 or 1.50 or 1.5 (g);

Accept these answers only Ignore precision of answer. Allow range 1.48 – 1.5

1

(c) 0.0124 (mol);

Accept 0.012, 0.0125. Allow answer without working.

1

(d) (1.49 / 0.0124) = 119.4 – 125.0;

Must divide answer to part (b) by answer to part (c) to score first mark. Allow consequential answer from part (b). Allow answer without working. Ignore precision of answer.

1

(e) Answer to part (e) close to 120.3;

Allow consequential answer from part (d).

Allow correct calculation of x 1


Page 13

(f) x must be a whole number; 1

(g) Good / straight line so results good / reliable;

Allow consequential answers from candidate‟s graph Do not allow „so results are accurate‟.

1

Anomaly at 1.34 g;

Allow anomaly clearly indicated on the graph. 1

(h) Ensure reaction / decomposition goes to completion;

Do not allow „to make fair test‟ or „improve reliability‟ Accept to „remove all carbon dioxide and water‟.

1

(i) (i) Percentage errors too high / errors in weighing too high;

Do not allow „to make fair test‟ or „improve reliability‟ Do not allow „errors‟ on its own.

1

(ii) Incomplete decomposition or words to that effect;

Do not allow „to make fair test‟ or „improve reliability‟ Do not allow „takes too long‟ or „wastes chemicals‟ Do not allow „not all of the water removed‟.

1

(j) 39.05 / 18 = 2.170 and 60.95 / 84.3 = 0.723;

Allow Mr of MgCO3.H2O = 138.3 1

MgCO3.3H2O;

54 / 138.3 + 39.05% MgCO3.3H2O without working scores 1 mark.

1

(k) Atom economy for Reaction 1 is (40.3 / 84.3) x 100 = 47.8%

Maximum 1 mark if no working.


Page 14

Ignore precision of answers. 1

Atom economy for Reaction 2 is (40.3 / 58.3) x 100 = 69.1% 1

(l) No gas produced in stomach / won’t cause wind;

Do not allow „gas produced‟ on its own. 1

[19]

Bonding Currently no practical questions Energetics

M1.(a) Start a clock when KCl is added to water 1

Record the temperature every subsequent minute for about 5 minutes

Allow record the temperature at regular time intervals untilsome time after all the solid has dissolved for M2

1

Plot a graph of temperature vs time 1

Extrapolate back to time of mixing = 0 and determine the temperature 1

(b) Heat taken in = m × c × ΔT = 50 × 4.18 × 5.4 = 1128.6 J

Max 2 if 14.6 °C used as ΔT 1

Moles of KCl = 5.00 / 74.6 = 0.0670 1


Page 15

Enthalpy change per mole = +1128.6 / 0.0670 = 16 839 J mol-1

1

= +16.8 (kJ mol-1)

Answer must be given to this precision 1

(c) ΔHsolution = ΔHlattice + ΔH(hydration of calcium ions) + 2 × ΔH(hydration of chloride ions)

ΔHlattice = ΔHsolution – ΔH(hydration of calcium ions) –2 ×ΔH(hydration of chloride ions) 1

ΔHlattice = –82–9 – (–1650 + 2 × –364) = +2295 (kJ mol–1) 1

(d) Magnesium ion is smaller than the calcium ion 1

Therefore, it attracts the chloride ion more strongly / stronger ionic bonding 1

[12]

M2.(a) Temperature on y-axis

If axes unlabelled use data to decide that temperature is on y-axis. 1

Uses sensible scales

Lose this mark if the plotted points do not cover half of the paper.

Lose this mark if the temperature axis starts at 0 °C. 1

Plots all of the points correctly ± one square

Lose this mark if the graph plot goes off the squared paper. 1


Page 16

Draws two best-fit lines

Candidate must draw two correct lines.

Lose this mark if the candidate‟s line is doubled or kinked. 1

Both extrapolations are correct to the 4th minute

Award this mark if the candidate‟s extrapolations are within one square of your extrapolations of the candidate‟s best-fit lines at the 4th minute.

1

(b) 19.5 (°C)

Accept this answer only. 1

(c) 26.5 ± 0.2 (°C)


(d) (c) – (b)

Only award this mark if temperature rise is recorded to 1 d.p. 1

(e) Uses mcΔT equation

Allow use of this equation with symbols or values for M1 even if the mass is wrong.

1

Correct value using 25 × 4.18 × (d)

7.0 gives 732 J.

Correct answer with no working scores one mark only.

