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Transition Metals, Alloys &

Corrosion Mark Scheme 1

Level Edexcel

Subject Chemistry

Exam Board GCSE(9-1)

Topic Separate Chemistry 1

Sub Topic Transition Metals, Alloys & Corrosion

Booklet Mark Scheme 1

Time Allowed: 56 minutes

Score: /46

Percentage: /100


Question Number

Answer Acceptable answers Mark

1(a) B potassium and caesium, copper and iron

(1)

Question Number


1(b)(i) A description linking

(regular arrangement of) positive ions /cations (1)

(surrounded by) {delocalised/sea of} electrons (1)

Any reference to molecules/molecular/intermolecular/covalent scores 0 marks overall

metal ions

reject “negative and positive particles” / positive atoms / protons

ignore descriptions of atoms in rows/ layers of particles etc

cloud of electrons ignore free

(2)

Question Number


1(b)(ii) An explanation linking

M1 electrons (1)

M2 move/flow (1)

M2 dep on M1

pass through / travel

For M2: ignore free/delocalised (electrons) ignore electricity flows ignore (electrons) vibrate ignore carry/pass the current/charge (2)


Question Number


1(c)(i) A description including any two from

floats (1)

moves (around) (1)

effervescence / fizzing / bubbles (1)

melts/changes to a ball shape (1)

becomes smaller /disappears (1)

moves (around) on the surface (2)

white smoke formed ignore gas/hydrogen given off

dissolves / explodes Ignore: burns/catches fire/ignites/flame/sparks ignore addition of indicators

(2)

Question Number


1(c)(ii) 2Na + 2H2O → 2NaOH + H2

LHS (1) RHS (1) balancing of correct formulae(1)

NaHO

ignore brackets around OH

Use of lower case h, upper case A, lower case o, or use of superscripts or large numbers inside the formulae loses 1 mark only

ignore state symbols (3)


Question Number


2(a) An explanation including two of

• does not corrode/tarnish(1)1)

• unreactive (1) M2

• shiny/lustrous (1) M3• malleable/easily shaped

(1)1)• scarce/expensive/maintain

s its value (1) M5

Ignore does not rust

does not react with oxygen and/or water Ignore least reactive/less reactive/not very reactive/reacts very slowly

attractive Ignore soft/strong

valuable

(2)

Question Number


2(b) C 24 carat (1)

Question Number


2(c) An explanation linking three of

• (gold) atoms all same size(1)1)

• {layers/sheets} (of atoms){slide/slip/move} M2(over one another easily)(1)

• (alloy) added metalsatoms are different size(1)1)

• disrupt{layers/structure/arrangement} of goldatoms (1) M4

• prevent {layers/atoms}{slide/slip/move} (1) M5

Marks can be gained from suitable diagrams No mention of layers/sheets in answer maximum 2 marks

Accept particles/ions for atoms reject molecules (once only)

{lock/hold} layers/atoms together

(3)


Question Number

Indicative Content Mark

QWCQWC *2(d) An explanation including some of the following points

reactivity series

• aluminium more reactive than iron/aluminium higherthan iron in reactivity series

• aluminium forms stronger bonds with oxygen than irondoes

• aluminium oxide more stable (to decomposition) thaniron oxide

• aluminium more reactive than carbon/aluminium higherthan carbon in reactivity series

cost

• electrolysis/electricity (more) expensive (than heatingwith carbon)

• heating with carbon is (relatively) cheap method

Iron

• carbon more reactive than iron/iron less reactive thancarbon

• iron oxide reduced• by heating with carbon• no need to use (expensive) electrolysis•

Aluminium • aluminium oxide difficult to reduce• aluminium oxide cannot be reduced by (heating with)

carbon• (cheaper) reduction with carbon does not work• need more powerful method of reduction• therefore must use electrolysis

(6)

Level 0 No rewardable content 1 1 - 2 • a limited description e.g. aluminium is very reactive

e.g. aluminium extracted by electrolysise.g. iron extracted using carbone.g. costs more to extract aluminium

• the answer communicates ideas using simple language and useslimited scientific terminology

• spelling, punctuation and grammar are used with limitedaccuracy


2 3 - 4 • a simple description containing two statements referring to onemethod of extraction and a cost e.g. iron is extracted by heatingiron oxide with carbon and this is cheaper

OR the relative reactivity of one metal and a method ofextraction e.g. aluminium is extracted by electrolysis. Aluminiumis more reactive than iron (has made a comparison in reactivity)

OR the relative reactivity of one metal and reference to coste.g. aluminium is a more reactive metal and so is expensive toextract

• the answer communicates ideas showing some evidence of clarityandorganisation and uses scientific terminology appropriately

• spelling, punctuation and grammar are used with some accuracy3 5 - 6 • a detailed description containing at least three statements

referring to relative reactivity of both metals, a method ofextraction of at least one metal, and a cost reference

e.g. aluminium is more reactive than iron so is extracted byelectrolysis which is expensive

