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Chemical changes - Reactivity of metals - Standard demand - Mark schemes

Q1.(a) An arrow indicating a position between aluminium and zinc.

1

(b) electrolysis1

because calcium is more reactive (than aluminium or carbon)accept it is more reactiveor very reactive

1

OR

in a blast furnace1

because calcium is less reactive (than carbon or lower)1

(c) any equation from1 mark for correct formulae1 mark for balancing

2ZnO + C → 2Zn + CO2

ZnO + CO → Zn + CO2

ZnO + C → Zn + CO1

[5]

Q2.(a) (test)

burning splint (held at open end of test tube)1

(result)a (squeaky) pop

1

(b)

Level 3: The design/plan would lead to the production of a valid outcome. All key steps are identified and logically sequenced.

5-6

Level 2: The design/plan would not necessarily lead to a valid outcome. Most steps are identified, but the plan is not fully logically sequenced.

3-4

Level 1: The design/plan would not lead to a 1-2

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valid outcome. Some relevant steps are identified, but links are not made clear.

No relevant content 0

Indicative content

• measure volume of hydrochloric acid

• in a measuring cylinder

• pour hydrochloric acid into suitable container

• measure temperature of hydrochloric acid

• using a thermometer

• measure mass of magnesium

• using a balance

• add magnesium to hydrochloric acid

• stir

• measure maximum temperature reached

• record maximum temperature reached

• calculate the change / rise in temperature

• repeat procedure for same mass of magnesium

• find mean temperature rise

• repeat with different masses of magnesium

6[8]

Q3.(a) any two from:

• copper / ores are running out / harder to find

• there are no / very small amounts of high-grade copper ores left

• copper metal is in demand

• copper is expensive

• now economical to extract copper from low-grade oresit = copperallow new methods of extraction e.g. bioleaching and phytominingallow high-grade ores are running out for 2 marks

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2

(b) (i) large amounts / 98% of rock to dispose of as wasteaccept contains toxic (metal) compounds / bioleacher

orwaste rock takes up a lot of space

1

(ii) (copper sulfide reacts with oxygen to) produce sulfur dioxide / SO2

allow (sulfur reacts with oxygen to) produce sulfur dioxide / SO2

1

that causes acid rainallow description of effects of acid rain or sulfur dioxideif no other mark awarded allow CO2 produced which causes global warming or CO2 produced by burning fuel or heating the furnace for 1 mark

1

(iii) any one from:

• large amounts of fuels / energy used (for the furnace and electrolysis)

allow large amounts of electricity neededignore high temperature / electrolysis unqualified

• (the extraction has) many steps / stages / processesallow (extraction) is a long process / takes a lot of time

• large amounts of ore / material have to be minedallow ores contain a low percentage of copper

1

(iv) (copper ions move towards) the negative electrode / cathode1

because copper ions / Cu2+ are positively charged or are oppositely charged or copper ions need to gain electrons

allow because metal ions are positive or opposites attract1

(v) (growing) plants1

[9]

Q4.(a)

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initial pH of hydrochloric acid is 0–31

pH increases as CuO is added1

horizontal from pH = 7 (from any mass of copper oxide)1

(b)

Level 2: The plan would lead to the production of a valid outcome. All key steps are identified and logically sequenced. 4-6

Level 1: The plan would not lead to a valid outcome. Some relevant steps are identified, but links are not made clear. 1-3

No relevant content 0

Indicative content

an ideal plan would be:

• use a rule to measure the length / use a balance to find the mass of the piece of magnesium

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• put magnesium into conical flask

• use measuring cylinder for dilute hydrochloric acid

• add dilute hydrochloric acid to conical flask

• connect bung (& delivery tube) into conical flask

• measuring cylinder is filled with water and inverted / upside down in bowl of water OR uses a gas syringe

• hydrogen flows through a delivery / rubber tube into measuring cylinder

• wait until all magnesium reacts / use excess dilute hydrochloric acid

• record volume when bubbles stop

other things they could mention:

• use accurate / 2 dp balance

• to collect gas use measuring cylinder / gas syringe with best resolution

• add bung quickly to ensure no gas escapes

• gas is collected in graduated apparatus (not test tube)

• repeat experiment (with same length / mass of magnesium)

• repeat at same temperature since volume of gas will be different

6

(c) (working)

data from candidate’s graph

1

(answer)0.8 (g of Cu per g of CuO)

1

(d) (working on graph)extension of straight line and finding y value when x = 7.5

