Chemical Analysis Mark schemes

Q1.

(a) Air

2

Steel

1

(b)

Allow 1 mark for the correct meanings linked to context but incorrect way around

1

(c) Damp litmus paper turns white

1

(d) Iron(III)

1

[6]

Q2.

(a) The start line was drawn in ink

1

The water level was above the spots

1

(b) 3

1

(c) A

1

(d) (distance moved by dye A) 38 (mm)

allow values in range 36-40

1

(distance from start line to solvent front)

102 (mm)

allow values in range 101-103

1

allow ecf from Table 1

1

0.37254 …

allow values in range 0.35 − 0.39

1

0.37

1

accept 0.37 with no working shown for 5 marks

[9]

Q3.

(a) filtration

or

by passing through filter beds to remove solids

1

sterilisation to kill microbes

allow chlorine / ozone allow ultraviolet light

1

(b) water needs more / different processes

1

because it contains any two from:

• more organic matter

• more microbes

• toxic chemicals or detergents

2

(c) (as part of glassware attached to bung)

salt solution in (conical) flask

allow suitable alternative equipment, eg boiling tube

1

(at end of delivery tube)

pure water in test tube which must not be sealed

allow suitable alternative equipment, eg, beaker, condenser

1

heat source (to heat container holding salt solution)

1

if no other mark obtained allow for 1 mark suitable equipment drawn as part of glassware attached to bung and at end of delivery tube

(d) determine boiling point

1

should be at a fixed temperature 100°C

allow should be 100°C

allow if impure will boil at a temperature over 100°C

1

(e) high energy requirement

1

[11]

Q4.

(a) water level above the start line

and

start line drawn in ink

allow water level too high

1

water level

food colours would dissolve into water

or

start line

the ink would ‘run’ on the paper

1

(b) (distance moved by A) 2.8cm and 8.2 cm (distance moved by solvent)

allow values in range 2.7 − 2.9 cm and 8.1 − 8.3 cm

1

1

0.34

allow 0.33 or 0.35

allow ecf from incorrect measurement to final answer for 2 marks if given to 2 significant figures

accept 0.34 without working shown for 3 marks

1

(c) 6.6 cm

allow values between 6.48 and 6.64 cm

1

(d) solvent moves through paper

1

different dyes have different solubilities in solvent

1

and different attractions for the paper

1

and so are carried different distances

1

(e) calcium ions

allow Ca2+

1

sodium ions

allow Na+

1

(f) two different colours

or

Ca2+ / one is orange-red and Na+ / the other is yellow

allow brick red for Ca2+ and / or orange for Na+

allow incorrect colours if consistent with answer to 7.5

1

(so) colours mix

or

(so) one colour masks the other

1

(g) (Student A was incorrect)

because sodium compounds are white not green

or

because sodium carbonate is soluble

1

so can’t contain sodium ions

1

(Student B was incorrect)

because adding acid to carbonate produces carbon dioxide

1

so must contain carbonate not chloride ions

1

[18]

Q5.

(a) ammonia and nitric acid

allow NH4OH

allow NH3(aq)

1

(b) shows fertilisers are formulations

allow gives percentage / proportion of nitrogen, phosphorus and potassium in the fertiliser

1

(so) farmers can choose fertiliser with required properties

1

(c) as world population increases, ammonia production increases

1

ammonia is used to produce fertilisers

1

so increasing need for fertilisers as more food required for increased population

allow as more food produced less mortality

1

[6]

Q6.

(a) fermentation

1

(b) (i) turns cloudy / milky / white

ignore bubbles

1

because carbon dioxide is produced

allow CO2 produced

1

(ii) filter paper

1

[4]

Q7.

(a) (i) fizz / effervescence / bubbles

allow calcium carbonate decreases in size or dissolves

1

because carbon dioxide produced / released

allow because gas produced / released

1

limewater turns cloudy / milky / white

1

because (a precipitate of or solid) calcium carbonate forms

allow because of carbon dioxide if not already credited

1

(ii)

allow -OH

do not allow lower case ‘h’

1

(iii) acid

must be in this order

ignore any name of an acid

1

ester(s)

1

(b) white (precipitate) no change

no change no change

all four correct 2 marks

any two correct 1 mark

2

(c) (i) lilac

allow purple

1

red

1

must be in this order

(ii) colours are masked / changed by each flame colour

1

[12]

Q8.