• the answer communicates ideas clearly and coherently uses arange of scientific terminology accurately

• spelling, punctuation and grammar are used with few errors


Question Number


3(a) C (1)

Question Number


3(b) a description including the following

• heat/reduced {with} (1)

• (with) carbon/coke/carbonmonoxide(1)

Ignore references to blast furnace

Reject references to electrolysis (2)

Question Number


3 (c) A description including three of the following, with a maximum of two from either group of three

OR

• reduction is the loss ofoxygen (1)

• copper(oxide) losesoxygen (1)

• (hence) copper (oxide) isreduced (1)

• oxidation is the gain ofoxygen (1)

• hydrogen gains oxygen (1)

• (hence) hydrogen isoxidised (1) (3)


Question Number


3(d) an explanation linking one of the following pairs

OR

• when bent / deformed (1)• shape memory alloys

return to their originalshape (1)

• shape memory alloysreturn to their originalshape (1)

• (but) other alloys staydeformed (1)

must refer to metal’s shape being changed i.e. ignore “broke”, “sat on etc.”

(2)

Question Number


3 (e) C (1)


Question Number


4(a)(i) Any one from

• steel {corrodes/rusts}

• prevents {corrosion/rusting}

• (copper) does not{corrode/rust}

• (copper) oxidises slower

• kills bacteria (1)

copper is less reactive than {iron/steel}

does not oxidise/does not react with {oxygen/water} prevents germs spreading

cheaper than (using) pure copper

Ignore to make it less reactive and references to appearance and erosion (1)

Question Number


4(a)(ii) zinc Zn (1)

Question Number


4(b) An explanation linking three of the following:

• in pure metal{layers/sheets} (ofparticles){slide/slip/move}(over one another easily) (1)

• second (metal) particleslarger (1)

• disrupt {layers/structure}(1)

• prevent {layers/particles}slipping (1)

Accept ions or atoms for particles but reject molecules

different sized particles

{lock/hold} layers together Ignore glue

(3)


Question Number


4(c)(i) D (1)

Question Number


4(c)(ii) An explanation linking two of the following

• (aluminium) more reactive (1)

• forms more stable compounds(1)

• more difficult {to removeoxygen /split (compound)} (1)

• electrolysis is more powerfulmethod of reduction (1)

too reactive/{above carbon/higher up} in reactivity series forms compounds with stronger bonds

carbon {cannot remove oxygen/displace aluminium}

(2)


Question number

Answer Mark

5(a)(i) C (1)

Question number

Answer Mark

5(a)(ii) C (1)

Question number

Answer Mark

5(b) reactants are being used up (1) (1)

Question number

Answer Mark

5(c) An explanation that combines identification via a judgement (1 mark) to reach a conclusion via justification/reasoning (1 mark): • aluminium and copper have different size atoms (1)• and so this prevents the layers of metal atoms from sliding

over one another (1) (2)

Question number

Answer Additional guidance Mark

5(d) proportion gold = 9 ÷ 24 (= 0.375) (1)

mass = 0.375 × 12 = 4.5 (g) (1)

Award full marks for correct numerical answer without working.

(2)


Transition Metals, Alloys &

Corrosion Mark Scheme 2

Level Edexcel

Subject Chemistry



Sub Topic Transition Metals, Alloys & Corrosion



Score: /51

Percentage: /100


Question Number


1(a)(i) C cations in a sea of electrons (1)

Question Number


1(a)(ii) (metals have) high melting point a lot of energy needed to break/overcome (metallic) bonds

energy needed to break/overcome strong (metallic) bonds

Ignore references to boiling point Reject reference to intermolecular forces/covalent (bonds) /attraction between ions/breaking ionic bonds/ breaking covalent bonds

(1)

Question Number


1(a)(iii) An explanation including two of the following points

• argon is inert/does notreact/is unreactive (1)

• because it has 8 electrons inits outer shell (1)

• metals would react in/withair/oxygen (1)

• argon will exclude air fromwelding point (1)

Ignore argon is in group 0/8 argon is a noble gas Ignore argon does not burn

does not {gain/lose/share} electrons

has a full outer shell (of electrons)

has a stable electron configuration

form (metal) oxide

prevents oxidation (2)


Question Number


1(b) 2 Fe + 3 Br2 → 2 FeBr3

M1 Correct symbol/formulae (1) M2 balancing of correct symbol/formulae (1)

Reject incorrect use of upper/lower case / subscripts for M1 but allow ECF for M2 (2)

Question Number


1(c) C – grey solid

(1)

Question Number


1(d) A explanation including

M1 order of reactivity chlorine > bromine > iodine (1)

and M2 one of the following points

• chlorine displaces bromine(from bromide) AND chlorinedisplaces iodine (from iodide)(1)