Do not penalise precision.

Allow answer in J or kJ.

Ignore sign of enthalpy change. 1

(f) 9.0(1) × 10–3

Do not allow 0.01

Allow 9 × 10–3 or 0.009 in this case. 1


Page 17

(g) If answer to (e) in J, then (e) / (1000 × (f))

or

If answer to (e) in kJ, then (e) / (f)

7.0 and 9.01 × 10–3 gives 81.2 kJ mol–1

If answer to (e) is in J must convert to kJ mol–1 correctly to score mark.

1

Enthalpy change has negative sign

Award this mark independently, whatever the calculated value of the enthalpy change.

1

(h) The idea that this ensures that all of the solution is at the same temperature

Do not allow „to get an accurate reading‟ without qualification. 1

(i) (i) Chlorine is toxic / poisonous / corrosive

Do not allow „harmful‟. 1

(ii) Explosion risk / apparatus will fly apart / stopper will come out

Ignore „gas can‟t escape‟ or „gas can‟t enter the tube‟. 1

[16]

Kc and Equilbria

M1.(a) = (0.0745) × (0.0813) / (0.0424) × (0.0525) = 2.72

Allow answer only without working if correct.

Lose this mark if the wrong Kc expression is used. 1

Answer, whether or not correct, given to three significant figs

Do not expect conversion from moles to concentration but allow if shown.

1


Page 18

(b) Less acid is present (so less NaOH needed) 1

Equilibrium would shift to right (side with more ester / less acid) 1

[4]

M2.(a) Kc / Ka / equilibrium constant / constant is temperature dependent

Do not allow „affects or shifts equilibrium‟. 1

(b) Thermostat / water bath 1

[2]

Atomic Structure Currently no practical questions. Periodicity Currently no practical questions. Redox, Group 2 and Group 7

M1.(a) (i) SrCl2(aq) + Na2SO4(aq) → SrSO4(s) + 2NaCl(aq)


Allow ionic equations.

Lose this mark if any of the state symbols are missing or incorrect. 1

(ii) Add nitric acid to the mixture (until in excess)

Do not allow any suggestion that the solution is an emetic. 1

Filter (to isolate strontium sulfate) 1

(b) Insoluble barium sulfate is formed

Allow „removes barium ions as a precipitate‟. 1


Page 19

(c) Add silver nitrate, then dilute ammonia (solution) M1

Do not allow answers which imply silver nitrate and ammonia are added at the same time.

Allow „add silver nitrate, then concentrated ammonia (solution)‟.

Can score M1 in the answer for M3 1

Cream precipitate M2

Allow „off white precipitate‟. 1

No visible change or precipitate dissolves slightly in dilute ammonia M3

Allow „soluble / colourless solution / precipitate dissolves in concentrated ammonia‟.

Allow 3 marks for:

Add dilute ammonia (solution), then silver nitrate M1

No visible change M2

Cream / off white precipitate with silver nitrate M3 1

[7]

M2.(a) (i) 1.08 × 10–2

Do not penalise precision but must be to at least 2 significant figures.

Do not accept 1 × 10–2

1

(ii) 5.4(0) × 10–3

Allow (i) / 2

Do not penalise precision but must be to at least 2 significant figures.

1

(iii) 266.6

Lose this mark if answer not given to 1 decimal place. 1


Page 20

(iv) mass = 5.4(0) × 10–3 × 266.6 = 1.44 g M1

Allow (ii) × (iii). 1

percentage = 1.44 × 100 / 2.25 = 64.0 M2

Allow consequential answer from M1

Lose this mark if answer not given to 3 significant figures.

Correct answer with no working scores M2 only. 1

(v) 1 Would give an incorrect / too large mass (of silver chloride)

Do not allow „to get an accurate result‟ without qualification. 1

2 To remove soluble impurities / excess silver nitrate (solution) / strontium nitrate (solution)

Do not allow „to remove impurities‟.

Do not allow „to remove excess strontium chloride solution‟. 1

(b) (i) Mg2+(aq) + 2OH-(aq) → Mg(OH)2(s)

Allow Mg2+(aq) + 2OH-(aq) → Mg2+(OH-)2(s)


Lose mark if state symbols are missing or incorrect.

Lose mark if incorrect charge on an ion. 1

(ii) Does not produce CO2 / gas which distends stomach / does not produce wind / does not increase pressure in stomach

Allow „prevents flatulence‟ and „prevents burping‟.