1

factor of ×101

(answer) 60 (g)

or

(using gradient)y = 0.8 x

accept ecf from question part (c)

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0.8 × 75accept part (c) × 75

60

or

(stoichiometric method)

= 59.9 (g)1

[14]

Q5.(a) 408 kg

1

(b) all points correct± ½ small square

2

allow 1 mark if 5 points correct

best fit line1

(c) 1

5525 dm3

1

(d) relative formula mass of TiCl4 is 1901

25.26 %1

Answer given to 3 significant figures = 25.3 %1

25.23% with or without working gains 3 marks

(e) argon is unreactive1

water (vapour) would react with sodiumallow water (vapour) would react with titanium(IV) chloride

1

and air contains oxygen that would react with reactantsallow and air contains oxygen that would react with products

1

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(f) (titanium conducts electricity) because electrons in the outer shell of the metal atoms are delocalised

1

and so electrons are free to moveallow the delocalised electrons in the metal carry electrical charge through the metal

1

through the whole structure1

[15]

Q6.(a) (i) (thermal) decomposition

allow decomposes or endothermic1

(ii) copper oxide1

(b) (i) the (potassium) carbonate did not decompose/change/react (when heated)allow temperature not high enoughdo not allow potassium did not decomposeignore references to reactivity

1

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 or vice versa

needs to be a relative comparison2

allow max 1 mark where the distinction between a metal and its carbonate is not clearallow 1 mark for carbonates of reactive metals do not decompose or vice versa

(c) (i) make it economical (to extract the metal/iron)allow make it worth extracting allow so they can make money/profit

1

(ii) Fe1

balanced correctly (2,3,4,3)not ecfallow correct balanced equation but with 2Fe2 on right for one mark

1

(iii) iron from the blast furnace is brittle

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1steel produced is strong / flexible

allow steel has more/specific usesallow steel is rust-resistant

1

“it” = iron

(iv) (recycling) is used to conserve iron (ore) or energy or resources or minimise pollution or reduce the need to quarry

allow reverse arguments.1

(not reuse) because of damage, paint removal, rusting/corrosion, metal fatigue/weaker

1

(not landfill) because sites have limited space or loss of habitatsallow to reduce the use of landfill

1[15]

Q7.(a) any one from:

• solution becomes colourless or colour fades

• zinc becomes bronze / copper colouredallow copper (forms) or a solid (forms)

• zinc gets smallerallow zinc dissolves

• bubbles or fizzing.ignore precipitate

1

(b) improvement:use a plastic / polystyrene cup or add a lid

accept use lagging / insulation1

reason - must be linkedreduce / stop heat lossORimprovement:

use a digital thermometerallow use a data logger

reason - must be linked

more accurate or easy to read or stores dataallow more precise or more sensitiveignore more reliable

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ignore improvements to method, eg take more readings1

(c) 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 refer to the information in the Marking Guidance and apply a ‘best–fit’ approach to the marking.

0 marksNo relevant content

Level 1 (1−2 marks)There is a statement about the results.

Level 2 (3−4 marks)There are statements about the results. These statements may be linked or may include data.

Level 3 (5−6 marks)There are statements about the results with at least one link and an attempt at an explanation.

Examples of chemistry points made in the response:

Description:

Statements

Concentration of copper sulfate increases

Temperature change increases

There is an anomalous result

The temperature change levels off

Reaction is exothermic

Linked Statements

Temperature change increases as concentration of copper sulfate increases

The temperature change increases, and then remains constant

After experiment 7 the temperature change remains constant

Statements including data

The trend changes at experiment 7

Experiment 3 is anomalous

Attempted Explanation

Temperature change increases because rate increases

Temperature change levels off because the reaction is complete

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Explanation

As more copper sulfate reacts, more heat energy is given off

Once copper sulfate is in excess, no further heat energy produced6

[9]

Q8.(a) any three from:

• concentration of (salt) solution• volume of (salt) solution

ignore amount of solution• initial temperature (of the solution)

ignore room temperature• surface area / form of metal• moles of metal

allow mass / amountignore timeignore size of tube

3

(b) 201

321

12allow ecf

1

(c) (i) four bars of correct heighttolerance is + / - half square3 correct for 1 mark

2

bars labelled1

(ii) one variable is non-continuous / categoricaccept qualitative or discreteaccept no values between the metals

1

(iii) magnesium1

because biggest temperature changeaccept gives out most energyignore rate of reactiondependent on first mark