• bromine displaces iodine(from iodide) AND brominedoes not displace chlorine(from chloride) (1)

• iodine does not displacechlorine(from chloride) ANDiodine does not displacebromine (from bromide) (1)

For M1 reject reference to reactivity of halide ions eg chlorine more reactive than bromide

halogens/they decrease in reactivity down the group/table

chlorine is most reactive and iodine is least reactive

Ignore reference to displacement of halide ions eg chlorine displaces bromide

Ignore “replaces”

chlorine reacts with bromide AND iodide chlorine takes part in two (displacement) reactions

bromine reacts with iodide AND does not react with chloride bromine takes part in one (displacement) reactions

iodine does not react with chloride or bromide iodine does not take part in any (displacement) reactions

(2)


Question Number


2(a) C oxygen other gases nitrogen (1)

Question Number


2(b)(i) A description to include

Photosynthesis /absorbcarbon dioxide andreleases oxygen (1)

(green) plants (1)

reject respiration for photosynthesis

ignore breathe in carbon dioxide ignore breathe out oxygen

(2)

Question Number


2(b)(ii) A description to include

second marking is dependent on the first

a glowing splint (1)

relights (1)

smouldering splint reject a blown out splint

lit splint glows brighter (2) (2)

Question Number


2(c)(i) to ensure all the oxygen is removed/to ensure the oxygen is completely removed

ignore ensure all the air is removed

(1)


Question Number


2(c)(ii) An explanation linking

measure the volume of gasin the syringe at the end ofexperiment (1)

subtract from {100 cm3 /original volume} to givevolume of oxygen (1)

e.g. 100-79 (= 21 cm3)

(2)


Question Number


3(a) loss of oxygen gain of electrons (1)

Question

Number


3(b) An explanation to include

aluminium high in reactivityseries / aluminium more

reactive than {carbon / iron}(1)

(aluminium reduction) needsmore energy / electrolysis is

{more / very} powerful(means of reduction) / carbon

cannot displace aluminium(from aluminium oxide) (1)

aluminium compounds are stable aluminium is more reactive

ignore just ‘very reactive’/highly reactive

allow stronger (method of reduction)

(2)

Question Number


3(c) 2Fe2O3 + 3C 4Fe + 3CO2 (3)

lhs (1) rhs (1) balancing correct formulae (1)

(3)


Question

Number


QWC *3(d) A description including some of the following points

Property change (other than increased strength) or use of alloy

increased hardness decreased malleability

increased corrosion resistance shape-memory gold alloy for jewellery

stainless steel used for cutlery steel used for construction

nitinol (shape-memory alloy) used for spectacle frames /stents

idea of any use of metal after alloying

Structural change

pure metal – atoms are all the same size / suitable diagramof pure metal structure

atoms arranged in a regular way / lattice

alloy – atoms are of different sizes / suitable diagram ofalloy structure

disrupts arrangement of atoms atoms in pure metal structure can slide over each (when

bent)

alloy – sliding prevented by different sized atoms

(6)


Level 0 No rewardable content

1 1 – 2 a limited description of how one property changes, one use or

one statement related to structure eg iron rusts, stainless steeldoes not; atoms in a pure metal all the same size

the answer communicates ideas using simple language and uses

limited scientific terminology spelling, punctuation and grammar are used with limited

accuracy

2 3 – 4 a simple description of how two properties change or two uses or

a simple description of why alloys become stronger or aproperty/use and a statement about structure eg the atoms in apure metal have a regular arrangement but in alloys there are

different sized atoms the answer communicates ideas showing some evidence of

clarity and organisation and uses scientific terminologyappropriately

spelling, punctuation and grammar are used with some accuracy

3 5 – 6 a detailed description of why alloys become stronger including atleast one change in property of an alloy or use eg the atoms in a

pure metal have a regular arrangement but in alloys the differentsized atoms stops the atoms sliding over each other and how

alloys are more useful such as gold alloys used in jewellery the answer communicates ideas clearly and coherently uses a

range of scientific terminology accurately

spelling, punctuation and grammar are used with few errors


Question Number


4(a)(i) carbon (is oxidised) Just ‘carbon dioxide’ (0) (1)

Question Number


4(a)(ii)(a)(ii) 1 mark if answer only mentions one of the metals.

An explanation linking two of

iron is lower in reactivity than aluminium/ORA (1)

carbon can remove the oxygen from iron oxide (1)

electrolysis is a more powerful method (than using carbon) / electrolysis is needed to {remove the oxygen from/reduce} aluminium oxide (1)

iron compounds less stable than aluminium compounds/ORA (1)

Allow carbon is more reactive than iron /ORA(1)

Allow aluminium is more reactive than carbon /ORA (1)

Ignore carbon can reduce iron oxide

Ignore electrolysis is used to extract aluminium

(2)


Question Number


4(b) An explanation linking three of

atoms of gold all the same (size) (1)

in pure gold {layers/rows/sheets/lines} of the {gold / metal} atoms slide over each other (when force is applied) (1)

copper atoms are {smaller / different size} (1)

(copper atoms) {disrupt / distort /disturb} the {structure / layers} (1)

stops {layers/rows/sheets/lines} of gold atoms from sliding over each other (1)

Reject the use of the word molecule once only

Allow particles

If layers/rows/sheets/lines is omitted twice, you can award one mark.