Do not allow „gas‟ without qualification. 1

(c) (CH3COO)2Ca → CH3COCH3 + CaCO3

Allow multiples.

Allow propanone as C3H6O

Allow (CH3COO-)2Ca2+ → CH3COCH3 + Ca2+CO32-

1


Page 21

(d) Ca (salt) - no visible change with sodium chromate(VI) M1

Allow „yellow solution formed‟ or „no ppt. forms‟.

Allow M1 and M2 in any order. 1

Sr and Ba (salts) give (yellow) precipitate with sodium chromate(VI) M2

Lose this mark if precipitate has an incorrect colour. 1

Sr precipitate (chromate(VI)) dissolves in ethanoic acid / Ba precipitate (chromate(VI)) does not dissolve in ethanoic acid M3

If ethanoic acid is added first, allow access to M1 and M3. 1

(e) C 42.09 / 12, H 2.92 / 1, N 8.18 / 14, O 37.42 / 16 and S 9.39 / 32.1

Accept any other correct method of working.

If relative atomic mass has been divided by the percentage composition is used then CE = 0 / 2

1

C12H10N2O8S

Correct answer with no working scores 1 mark only. 1

[15]

M3.Mg2+ and Cl–

Do not allow names. [1]

M4. (a) (i) M1 (yellow precipitate is) silver iodide OR AgI (which may be awarded from the equation)

M2 Ag+ + I– → AgI (Also scores M1 unless contradicted)

M3 sodium chloride OR NaCl

For M2

Accept multiples

Ignore state symbols


Page 22

Allow crossed out nitrate ions, but penalise if not crossed out 3

(ii) The silver nitrate is acidified to

• react with / remove ions that would interfere with the test

• prevent the formation of other silver precipitates / insoluble silver compounds that would interfere with the test

• remove (other) ions that react with the silver nitrate

• react with / remove carbonate / hydroxide / sulfite (ions)

Ignore reference to “false positive” 1

(iii) M1 and M2 in either order

–F (ion) OR Fluoride M1

is soluble / dissolves (in water) Silver fluoride / AgF • M2

change no visible /observablewould form / no precipitate •

Do not penalise the spelling “fluoride”,

Penalise “fluride” once only

Mark M1 and M2 independently 2

(b) M1 Ba2+ + SO42- → BaSO4

(or the ions together)

white precipitate / white solid / white suspension M2

M3 Barium meal or ( internal ) X-ray or to block X-rays

therefore not toxic) (and / barium sulfate is insoluble 4BaSO M4

For M1, ignore state symbols

Allow crossed out sodium ions, but penalise if not crossed out

For M2, ignore “milky”

M4, penalise once only andOR BaS used in M1 3If BaSO

For M3 Ignore radio-tracing

For M4 NOT barium ions

NOT barium

NOT barium meal

4BaSO clearlyIt” unless “NOT

4


Page 23

(1.00794) = 28.0317640) + .0000(122M1 (c)

M2 Ethene and CO or “they” have an imprecise Mr of 28.0 / 28

OR

.to one d.p rMsame they” have the “Ethene and CO or

OR

These may be shown by two clear, simple sums identifying both compounds

M3 C2H4 + 2O2 → 2CO + 2H2O

(H2C=CH2)

M4 Displayed formula

(polymer) AdditionType of polymer = M5

M1 must show working using 5 d.p.for hydrogen

imprecise , if this refers to the ”close to“or ”similar“Penalise ”the same“, since this does not mean value in M2

For M3, accept CH2=CH2 OR CH2CH2

must be drawn out including those on either side all bondsFor M4, of the unit.

Penalise “sticks”

Ignore brackets around correct repeating unit but penalise “n”

Penalise “additional” 5

[15]

M5.(a) Hydrochloric acid = C 1


Page 24

Barium chloride = A 1

(b) Barium sulfate is insoluble 1

CuSO4 + BaCl2 → BaSO4 + CuCl2

Accept multiples.

Accept ionic equation.

Do not penalise lack of state symbols, but if used they must be correct.

1

(c) CO2 / Carbon dioxide 1

(d) Reagent 1 silver nitrate (solution)

Ignore lack of reference to acidifying prior to addition of silver nitrate solution.

1

White precipitateObservation 1 1

Reagent 2 (dilute) ammonia solution / aqueous ammonia

Do not accept addition of ammonia only. 1

Observation 2 (Colourless) solution

Allow ppt dissolves.

Do not allow „goes colourless‟ or „goes clear‟.