1

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(iv) does not react / silver cannot displace copper1

because silver not more reactive (than copper) or silver below copper in reactivity series

do not accept silver is less reactive than copper sulfate1

(v) replace the copper sulfatecould be implied

1

with any compound of a named metal less reactive than copperallow students to score even if use an insoluble salt

1[16]

Q9.(a) (i) any two from:

• bubbles / effervescence / fizzingignore hydrogen / gas produced

• lithium disappears / gets smallerallow dissolvesdo not allow melts / burns

• lithium moves on the surface of the waterignore floats

• (universal indicator) turns blue / purple2

(ii) 2left-hand side correct

1

2right-hand side correctallow multiples for full credit

1

(iii) light / burn, which will give a (squeaky) pop / explosion1

(iv) all have 1 electron in their outer shell / energy levelallow have the same number of electrons in their outer shell / energy level

1

(b) They react with oxygen1

They have low melting points1

(c) (i) electronic structure [2,8,8] is drawnincomplete inner shells scores a maximum of 1 mark

1

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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]

Q10.(a) (i) 2.8.3

any sensible symbol can be used to represent an electron1

(ii) proton(s) and neutron(s)both needed for the mark

1

(iii) number of protons is equal to number of electronsallow positive and negative charges cancel out allow same amount of protons and electrons

1

(b) (i) 2 Al + Fe2 O3 → 2 Fe + Al2 O3

equation must be balanced1

(ii) aluminium is more reactive (than iron)it = aluminiumaccept converseaccept aluminium displaces ironaccept aluminium is higher in the reactivity series (than iron)

1[5]

Q11.(a) (i) reduction

accept redox / smelting1

(ii) 3 4 31

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(b) (i) 55ignore other units

(ii) Wateraccept sodium hydroxideaccept correct formulae H2O or NaOH

1

(iii) any one from:

• save energy / fuel for transporting the oreaccept less (cost of) transport allow transported quickly

• (old) quarries nearby for waste/red mud1

(c) Environmental

any one from:

• less mining / quarrying (of bauxite)allow loss of habitat / less qualified noise pollution

• less landfill space needed / usedallow less red mud / waste

• less use of fossil fuels / energy

• less carbon dioxide produced1

Ethical or social

any one from:

• saves resourcesallow using resources more than once

• creates (local) employmentif answers reversed and both correct award 1 mark

• more people aware of the need for recyclingallow less qualified noise pollution if not given in environmental

1[7]

Q12.(a) any one from:

• no method / electrolysis / equipment / technologyallow ‘didn’t know how to’ or ‘no knowledge’

• aluminium is a very reactive metal

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• high melting pointallow ‘couldn’t heat it enough’

• potassium had not been discovered1

(b) because others / scientists / they could not repeat the experimentignore he could not repeat the experiment

orothers / they could not obtain the same results

1

(c) reaction is endothermic orreaction takes in heat / energy

accept activation energyignore rate / high temperatureignore bonds broken

1

(d) (aluminium chloride + potassium) → aluminium + potassium chloridein either orderaccept correct formulaeignore metalignore balancing

1

(e) when tested it had the properties of a metalaccept a test for a metal property eg conductivity / reaction with acid

1

properties were different (from other known metals)accept properties compared with other metals

1[6]

Q13.(a) (i) removal of oxygen

accept definition in terms of electrons or oxidation numbersignore oxides

1

(ii) 2 (Cl2)allow correct multiples

1

(iii) no atoms are lost / made (during a chemical reaction)orthe atoms are rearranged (during a chemical reaction)

accept because of (the law of) conservation of mass / matter1

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(b) (i) sodium is more reactive (than titanium)accept sodium is very reactive or titanium is less reactivedo not accept sodium is more reactive than argon

1

(ii) any one from:

• sodium / titanium would react with oxygen / airaccept air / oxygen is reactive

• sodium / titanium does not react with argonaccept argon is unreactive / inert / a noble gas / in group O

1

(c) (i) all atoms are the same / it only contains one type of atomaccept all ions are the samedo not accept only got one atomdo not accept all atoms are the same sizeignore particles

1

(ii) two different / types atoms / elements / ionsaccept more than one type of atom / ion / elementdo not accept different size

1

bonded / joined togetheraccept definite proportionsdo not accept mixture

1[8]

Q14.(a) (i) C

must be correct symboldo not accept carbonany balancing must be correct

1

(ii) Fe + CO2

correct formulae1

2... . + 3... .correct balancingallow Fe2 + 3CO2 for this mark

1

(iii) layers / atoms in pure iron are able to slide over each otherit = pure ironaccept ions for atomsignore molecules / particles