(3)


Question Number


QWCQWC *4(c) An explanation including some of the following points Usese Relevant properties

Aluminium aeroplanes, cars, bicycles, trains, trucks, ladders, window frames, door frames, greenhouses, pylons, ship masts, walking poles, golf clubs, baseball bats

low density (allow light), strong, resistant to corrosion

(overhead) power/electricity cables

low density (allow light), good conductor of electricity, resistant to corrosion

foil, food packaging, cans, sweet wrappers, saucepans, blister packs for pills

low density (allow light), resistant to corrosion

Copper electrical wires/cables, lightning conductors, electromagnets

good conductor of electricity

water pipes, roofing, coins, jewellery, statues, musical instruments

resistant to corrosion

Gold jewellery, coins, in dentistry excellent resistance to

corrosion, valuable, low strength

electronic devices, circuit boards, switch contacts

excellent conductor of electricity

Silver jewellery, cutlery, coins very good resistance to

corrosion, valuable, low strength

electronic devices, circuit boards, switch contacts

excellent conductor of electricity

General points A property must be relevant to the use and from the table in the question. Ignore additional properties. Look for the use first, then the relevant property. Candidates who just re-write or compare the properties with no uses score no marks. Ignore non-specific uses such as building materials/structures, making alloys

(6)


0 Level No rewardable content 1 -

2 1 a limited explanation e.g. states correct uses of two metals / explains a

use of one of the metals related to a property in the table the answer communicates ideas using simple language and uses limited scientific terminology spelling, punctuation and grammar are used with limited accuracy

2 -4 3 a simple explanation e.g. states correct uses of three metals and relates

one use to a property / explains uses of two metals related to their properties in the table the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately spelling, punctuation and grammar are used with some accuracy

3 -6 5 a detailed explanation e.g. explains uses of three metals and relates use

to property in the table in each case the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, punctuation and grammar are used with few errors


Question Number


5(a)(i) CuCl2 (1)

Question Number


5(a)(ii) An explanation linking the following points Either

Or

• the amount of productcalculated (1)

• using the equation (for thereaction) (1)

• the maximum amount of{product / copper chloride}(1)

• when all {reactant / copper}reacts (1)

using reacting masses

amount of product when all {reactant / copper} reacts (2)

(2)

Question Number


5(b)(i) 2Fe(s) + 3Br2(g) → 2FeBr3(s)

reactant formulae (1) balancing correct formulae (1) state symbols (1)

s and g must be lower case

allow state symbol mark even if other marks not awarded (3)

Question Number


5(b)(ii) 56 + (3 x 80) (1) = 296

give full marks for correct answer with no working (1)

Question Number


5(b)(iii) ratio: 56/310 (1)

% iron 56/310 x 100 (%) (1)

(= 18 (%))

any number/310 x 100 (%)

18.06/18.1 give full marks for correct answer with no working

(2)


Question Number


5(b)(iv) HO OH,O1H1,H1O1 (1)


Quantitative Analysis Mark Scheme 1

Level Edexcel

Subject Chemistry



Sub Topic Quantitative Analysis



Score: /45

Percentage: /100


Question Number


1(a) (=111)

(= 0.1)

(=0.2)

CaCl2 = 40 + 35.5 + 35.5 (1)

THEN moles = 11.1 / 111

(1) conc = moles x 1000/500 (1)

OR

(=22.2)

(= 0.2)

mass conc = 11.1 x 1000/500 (1) conc = mass conc/111

(1)

0.2 scores 3

ecf: 11.1 / Mr

ecf: mass conc / 111

(3)

Question

Number


1(b)(i) A description linking

pipette (1) one practical point eg draw

liquid up to line/ usepipette filler/ rinse first /read at eye level (1)

ignore burette etc for 1st mpt if using measuring cylinder/

burette allow suitable practical point eg read at eye level/ add dropwise from burette near 25

cm3 (1) ignore as 2nd point: transfer

liquid to flask / safety precautions

(2)

Question

Number


1(b)(ii) D 25.20 cm3 (1)


Question

Number


QWC *1(c) A description / explanation including some of the following points

soft

add soap (solution) shake/ mix lather (immediately)

no scum/ no precipitate

permanent hard add soap (solution) shake

no lather / less than with soft water scum/ precipitate

boiled sample same results / boiling does not change becomes soft after ion exchange but not after boiling

temporary hard

add soap (solution) shake no lather / less than with soft water

scum/ precipitate boiled sample

after boiling precipitate / (lime)scale formed lather (immediately)

credit quantitative approaches e.g. titration with soap solution

(6)