Chlorine and no visible change or solution does not

become orange scores M3 and M4. 1


Page 25

(e) Gloves / wash hands after use

Ignore „eye protection‟.

Do not accept „do not ingest the chemicals‟, „wipe up spillages‟, „use a fume cupboard‟, „wear a lab coat‟ (list principle).

1

[10]

M6.(a) (i) Blue to green

Accept blue to yellow. 1

(ii) Decrease / less acid needed

Ignore references to rate 1

(iii) Gloves or avoid skin contact

Allow „if reagent contacts skin wash off (immediately)‟ or answers to that effect.

Do not accept „wash‟ only.

Ignore „eye protection‟ or „lab coat‟ or „use of fume cupboard‟ or „don‟t ingest‟.

1

(iv) Less chance of losing liquid on swirling / liquid doesn’t splash on swirling

Do not accept „easier to swirl‟ on its own.

Do not accept „easier to stir‟. 1

(v) Idea that a single titration could be flawed / anomalous

Allow an indication that the first titration is a rough titration.


Do not allow vague references to „outliers‟. 1

(b) (i) 2.3(3) × 10–2

Do not penalise additional significant figures, but do not allow 0.02 1


Page 26

(ii) Dilution of acid needed / may react with carbon dioxide in air

Accept „poor end-point‟ or „no suitable indicator‟ or „a large volume (of calcium hydroxide) will be needed‟.

Ignore references to low solubility or concentration too low. 1

[7]

solid excessRemove undissolved barium hydroxide / (a)M7.

Do not accept „remove impurities‟. 1

(b) Filtration

Do not accept „decanting‟ or „sieving‟.

Ignore references to heating or drying. 1

(c) Remove (excess) sulfuric acid 1

(d) Ba(OH)2 + H2SO4 → BaSO4 + 2H2O

Accept multiples.

Accept Ba2+ + SO42- → BaSO4


(e) (i) 233.4

Accept 233 1

(ii) 0.018(2)

Do not penalise additional significant figures, but do not allow 0.02

Allow consequential answer from (i). 1

(iii) 0.018(2) ×171.3 = 3.12


If 0.018 used, answer = 3.08 1


Page 27

×10 = 31.2


Allow this mark if 0.18(2) used directly.

Correct answer without working scores one mark only.

Allow consequential answer on (ii) 1

(f) Barium sulfate / it is insoluble

Do not accept answers based on small amount ingested.

Do not accept barium. 1

[9]

M8.(a) sulfuric acid / H2SO4

1

(b) hydriodic acid / HI OR hydrobromic acid / HBr 1

(c) add dilute ammonia solution

Notes * do not allow „concentrated ammonia‟ or „ammonia’

1

precipitate / ppt disappears / dissolves OR colourless solution forms 1

(d) would react with the acid / no gas evolved in tests 1

[5]

M9.Add (hydrochloric) acid to the mixture;

acid. Allow correct acid eg nitric


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1

to isolate strontium sulphate; Filter

Do not allow „drain‟ or decant‟ 1

[2]

M10.(a) 2NaBr + 2H2SO4 Na2SO4 + Br2 + SO2 + 2H2O

Allow ionic equation

2Br– + 2H2SO4 Br2 + SO42– + SO2 + 2H2O

1

Br– ions are bigger than Cl– ions 1

Therefore Br– ions more easily oxidised / lose an electron more easily (than Cl– ions) 1

(b) This question is marked using levels of response. Refer to the Mark Scheme Instructions for Examiners for guidance on how to mark this question.

Level 3

All stages are covered and the explanation of each stage is generally correct and virtually complete. Stages 1 and 2 are supported by correct equations.

Answer communicates the whole process coherently and shows a logical progression from stage 1 to stage 2 and then stage 3. The steps in stage 3 are in a logical order.

5–6 marks

Level 2

All stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies OR two stages are covered and the explanations are generally correct and virtually complete.

Answer is mainly coherent and shows a progression through the stages. Some steps in each stage may be out of order and incomplete.

3–4 marks


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Level 1

Two stages are covered but the explanation of each stage may be incomplete or may contain inaccuracies, OR only one stage is covered but the explanation is generally correct and virtually complete.

Answer includes some isolated statements, but these are not presented in a logical order or show confused reasoning.