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or

layers / atoms in cast iron are unable to slide over each other (easily)1

(b) any three from:mention of ozone = max 2

• less iron ore usedaccept the idea that ores would be conserved but not unspecified conservation

• less other metals extracted / used to make different steelsaccept the idea that ores would be conserved but not unspecified conservation

• less fuel usedaccept the idea that fuels would be conservedignore reduces energy requirements

• less specified pollutionaccept global warming / greenhouse effect / CO2 / CO / carbon emissions / acid rain / SO2 / global dimming /do not accept ozone layer

• less / no landfill space neededignore reduces waste

• less / no mining needed or fewer specified effects of miningaccept effect such as eyesore / loss of habitateg ‘less mining iron ore’ = 2 marks

3[7]

Q15.(a) (i) contain enough metal to make it economical / worth while to extract

1

(ii) reductionaccept displacementaccept redox

1

(iii) Fe + CO2

do not accept Fe2 / Fe4

1

correct balancingaccept multiples and halves

2Fe2O3 + 3C → 4Fe + 3CO2

allow Fe2 / Fe4 as ecf1

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(b) Pure Iron

(in pure metal all the atoms are the same size and) able to slip / slide over eachother – (property soft)

OWTTEignore references to molecules / particlesif they say ‘move’ both times, allow one mark but ‘crack’ or ‘split’ is wrong..

1

Cast iron

(in cast iron) different sized atoms / larger atoms or structure is distorted / disruptedOWTTE

1

so it is difficult for layers of atoms to slip / slide over each otherOWTTE

1

(c) any three from:

• conserves / saves resources / metal ores

• saves energy resources (used for extraction / processing)accept cheaper / saves money

• decreases waste materials

• decreases a named pollutiondo not accept acid rain

3[10]

Q16.(a) (i) Cu2S + 2O2 ® 2CuO + SO2

accept fractions and multiple1

(ii) any two from:

• sulfur dioxide accept sulphur dioxide / sulphur oxide / SO2

• causes acid rain ignore other comments eg global warming / ozone / global dimming / greenhouse effect

• consequence of acid rain eg kills fish / plants2

(b) any two from:

• heat (copper oxide with carbon)

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• oxygen is removed by carbonaccept copper (oxide) loses oxygen

orcarbon gains oxygenaccept carbon oxide

or

carbon monoxide / carbon dioxide is produced

or

carbon displaces copperaccept a correct word or balancedsymbol equation

• because carbon is more reactive than copperallow a correct comparison of reactivity

2

(c) (i) electrolysisaccept electroplating

1

(ii) (electrical) wiring / appliances / coins / pipes / cladding forbuildings / jewellery / making alloys

1

or

named alloys

(d) any three explanations from:

for recycling

• less acid rain (pollution)

• copper reserves last longer / conserved

or

do not run out

• energy for extraction (saved)

or

less energy required

• less mining / quarrying

• less waste (copper) / electrical appliances dumped

or

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less landfill

against recycling

• collection problems

• transport problems

• difficult to separate copper from appliances

• energy used to melt the collected copperignore electrolysis / pollutionignore ideas about less machinery / plantignore idea of cost

3[10]

Q17.(a) (i) 5(%)

1

(ii) 0.35

for 1 mark

2

(b) (i) reductionaccept (it’s) reduceddo not accept redox / deoxidation

1

(ii) heat with / reduce / react with or (chemical) reaction1

with a metal / element / substance higher in reactivityignore displaceaccept higher named elements or symbolaccept carbon monoxide / coal / cokecorrect word equation for 2 markscorrect formulas for 1 markcorrect balanced symbol equation for 2 marks

1

or

electrolysis:molten (1)electrolysis (1)

[6]

Q18.

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(a) (very) small percentage / amount (in the Earth’s crust)any indication that there is a smallamount, eg not much (left)accept rare (elements) / rareraccept not commonly foundignore cannot find easilyignore hard to extract

1

(b) (i) oxygen / O / O

do not accept O1

(ii) any one from:

• potassium / K• sodium / Na• calcium / Ca• magnesium / Mg

symbols must be correctwrite name and incorrect symbol, ignore symbol

1

(c) (i) heating (with) or hot air blown into furnaceaccept high temperatures or (very) hot