Level 0 No rewardable content

1 1 - 2 a limited description e.g. test and one result / when shaken withsoap, soft water makes lather but no scum

the answer communicates ideas using simple language and useslimited scientific terminology

spelling, punctuation and grammar are used with limited accuracy

2 3 - 4 a simple description e.g. describe test and results to distinguishthe soft water and the two samples that are hard water / when

shaken with a small amount of soap, soft water makes a latherand no scum but the other waters make scum but no (less) lather

the answer communicates ideas showing some evidence of clarityand organisation and uses scientific terminology appropriately

spelling, punctuation and grammar are used with some accuracy

3 5 - 6 a detailed description e.g. describe test and results to identify all

three of the samples / as 3-4 and boil the two hard water samplesand repeat test. That which now gives a lather is temporarily hard

the answer communicates ideas clearly and coherently uses a

range of scientific terminology accurately spelling, punctuation and grammar are used with few errors


Question Number


2(a) A neutralisation (1)

Question Number


2(b) Any one from

• no {sharp/clear/distinct}change in colour

• gradual colour change

• there are too many differentcolours

ignore not as accurate/reliable

allow too difficult to see when it is {neutral/reaction is complete}

ignore speed of colour change

(1)


Question Number


QWCQWC *2(c) A description including some of the following points

titration experiment • rinse pipette with alkali and burette with acid• measure alkali using a pipette• into suitable container e.g. flask/beaker• add a few drops of indicator / suitable named indicator (eg

methyl orange/phenolphthalein)• flask on a white tile• fill burette with acid• read level/volume (of acid) in burette• add acid from burette to the flask slowly / swirl the flask• until {indicator just changes colour/correct colour change for

named indicator (eg methyl orange yellow to peach/orange,phenolphthalein pink to colourless)/solution is neutral}

• read level/volume (of acid) in burette• repeat experiment• until concordant results

salt preparation • mix the same volume of alkali with the volume of acid

determined from the first experiment but do not addindicator (or add (activated) charcoal to remove indicator,then filter)

• pour solution into an evaporating basin• {heat solution/leave the water to evaporate} until pure salt

crystals are left (6)

0 Level No rewardable content 1 1 - 2 • a limited description of titration and/or salt preparation e.g. add

hydrochloric acid to sodium hydroxide solution in a flask, thenevaporate the water from solution.

• the answer communicates ideas using simple language and useslimited scientific terminology

• spelling, punctuation and grammar are used with limited accuracy2 3 - 4 • a simple description of titration and/or salt preparation e.g. pipette

sodium hydroxide solution into flask, add indicator, place hydrochloricacid in burette, add acid to alkali until colour change.

• the answer communicates ideas showing some evidence of clarity andorganisation and uses scientific terminology appropriately

• spelling, punctuation and grammar are used with some accuracy3 5 - 6 • a detailed description including titration and salt preparation e.g.

pipette sodium hydroxide solution into flask, add indicator,hydrochloric acid in burette, add acid to alkali until colour change,repeat until concordant results, evaporate water.

• the answer communicates ideas clearly and coherently uses a rangeof scientific terminology accurately

• spelling, punctuation and grammar are used with few errors


Question Number


2(d)(i) 22.6 + 22.8 2 (1) (= 22.7)

(1)

Question Number


2(d)(ii) marks are for the working

no. moles HCl = 23.2 x 0.1 (1) 1000

( = 2.32 x 10-3)

no. moles NaOH = no. moles HCl (1)

conc NaOH = 2.32 x 10-3 x 1000 (1)

25.0 ( = 0.0928 mol dm-3)

mark consequentially OR no. moles NaOH reacting = 1 (1)

1 no. moles HCl reacting

25.0 x conc = 1 (1) 23.2 x 0.1 1

conc NaOH = 0.1 x 23.2 (1) 25.0

(= 0.0928) mol dm-3

OR use of c1v1 = c2v2 (1)

0.1 x 23.2 = conc x 25.0 (1)

conc NaOH = 0.1 x 23.2 (1) 25.0

(= 0.0928) mol dm-3

0.0928/0.093 with or without working (3)

0.09 with no working (2)

common incorrect answers with working

0.108/0.1077 (2) – used 1:1 ratio but 25x0.1/23.2

0.928 (2) – used 1:1 ratio but missed out 0.1

(3)


Question number


3(a) Formula mass ammonium chloride = 14.0 + 4.00 + 35.5 = 53.5

moles of ammonium chloride 10.0

= = 0.187 (1) 53.5

volume ammonia = 0.187 × 24 = 4.49  dm3 (1) or • 2 × 53.5 = 107  g ammonium

chloride produces 2 × 24 =48  dm3 ammonia (1)