1–2 marks

Level 0

Insufficient correct chemistry to warrant a mark. 0 marks

Indicative chemistry content

Stage 1: formation of precipitates

• Add silver nitrate • to form precipitates of AgCl and AgBr • AgNO3 + NaCl → AgCl + NaNO3

• AgNO3 + NaBr → AgBr + NaNO3

Stage 2: selective dissolving of AgCl

• Add excess of dilute ammonia to the mixture of precipitates • the silver chloride precipitate dissolves • AgCl + 2NH3 → Ag(NH3)2

+ + Cl−

Stage 3: separation and purification of AgBr

• Filter off the remaining silver bromide precipitate • Wash to remove soluble compounds • Dry to remove water

6

(c) Cl2 + 2HO– OCl– + Cl– + H2O 1

OCl– is +1

Cl– is –1

Both required for the mark 1

[11]

M11. (a) (i) M1 iodine OR I2 OR I3–


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Ignore state symbols

Credit M1 for “iodine solution”

M2 Cl2 + 2I – 2Cl – + I2

OR ½ Cl2 + I – Cl – + ½ I2

Penalise multiples in M2 except those shown

M2 accept correct use of I3–

M3 redox or reduction-oxidation or displacement 3

silver chloride(the white precipitate is) M1 (ii)

ignore incorrect formula this markand for must be named M1

M2 Ag+ + Cl – AgCl

For M2 ignore state symbols

Penalise multiples

it dissolves(white) precipitate / M3

colourless solution OR

Ignore references to “clear” alone 3

(b) (i) M1 H2SO4 + 2Cl – 2HCl + SO42–

For M1 ignore state symbols

OR H2SO4 + Cl– HCl + HSO4–

Penalise multiples for equations and apply the list principle

OR H+ + Cl– HCl

M2 hydrogen chloride OR HCl OR hydrochloric acid 2

(ii) M1 and M2 in either order

For M1 and M2, ignore state symbols and credit multiples

M1 2I – I2 + 2e –

OR

8I – 4I2 + 8e –

Do not penalise absence of charge on the electron

Credit electrons shown correctly on the other side of each equation

M2 H2SO4 + 8H+ + 8e – H2S + 4H2O


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OR

SO42– + 10H+ + 8e – H2S + 4H2O

Additional equations should not contradict

(ions) oxidises the iodide/ oxidising agent M3

OR

electron acceptor

M4 sulfur OR S OR S2 OR S8 OR sulphur 4

/ (sodium) hydroxide reacts with / neutralises the –NaOH / OHThe M1 (iii) (lowering its concentration) / acid / HBr +H

OR a correct neutralisation equation for H+ or HBr with NaOH or with hydroxide ion

Ignore reference to NaOH reacting with bromide ions

Ignore reference to NaOH reacting with HBrO alone

M2 Requires a correct statement for M1

(from L to R)equilibrium moves / shiftsThe (position of)

/ acid / HBr that has been removed / lost +replace the Hto •

/ acid / HBr concentration +increase the Hto OR •

/ acid / HBr / product(s) +make more Hto OR •

/ loss of product(s) +oppose the loss of Hto OR •

of product(s) crease in concentrationoppose the deto OR •

equilibrium In M2, answers must refer to the (position of) and is not enough to state simply that it / the shifts / moves

system / the reaction shifts to oppose the change.

M3 The (health) benefit outweighs the risk or wtte

OR

a clear statement that once it has done its job, little of it remains

OR

used in (very) dilute concentrations / small amounts / low doses 3

[15]


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M12. (a) NaBr ONLY

Penalise incorrect case or additional formulae. Ignore names

1

(b) NaF ONLY


1

from either ONLY one (c) NaF

OR

NaCl


1

(d) NaI ONLY


1

[4]

M13.(a) Increase 1

Van der Waal’s forces between molecules 1

Increase with size (or Mr or surface area etc) 1

More energy needed to break (overcome) these forces

(Note max 2 from last three marks if no mention of molecules or ‘molecular’)

1

(b) (i) Brown solution (or yellow or orange)


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1

Cl2 + 2Br → 2C1– + Br2

1

(ii) cream precipitate 1

Br– + Ag+ → AgBr 1

Precipitate dissolves 1

(iii) orange (brown) fumes (gas), White fumes (or misty fumes), choking gas (any 2)

2

(c) 2H+ + H2SO4 + 2Br– → SO2 + Br2 + 2H2O (SO2 and Br2 (1), equation (1))

2

[13]

South Axholme School AS Paper 1 Practical …...South Axholme School Page 1 AS Paper 1 – Practical Questions MARK SCHEME Amount of Substance M1.(a) Stage 1: appreciation that the

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