(a) (i) Filtration

1

(ii) Chlorine

1

(b) (i) nanoparticles are small / smaller / much smaller / tiny

allow any in range 1−100 nm or 1 × 10-9 m − 1 × 10-7 m or a few hundred atoms in size

ignore numbers if stated smaller

1

(ii) they have a high surface area to volume ratio

reference to surface area without volume ratio is insufficient

allow nanoparticles are very reactive or nanoparticles are more reactive than normal particles.

1

(c) (sodium hydroxide) produces a white precipitate

accept solid / suspension or ppt or ppte for precipitate.

ignore cloudy / milky

1

which (then) dissolves / disappears (in excess sodium hydroxide)

M2 cannot be awarded unless a solid of some sort has been made

ignore names or formulae of compounds

1

[6]

Q9.

(a) (i) Proton

1

(ii) Neutron

1

(b) In order of increasing atomic number

1

(c) (i) 9

1

(ii) Gas

1

(d) (i) gains (one) electron

1

(to gain a) full outer energy level or noble gas configuration

allow because it has seven outer electrons

1

(ii) add sodium hydroxide (solution)

allow ammonia (solution) or ammonium hydroxide or any other soluble hydroxide or flame test

1

(forms a) blue precipitate

second mark dependent on suitable reagent being added

allow blue−green / blue / green if flame test given

1

[9]

Q10.

(a) copper (II) → blue

iron (III) → brown

more than one line from any box negates the mark

1

1

(b) aluminium

allow correct answer shown in box if answer line blank

1

(c) (i) yellow

allow orange

1

(ii) lilac

allow purple

1

(iii) one colour masks the other

allow colours mixed

1

[6]

Q11.

(a) X:

Fe2+ / iron(II), SO42- / sulfate

allow iron(II) sulfate

or FeSO4

1

Y:

Na+ / sodium, I- / iodide

allow sodium iodide

or NaI

1

Z:

Fe3+ / iron(III), Br- / bromide

allow iron(III) bromide

or FeBr3

correct identification of any two ions = one mark

correct identification of any four ions = two marks

1

(b) any five from:

allow converse arguments

method 1

• weighing is accurate

• not all barium sulfate may be precipitated

• precipitate may be lost

• precipitate may not be dry

• takes longer

• requires energy

allow not all the barium hydroxide has reacted

method 2

• accurate

• works for low concentrations

allow reliable / precise

5

[8]

Q12.

(a) (i) Solids

1

(ii) Chlorine

1

(iii) improves dental health or reduces tooth decay

1

(b) put a sample of the filtered water in an evaporating basin or leave to evaporate

accept any description of evaporation (using a Bunsen or leaving on the windowsill)

1

there will be crystals of salt left

1

(c) sodium and / or chloride ions are bigger than water (molecules) or ions are charged or molecules are not charged

do not accept sodium chloride molecules as ions is given in the question

1

[6]

Q13.

(a) start line drawn in ink

1

so it will run / dissolve in the solvent / split up

allow mixes with the spots

1

spots under solvent or solvent above spots / start line

1

so they will mix with solvent or wash off paper or colour the solvent or dissolve in the solvent

1

(b) (i) contains A and E

1

and one other (unknown substance)

if no other marks awarded, an answer saying it is made up of three colours gains 1 mark

1

(ii) 45 or 46

allow any value from 45 to 46

1

18

allow any value from 16 to 20

award 1 mark if numbers correct but in cm

1

(iii) 0.40

allow ecf from (b)(ii)

ignore units

1

(c) fast red

allow ecf from (b)(iii)

1

has same Rf value

allow none of them, as none has the same Rf value for 2 marks

1

(d) any one from:

• more accurate

• more sensitive

• uses small quantities of samples

• quicker / faster / more rapid

• can link to mass spectrometer (MS)

1

[12]

Q14.

(a) (i) ionic (bonding)

1

(ii) ions cannot move in solid or are in fixed positions

do not accept electrons / atoms / molecules

ignore particles

must mention ions

1

but can move in solution

1

(b) silver chloride formed

1

which is insoluble

1

(c) (i) aluminium

1

calcium

accept other metal ions that also give white precipitates (such as lead and zinc)

1

(ii) add excess sodium hydroxide solution

the second mark of each pair is dependent on the first mark being awarded.

1

precipitate remains

1

carry out a flame test

1

not red / orange

accept any colour that is not orange / red

give full credit for answers that correctly eliminate other cations in (c)(i) that would give white precipitates with a few drops of NaOH

1

[11]

Q15.