• 10.0  g ammonium chlorideproduces

2×53.510.0 × 2 × 24 = 4.49  dm3

ammonia (1)


(2)

Question number


3(b)(i) 25 ÷ 1000 × 0.1 = 0.0025 (1)

35 ÷ 1000 × 0.075 = 0.002  625 (1)

The acid is in excess (1) Third mark only awarded as conclusion from calculated data. (3)

Question number

Answer Mark

3(b)(ii) 36.20 + 36.302

= 36.25 (1) (1)

Question number

Answer Mark

3(b)(iii) D (1)


Question number


3(c) mol of acid = 24.80 ÷ 1000 × 0.200 (= 0.004  96 mol) (1)

mol NaOH = 2 × 0.004  96 (= 0.009  92) (1)

conc. of NaOH = 0.009  92 ÷ 25.0 × 1000 (1)

= 0.3968/0.397 (mol dm-3) (1)

or

(25.00 × conc NaOH) ÷ 2 = 24.80 × 0.200 (2)

conc NaOH = 2 × 24.80 × 0.200 ÷ 25.00 (1)

= 0.3968/0.397 (mol dm-3) (1)


Allow max 3 marks if missing ‘2 ×’ in step 2.

(4)


Question Number


4(a) D aq l (1)

Question Number

Answer acceptable answers Mark

4(b) H+ + OH- (1) H2O (1) LHS (1) RHS (1) ignore state symbols, even if incorrect. allow inclusion of spectator ions, Na+ and Cl-, if shown on both sides for one mark max

(2)

Question Number


4(c)(i) suitable acid-base indicator eg methyl orange, phenolphthalein

litmus reject universal indicator allow recognisable phonetic spelling

(1)

Question Number


4(c)(ii) correct colour change for suitable indicator in 4(c)(i):

methyl orange : yellow orange/pink/red

phenolphthalein : magenta/pink colourless

litmus : blue red

ignore clear (1)

Link 4ci and 4cii together on e-Pen

Question Number


4(d) rel mass NaOH = 23.0 + 16.0 + 1.00 (1)

concentration = 20.0 x 1 (1) formula mass

(= 40.0) (1)

0.5 (mol dm-3) without working (2) (2)


Question Number


4(e) moles of NaOH = 25.0 x 1.50 (1) 1000

(= 0.0375 moles) ratio 1 : 1 / moles NaOH = moles HCl (1)

conc of HCl = 0.0375 x1000 (1) 30.0

(= 1.25 (mol dm-3)) OR 25.0 x 1.50 = 30.0 x conc acid (2)

conc of HCl = 25.0 x 1.50 (1) 30.0 (=1.25 (mol dm-3))

0.0375 (1) – without working shown

conc of HCl = 1.25 (mol dm-3)(3) without any working shown allow ecf

conc = 30.0 x 1.50 = 1.80 (2) 25.0 (mol dm-3)

allow 0.00125 /0.125 / 12.5 max 2

(3)


Quantitative Analysis Mark Scheme 2

Level Edexcel

Subject Chemistry



Sub Topic Quantitative Analysis



Score: /19

Percentage: /100


Question Number


1(a)(ii) (carbon dioxide) dissolved/ absorbed / trapped

Ignore refs to plants/ rocks (1)

Question Number


1(a)(iii) A description including the following points

• (primitive) plants (produceoxygen) (1)

• (by) photosynthesis (1)

Allow named plants

Reject answers involving respiration

(2)

Question Number


1(b)(i) C (1)

Question Number


1(a)(i) {water vapour / steam} condensed/ changed to liquid

Allow steam cooled (1)

Question Number


1(b)(ii) all oxygen {reacted / used up} / excess copper (present)

no oxygen left / insufficient oxygen

Reject not enough time / not hot enough (1)


Question Number


1(b)(iii) volume gas used = 32-24 (1) = 8 (cm3)

percentage = 32-24/32 x 100 (1) = 25 (%) (2)

Question Number


1(b)(iv) oxygen in air in test tube also reacted /more than 32 cm3 of air because of air in test tube / air in test tube will react but is not measured

some gases leaked out of apparatus

allow another gas has reacted with copper (1)


Question Number


2(a) A description including:

• add (dilute) (hydrochloric) acid(1)

• gas/carbon dioxide (passedinto/tested) with limewater (1)

• limewater goes milky / cloudy /white ppt (1)

correct formulae

heat/thermally decompose

bubbled through limewater

dependent on use of limewater (3)

Question Number


2(b) 40 +[2 x 35.5] (=111) 111 alone (1)

Question Number


2(c) • 100 (kg) (calcium carbonate) 106 (kg) (sodium carbonate)

(1)

• 106x40 (1) (=42.4) 100

OR alternative 106÷100 40000÷100 /40÷100 (moles approach)