1

carbon / carbon monoxide / coke / coking coaldo not accept coal / charcoal accept balanced equation only

orcarbon reacts with O2 or carbon / coke burning (1)

accept balanced equation only CO / CO2

CO reacts with the ore (1)for naming the reducing agent

1

(ii) cost of melting ore / electricitymakes aluminium expensive (owtte)or (large amount of) electricity usedor because you have to use electrolysisor aluminium is higher in the reactivity seriesor aluminium is harder to reduceor unable to reduce with carbonor the cost of purifying the bauxite

do not accept harder to extract / producemore energy is not enough

1[6]

Q19.(a) Zn + 2HC 1 → ZnC12 + H2

1

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(b) (i) 12.51

(ii) steeper curve same volume of gas evolveddo not credit two intersects of straight linesaccept a sharp bend

2

(iii) any two from:

stir itaccept mix it better

heat itaccept warm it

use a more finely divided catalystaccept use a better catalyst or more finely divided zincdo not credit use acid of a higher

2

(c) (i) any one from

zinc is more reactive than copperaccept zinc is above copper in the reactivity series

zinc displaces copperaccept it is higher than copper in the reactivity series

1

(ii) zinc + copper sulphate → copper + zinc sulphateignore the presence of acid or wateraccept a balanced equation

1[8]

Q20.(a) gives out

heateach for 1 mark

2

(b) chromium and aluminium oxide1

(c) (i) chromium oxide1

(ii) oxygen removed/gains electrons1

[5]

Q21.

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(i) idea that:carbon is above lead in the reactivity series } NOT

for 1 mark

carbon is below aluminium in the reactivity series } OXIDEfor 1 mark

carbon can remove oxygen from/reduce lead oxide or cannot remove oxygen from aluminium oxidenot aluminium more reactive than lead

for 1 mark

OR similar ideas in comparing bond strengths3

(ii) (carbon + lead oxide) →*lead + *carbon dioxideeach for 1 mark

accept correct formulae CO2 and CO NOT carbon oxide2

[5]

Q22.correct use of ‘react’/‘reaction’/reactants’/combine(not mixed/added/join)correct use of ‘produce’/‘products’/gives/forms/makes/createsreactants correctly identified

each for 1 mark

products correctly identified(Reactants must be correctly identified for ‘react’mark to be awarded. Similarly for products)(magnesium reacts with zinc oxide to produce magnesiumoxide and zinc or similar, will gain all 4 marks)Oxidise or reduce given correctly can be credited both the marks for react and produce

[4]

Q23.(a) ideas that it is a

• compound of metal/metal oxide/combined (NOT mixed) cpd/named cpd O2-/S2-/CO3

2- etc

• found naturally/in rocks/in Earth’s Crustfor 1 mark each

2

(b) reduction (accept smelting/refining but not electrolysis) for 1 mark

1

(c) One example. Al or above in Reactivity Seriesie Group I or II metals NOT Pb/Cu or compounds

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for 1 mark1

[4]

Q24.(a) (i) gold is unreactive

1

(ii) 2Fe2O3 + 3C → 4Fe + 3CO2

products may be in either order1 mark for correct symbols1 mark for correct balancingallow correct multiples

2

(iii) aluminium is high in the reactivity seriesoraluminium is more reactive than carbon

allow aluminium is very reactive1

(so) cannot be extracted with carbonor(so) requires electrolysis

allow electrolysis is required (1 mark)(but) electricity / technology not available (1 mark)

1

(b) lower density and higher strength1

[6]

Q25.(a) rare

or

very small amount in Earth’s crustignore figures without qualification

1

(b) (i) electrolysis1

(ii) (electrolysis) uses more energy

or

there are many stages in the processignore references to reactivityaccept uses a large amount of energy

1[3]

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Q26.(a) rare

or

very small amount in Earth’s crustignore figures without qualification

1

(b) (i) electrolysis1

(ii) (electrolysis) uses more energy

or

there are many stages in the processignore references to reactivityaccept uses a large amount of energy

1

(c) 2Fe2O3 + 3C → 4Fe + 3CO2

correct formulae for 1 markcorrect balancing of correct formulae for 1 markallow multiplesaccept for 2 marks:Fe2O3 + 3CO → 2Fe + 3CO2

2[5]

Q27.(a) oxygen / O2 / O

1

(b) (i) zinc boils / evaporates out of furnace becauseof its low boiling point

1

therefore because lead has a high boiling pointit remains in the furnace

1

(ii) on cooling the zinc forms a solid and the lead remains liquidaccept because zinc is less dense it floats on lead

1

therefore the lead can be poured off / decanted from the zincaccept therefore the zinc can be poured off / decanted from the lead

1[5]

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