Marks awarded for this answer will be determined by the Quality of Communication (QC) as well as the standard of the scientific response. Examiners should also apply a ‘best-fit’ approach to the marking.

0 marks

No relevant content

Level 1 (1 – 2 marks)

Any description of a method used and / or a result given

Level 2 (3 – 4 marks)

Description of workable methods used, with results to identify positive or negative ions

Level 3 (5 – 6 marks)

Description of methods used to identify both positive and negative ions, with relevant results

examples of the points made in the response

extra information

Test: add (platinum / nichrome) wire (for the flame test)

accept any method of introducing the solution into the flame, eg a splint soaked in the solution or sprayed from a bottle

Result: the sodium compounds result in a yellow / orange / gold flame or the potassium compound results in a lilac / purple / mauve flame

student could state that potassium carbonate gives a different colour to the three sodium compounds as long as it is clear that the flame test colour comes from Na+ or K+

Test: add dilute nitric acid to all four solutions

allow any acid

Result: sodium carbonate and potassium carbonate will effervesce or sodium chloride and sodium iodide will not effervesce

Test: add dilute nitric acid followed by silver nitrate

Result: sodium chloride and sodium iodide produce a precipitate or sodium chloride produces a white precipitate and sodium iodide produces a yellow precipitate

accept sodium carbonate and potassium carbonate do not produce a precipitate

[6]

Q16.

(a) (i) copper is less reactive than hydrogen or copper is unreactive

1

(ii) Zinc and dilute hydrochloric acid

1

(b) (gas) syringe

1

(c) (i) 35

allow 3

1

because not close to others

accept it is much lower than the others

ignore references to trends or patterns

dependent on the first mark

1

(ii) (49 + 50 + 48) / 3

= 49

correct answer with or without working gains 2 marks

1

allow ecf from anomaly identified in (i) for 2 marks:

• Exp 1 anomalous gives 43.3

• Exp. 2 anomalous gives 44

• Exp. 4 anomalous gives 44.7

answer of 45.5 or 46 (anomaly not excluded) gains 1 mark

correct working excluding anomaly but with wrong answer gains 1 mark

1

(iii) so that a mean can be calculated

accept improves accuracy of the mean or so anomalies can be identified / discarded or to reduce effect of random errors

ignore makes it a fair test

ignore reliability, validity, repeatability, reproducibility

1

(d) (i) idea of mixing with oxygen / air, letting air / oxygen in

accept converse

1

(ii) H2O

do not accept incorrect additional products

1

balancing 2 … (1) … 2

allow fractions or multiples

dependent on first mark

1

[11]

Q17.

(a) (i) (phosphoric) acid

allow phosphoric

1

(ii) H+ / hydrogen (ion)

if ion symbol given, charge must be correct

1

(b) (i) pencil

1

so it will not run / smudge / dissolve

ignore pencil will not interfere with / affect the results

or

because ink would run / smudge / dissolve

ignore ink will interfere with / affect the results

1

(ii) any three from:

reference to spots / dots = max 2

allow colouring for colour

• 3 colours in Cola

allow more colours in cola or fewer colours in fruit drink

• 2 colours in Fruit drink

• one of the colours is the same

• two of the colours in Cola are different

• one of the colours in Fruit drink is different

allow some of the colours in the drinks are different

• one of the colours in Cola is the most soluble

accept one of the colours in Cola has the highest Rf value

3

(c) different substances travel at different speeds or have different retention times

accept different attraction to solid

ignore properties of compounds

1

(d) (i) Is there caffeine in a certain brand of drink?

1

(ii) any two from:

• cannot be done by experiment

• based on opinion / lifestyle choice

• ethical, social or economic issue

accept caffeine has different effects on different people

2

[11]

Q18.

(a) (i) method of introducing sample into flame

e.g. wire / splint / spray

1

clean wire or colourless flame

allow blue / roaring flame

1

(ii)

1

1

(iii) (potassium) chloride

allow KCl or Cl–

1

(b) (i) copper

allow Cu2+

1

(ii) sulfate

1

[7]

Q19.

(a) lithium

allow Li+ / Li

1

yellow

allow orange

1

(b) silver nitrate (solution)

incorrect test = 0 marks

ignore (nitric) acid

do not allow other named acids

1

white precipitate

1

(c) blue precipitate (with sodium hydroxide) indicates copper ions

allow Cu2+

1

and white precipitate (with barium chloride) indicates sulfate ions

allow SO42-

accept compound X is copper sulfate / CuSO4 for 1 mark

1

but iron(II) ions produce a green precipitate (with sodium hydroxide)

1

[7]

Q20.