Only 42.4 with no working worth 2 marks 42400g worth 2 marks (2)

Question Number


2(d)(i) • 10.4/15.0 (1)

• (10.4/15.0) x100 (1) (= 69.3) 69.3 alone worth 2 marks If no/incomplete working shown answer to 2 or more sf scores 2 marks Ignore any units (2)


Question Number


2(d)(ii) Two suggestions from

• reaction incomplete (1)

• impure reactants (1)

• other unwanted/sidereaction(s) occur (1)

• product lost duringexperiment/practical (1)

reversible

ignore by-products form

could be an example eg some products left in apparatus

ignore generic experimental errors eg measuring/weighing errors/human error/spillage (2)


Dynamic Equilibria Mark Scheme

Level Edexcel

Subject Chemistry



Sub Topic Dynamic Equilibria

Booklet Mark Scheme


Score: /44

Percentage: /100


Question Number


1 (a) An explanation linking

Marking point 1 – one from • forward and back reactions

take place (at the sametime) (1)

• rate of the forward andback reactions is the same(1)

Marking point 2 – one from • no (overall) change in the

{amount/concentration/mass/ volume} of each{substance / reactant /product} (1)

• no observable change (1)

assume ‘both reactions’ implies the forward and back reaction

allow reversible reaction with the same rate (1) allow reversible reaction in a closed system (1) do not allow the forward reaction equals the reverse reaction

allow overall effect is nil (1) allow reactants and products reach a balance (1) ignore forward reaction cancels out back reaction do not allow {amount / concentration /mass/volume} of reactants and products are equal (2)

Question Number


1(b)(i) An explanation linking two of

• higher pressure favoursforward reaction/equilibriumshifts to the right (1)

• because decrease in{volume / number ofmolecules}/side with lowervolume (1)

• yield increases (1)

ignore answers related to rate/collisions

maximum (1) if 3 statements given, but 1 is incorrect

(2)

Question Number


1(b)(ii) An explanation linking any two of

• lower temperature favoursforward reaction/equilibriumshifts to the right (1)

• because (forward) reactionis exothermic (1)

• yield increases (1)

ignore answers related to rate/collisions

if answer refers to increasing temperature, maximum (1) for (forward) reaction is exothermic / reverse reaction is endothermic

maximum (1) if 3 statements given, but 1 is incorrect (2)


Question Number


1(b)(iii) catalyst iron (1)

Question Number


1(c)(i) 3 x 1000 (1) (= 3000) (1)

Question Number


1(c)(ii) marks are for the working

Method 1 14 + (3 x 1) (1) g of NH3 makes 14 + (4 x 1) + 14 + (3 x 16) (1) g NH4NO3

34 g of NH3 makes (14 + (4 x 1) + 14 + (3 x 16))x 34 or

17

80 x 34 or 17

2(14 + (4 x 1) + 14 + (3 x 16)) g NH4NO3

(1) = 160 g

Method 2 moles of NH3 = 34 (1) = 2

17

moles of NH4NO3 = moles of NH3 or relative formula mass NH4NO3 = 80 (1)

mass NH4NO3 = 2 x 80 (1) = 160 g

full marks awarded for an answer of 160 g with or without any working

allow ecf on incorrect Mr s for either method

allow ecf for incorrect moles eg if moles of NH3 = 0.5 relative formula mass NH4NO3 = 80 (1) mass NH4NO3 = 0.5 x 80 (1) = 40 g

(3)


Question number

Answer Mark

2(a)(i) An explanation that combines identification – understanding (1 mark) and reasoning/justification – understanding (2 marks): • rate increased/time to reach equilibrium reduced (1)• because gas molecules closer/more concentrated (1)• so increased collision rate/more frequent collisions(1) (3)

Question number

Answer Mark

2(a)(ii) A (1)

Question number

Answer Mark

2(b) equilibrium position/usefulness of by-products (1)


Question Number

Indicative content

2(c) Answers will be credited according to candidate's deployment of knowledge and understanding of the material in relation to the qualities and skills outlined in the generic mark scheme.

The indicative content below is not prescriptive and candidates are not required to include all the material which is indicated as relevant. Additional content included in the response must be scientific and relevant.

AO1 (6 marks) The effect of the temperature rise on the rate of attainment of equilibrium and on the equilibrium yield are considered by: • higher temperature reaches equilibrium faster because molecules

move faster• therefore there are more frequent collisions because molecules have

more energy• therefore more collisions have required energy but yield will be lower• because higher temperature favours endothermic reaction and so

equilibrium shifts to left hand side• which is decomposition of ammonia / ammonia reforms elements• catalyst causes reaction to reach equilibrium faster / catalyst

increases rates (of both forward and back reactions)• lowers the activation energy (of both forward and back reactions) but

does not affect yield• equilibrium position not affected.

Level Mark Descriptor 0 No rewardable material.

Level 1 1-2 • Demonstrates elements of chemical understanding, some ofwhich is inaccurate. Understanding of scientific ideas lacksdetail. (AO1)

• Presents an explanation with some structure and coherence.(AO1)

Level 2 3-4 • Demonstrates chemical understanding, which is mostlyrelevant but may include some inaccuracies. Understanding ofscientific ideas is not fully detailed and/or developed. (AO1)

• Presents an explanation that has a structure which is mostlyclear, coherent and logical. (AO1)

Level 3 5-6 • Demonstrates accurate and relevant chemical understandingthroughout. Understanding of the scientific ideas is detailedand fully developed. (AO1)

• Presents an explanation that has a well-developed structurewhich is clear, coherent and logical. (AO1)


Question Number


3(a) B 200 cm3 (1)

Question Number


3(b) 65.0 g Zn produces 24 dm3 H2 (1)

13.0 g Zn produces 13.0 x 24 (1) 65.0

(= 4.8 dm3 H2)

13.0 mol Zn produces 13.0 mol H2 65.0 65.0

Vol of H2 = 13.0 x 24 (2) (= 4.8dm3)

65.0

4.8 dm3 (2) without working

allow 65/13 x 24 (1) = 120dm3

13/65 (1) x (1/24) = 0.00833 dm3

0.2 anywhere 1 mark

x 24 anywhere 1 mark

(2)

Question Number


3(c)(i)) natural gas (1)

Question Number


3(c)(ii) An explanation linking

forward and back reactions take place / reversible / dynamic (1)

at the same rate / equilibrium (1)

dynamic equilibrium = 2 marks

(2)


Question Number


QWC *3(d) A description including some of the following points

Higher pressure: higher pressure gives increased yield equilibrium shifts to right hand side because decrease in number of molecules going from left to

right therefore decrease in volume favoured by increase in pressure reaches equilibrium faster because molecules closer together so get more frequent collisions

Higher temperature higher temperature reaches equilibrium faster because molecules move faster therefore more frequent collisions molecules have more energy therefore more collisions have required energy but yield will be lower because higher temperature favours endothermic reaction equilibrium shifts to left hand side which is decomposition of ammonia / ammonia reforms

elements

Use of catalyst catalyst causes reaction to reach equilibrium faster /

catalyst increases rates (of both forward and back reactions) lowers the activation energy (of both forward and back

reactions) reaction follows a new pathway does not affect yield equilibrium position not affected (6)


LevelLev No rewardable content 1 1 - 2 a limited description e.g. one valid effect of change OR general

comment indicating improved yield or faster rate the answer communicates ideas using simple language and uses

limited scientific terminology spelling, punctuation and grammar are used with limited

accuracy2 3 - 4 a simple description e.g. at least two valid effects of change with

one point of explanation OR at least three valid effects of change the answer communicates ideas showing some evidence of clarity

and organisation and uses scientific terminology appropriately spelling, punctuation and grammar are used with some accuracy

3 5 - 6 a detailed description e.g. at least three valid effects of changewith two points of explanation OR at least two valid effects withthree points of explanation (in total)

the answer communicates ideas clearly and coherently uses arange of scientific terminology accurately

spelling, punctuation and grammar are used with few errors


Question Number

Answer Mark

4(a)

any 3 carbon molecule and one C=C (1) fully correct molecule with all bonds (2)

(2)

Question

Number


4(b)(i) A 333 dm3 (1)

Question Number


4(b)(ii) An explanation linking all / three gases present/

nitrogen, hydrogen andammonia (1)

ammonia decomposes/ammonia turns back toreactants/ reaction goes

both ways / reversible (1)

reject ammonium

ignore incomplete reaction assume that “both reactions” refer to forward and backward

reaction allow dynamic equilibrium

(2)

Question

Number


4(b)(iii) An explanation linking

increased / higher {yield /amount of ammonia} (1)

because fewer (gas)molecules/ moles on RHS/

4 mole(cule)s on left and2 on right/ decreased

volume onRHS/equilibrium shifts toRHS/ equilibrium shifts in

forward direction (1)

mark independently

ignore “high yield”

reject answers referring to exothermic or endothermic

ignore any references to rate

(2)


Question Number


4(b)(iv) An explanation to include

rate increased/ time to

reach equilibrium reduced(1)

because gas moleculescloser / more concentrated(1)

so increased collision rate/ more collisions in a

given time / more frequentcollisions(1)

mark independently

ignore any refs to equilibrium

ignore ‘time is faster’/ allow ‘quicker’

allow atoms/ particles instead of molecules; allow more molecules

present (in same container) do not allow ‘more collisions’

(3)

Documents

Transition Metals, Alloys & Corrosion · 2018-05-25 · è á ZZZ VDYHP\H[DPV FR XN 2 3 - 4 • a simple description containing two statements referring to one method of extraction