(a) time from when the heating is started until

1

the limewater turns cloudy / milky

1

(b) (i) the temperature was not high enough

accept the copper carbonate had not started to decompose / react

accept it takes time to heat up the copper carbonate

1

the bubbles of gas were air

accept no carbon dioxide produced

1

(ii) the copper carbonate was decomposing / reacting

accept the temperature was high enough to cause decomposition / a reaction

1

so carbon dioxide was produced

allow correct word / symbol equation

1

(iii) copper oxide was produced

allow correct word / symbol equation

1

because the copper carbonate had completely decomposed / reacted

ignore all of the carbon dioxide had been given off

1

[8]

Q21.

(a) additive

1

(b) colour 3 is a mixture of colours 1 and 2

any two from:

accept E-number or additive instead of colour

ignore comments about height / level

1

• colour 1 is made up of only one colour / dye

• colour 2 is made up of only one colour / dye

• colour 3 is made up of two colours / dyes

or

more colours (than colours 1 and 2)

2

[4]

Q22.

(a) any two from:

ignore reference to taste / shelf-life / sales etc

• improve the colour / appearance

• additives are permitted / not banned / listed on the label

• link between additives and hyperactivity not proved

• maintain the low cost of the drink or natural colours would make the drink cost more

allow cheaper if qualified

2

(b) have a control group / placebo or test children before any drink given

1

give a drink to at least 3 groups or give a drink at least 3 times

1

give each additive to different group / children / at different times

1

observe / monitor / compare behaviour of group / children

1

(c) (i) so that there would be trust / respect / no bias

1

(ii) compare the colours / spots from the orange drink with those of the (three) additives

accept diagram of chromatogram(s) with spots for E102, 104, 110 and sample from the orange drink

1

there should be no matching colours / spots

1

[9]

Q23.

(a) (i) so there are no impurities

accept no other chemicals / not contaminated

allow to get the correct result

1

(ii) high melting point

1

unreactive

1

(iii) yellow-orange

1

(b) (i) bubbles / fizz / effervescence

ignore any named gas

1

(ii) milky

1

(c) fast(er)

1

small(er) amount

1

[8]

Q24.

(a) (i) Na2CO3: HCl → gas / effervescence / bubbles (1)

CO2 / carbon dioxide / turns lime water milky (1)

1

NaCl: AgNO3 → white ppt (1)

silver chloride (1)

1

NaNO3: Al + NaOH → pungent / sharp smell / choking gas (1)

NH3 / ammonia / turns (red) litmus blue(1)

1

Na2SO4: BaCl2 → white ppt (1)

barium sulfate (1)

1

each correct test and one result = 1 mark

one other result for any test = 1 mark this mark can only be awarded once

(ii) all would give a yellow / yellow-orange (flame) / same coloured (flame) / same results

allow orange (flame) 1

or

they all contain sodium

1

(b) any two from:

ignore cost/errors

• fast / quick or comment about speed

allow precise

• small amounts/sensitive

allow can be left to run/continuous analysis

• accurate

• ease of automation

accept operators do not need chemical skills

• sample not used up

• reliable / efficient

2

[7]

Q25.

(a) (i) any two from:

• bubbles / effervescence / fizzing

ignore hydrogen / gas produced

• lithium disappears / gets smaller

allow dissolves

do not allow melts / burns

• lithium moves on the surface of the water

ignore floats

• (universal indicator) turns blue / purple

2

(ii) 2

left-hand side correct

1

2

right-hand side correct

allow multiples for full credit

1

(iii) light / burn, which will give a (squeaky) pop / explosion

1

(iv) all have 1 electron in their outer shell / energy level

allow have the same number of electrons in their outer shell / energy level

1

(b) They react with oxygen

1

They have low melting points

1

(c) (i) electronic structure [2,8,8] is drawn

incomplete inner shells scores a maximum of 1 mark

1

charge is +

allow [2,8,8]+ for 1 mark

1

(ii) because (in potassium) the outer shell electron is further away from the nucleus or because potassium atoms are larger than sodium atoms

it should be clear that the candidate is referring to the outer shell electron: if this is not clear a maximum of 2 marks can be awarded

1

therefore the outer shell electron is less strongly attracted to the nucleus or is more shielded from the attraction of the nucleus and so the outer shell electron in potassium is more easily lost

1

3 marks can be scored for answering the question in terms of sodium

1

[13]

Q26.

(a) (i) magnesium oxide

1

(ii) decomposition

1

(b) (i) bar chart

1

(ii) more

1

(iii) limewater

1

turns cloudy / milky

accept forms a white precipitate

1

[6]

Q27.

(a) (i) yellow

1

(ii) lilac

1

(b) (bubble through) limewater

1

cloudy

allow white / milky

1

(c) (i) silver nitrate solution

1

(ii) white

1

[6]

Q28.

(a) (i) place sample in flame

accept flame test

accept any workable method

allow burn

ignore heat

1

sodium: yellow (flame)

allow orange

1

potassium: lilac (flame)

allow purple

1

(ii) (lilac) colour (of potassium) obscured by (yellow) colour of sodium

allow difficult to see two colours

allow sodium colour is brighter

allow colours mix

1

(b) acidify (with nitric acid)

do not accept if acidified with anything other than nitric acid

1

add silver nitrate (solution)

1

white precipitate

depends on second marking point

allow white solid

ignore silver chloride

ignore solution goes cloudy / milky

1

(c) (i) add excess (sodium hydroxide)

allow add sodium hydroxide

1

aluminium (ions / hydroxide (re)dissolve

depends on first marking point

allow if aluminium, (white) precipitate / solid dissolves

allow magnesium (ions / hydroxide) do not (re)dissolve

1

(ii) place sample in flame

accept flame test

accept any workable method

allow burn

ignore heat

1

flame does not go red

accept calcium (ions / hydroxide would produce) red flame

allow magnesium (ions / hydroxide) (produce) no flame colour

1

[11]

Q29.

(a) (i) fermentation

1

(ii) cloudy

accept milky / white

1

there is carbon dioxide / CO2

accept calcium carbonate forms

1

allow a (white) solid / precipitate forms

(b) (i) (the amount of ethanol used) increases (from 1970) to 1989

if no year(s) or incorrect year(s) indicated then max 1

correct year(s) only needs to be indicated once to gain full marks accept values in range 1987-1992

1

then it decreases from 1989 (to 2000)

1

(ii) any one from:

• Brazil had more oilfields

• cost of crude oil had decreased

• cost of ethanol / sugar (cane) had increased

• demand for ethanol / sugar (cane) had increased

• availability of ethanol / sugar (cane) had decreased

accept availability of land to grow sugar (cane) had decreased

• climate change affects growing sugar (cane)

1

[6]

Q30.

(a) limewater or calcium hydroxide solution

1

(reacts with carbon dioxide and) turns cloudy / milky

linked to first point

if no other mark awarded ‘puts out lighted splint’ gains 1 mark

1

(b) (i) any two from:

• same volume / amount of the acids

• concentration of the acids

• temperature

• same surface area / size / mass / amount of calcium carbonate

• same measuring equipment

2

(ii) any three from:

• (after about 4 minutes) the sulfuric acid stops reacting or nitric acid continues to react

accept more CO2 with nitric acid at any time after 4 minutes

• (initially) the reaction with sulfuric acid is faster

• (the reaction stops) because calcium sulfate is a solid

allow sulfuric acid produces a solid

• (the reaction continues) because calcium nitrate is soluble / in solution / aqueous

allow nitric acid produces an (aqueous) solution

• because the calcium sulfate prevents the sulfuric acid reacting with the calcium carbonate

• (the rate is faster) because sulfuric acid contains two hydrogens

3

[7]

Q31.

(a) (i) chromatography

1

(ii) 3 / three

1

(iii) the colour / E104 is not on the same level as any of the colours in the food

accept E104 does not match

1

(b) (i) to improve the appearance of the food

ignore adds yellow / colour

ignore taste / flavour

1

(ii) further / or different tests (for harmful effects) or obtain more evidence

(that it is harmful)

allow do a survey / study

1

[5]

Q32.

(a) (i) carbon dioxide / CO2

1

carbonate / CO32-

answers must be in the order shown

marks are independent

1

(ii) ammonia / NH3

1

litmus

answers must be in the order shown

marks are independent

1

(b) (i) solution is blue

accept blue precipitate only if sodium hydroxide added

allow blue liquid

allow copper sulfate / copper ions are blue

1

(ii) barium chloride / BaCl2

allow barium nitrate / barium ions / Ba2+

1

white

answers must be in the order shown

marks are independent

1

[7]