MakingSolubleSalts

1. Writeawordequationforthereactioninthisexperiment.

Copperoxide+sulphuricacidàcoppersulphate+water

2. Completethefollowingequations:

Coppercarbonate+Sulphuricacidàcoppersulphate+carbondioxide+water

Sodiumhydroxide+Hydrochloricacidàsodiumchloride+water

Zincoxide+NitricacidàZincNitrate+Water

Coppercarbonate+hydrochloricacidàcopperchloride+carbondioxide+water

3. Instep4,youareadvisedtoensureyoukeepaddingcopperoxideuntilsomeofitstillremainsafterstirring.Thisisknownasaddingthecopperoxidein‘excess’.Explainwhythisisimportant.Toensurethatalloftheacidhascompletelyreacted

4. Instep5,youareaskedtofilterthesolution.Explainwhythisisimportant.Toremovetheexcesscopperoxide/base

5. Whatdoesthetermfiltratemean?Thisistheliquidthatpassesthroughthefilterpaperandcollectsintheconicalflask.Inthisexampleitisthesaltsolution.

M1. nitric acid 1

potassium hydroxide 1

water 1

[3]

M2. (a) (i) water accept H2O accept correct ringed answer in box

1

(ii) neutralisation accept underlining or any indication, eg tick

1

(b) sodium hydroxide 1

sulphuric acid apply list principletotal

1 [4]

M3.(a) s 1

l Answers must be in the correct order.

1

(b) A gas was lost from the flask 1

(c) Level 3 (5–6 marks): A coherent method is described with relevant detail, and in correct sequence which demonstrates a broad understanding of the relevant scientific techniques and procedures. The steps in the method are logically ordered. The method would lead to the production of valid results.

Level 2 (3–4 marks): The bulk of the method is described with mostly relevant detail, which demonstrates a reasonable understanding of the relevant scientific techniques and procedures. The method may not be in a completely logical sequence and may be missing some detail.

Level 1 (1–2 marks): Simple statements are made which demonstrate some understanding of some of the relevant scientific techniques and procedures. The response may lack a logical structure and would not lead to the production of valid results.

0 marks: No relevant content.

Indicative content • sulfuric acid in beaker (or similar) • add copper carbonate one spatula at a time • until copper carbonate is in excess or until no more effervescence

occurs * • filter using filter paper and funnel • filter excess copper carbonate • pour solution into evaporating basin / dish • heat using Bunsen burner • leave to crystallise / leave for water to evaporate / boil off water • decant solution • pat dry (using filter paper) • wear safety spectacles / goggles

*Students. may choose to use a named indicator until it turns a neutral colour, record the number of spatulas of copper carbonate added then repeat without the indicator.

6

(d) Total mass of reactants = 221.5 1

159.5

221.5 allow ecf from step 1

1

72.0 (%) 1

allow 72.0 with no working shown for 3 marks

(e) any one from:

• Important for sustainable development • Economic reasons • Waste products may be pollutants / greenhouse gases

1 [13]

M4. (a) (i)

calcium carbonate

→ calcium oxide

+ carbon dioxide

accept CaO3 → CaO + CO2

1

(ii) (thermal) decomposition accept endothermic accept reversible

1

(b) (i) neutralisation accept exothermic

1

(ii) sulphuric (acid) H2SO4

2

(c) (i) to speed up the reaction accept to increase the rate of reaction or to increase the number or rate of collisions do not accept “dissolves” copper oxide faster

1

(ii) all acid reacts accept there will be no acid left or acid used up

1

acid is neutralised (for 2 marks) do not accept to form a concentrated or saturated solution

1

(excess) copper oxide collects in filter paper accept larger particles (of copper oxide) cannot pass through filter paper

1

copper sulphate solution passes through the filter paper accept dissolved copper sulphate passes through filter paper or smaller particles (of copper sulphate) in solution (liquid) pass through filter paper accept (black) solid collects in filter paper and filtrate or soluble solid or (blue) solution (liquid) passes through filter paper for 1 mark only

1 [10]

M5.(a) neutralisation ignore reference to exothermic or endothermic

1

(b) 2 HCl + CaO ➔ CaCl2 + H2O accept multiples and fractions

formulae ignore state symbols

1

balancing (dependent on first mark) 1

(c) (the carbonate has) fizzing / bubbles / effervescence ignore dissolving ignore gas produced

1

(d) add excess calcium carbonate to acid (and stir) / add CaCO3 until fizzing stops

ignore heating the acid accept answer using calcium oxide in place of calcium carbonate

1

(remove excess calcium carbonate by) filter(ing) 1

warm until a saturated solution forms / point of crystallisation / crystals start to form

do not accept heat until all water gone 1

leave to cool dependent on previous mark If solution not heated allow leave to evaporate (1) until crystals form (1)

1

(e) (i) white precipitate / solid (forms) 1

insoluble in excess or remains or no (further) change in excess dependent on a precipitate / solid forming

1

(ii) same result with magnesium (ions) do not accept reference to any other ion(s) that do not give a white precipitate

accept other named ions that do give a white precipitate

1

(iii) flame test or description of flame test 1

gives a red flame accept brick red or orange-red or scarlet do not accept crimson

1 [13]

Neutralisation:1.Whatistheindicatorcalledinthisexperiment?Methylorange

2.Whatistheindicatorusedfor?Colourchangeindicateswhenneutralpointhasbeenreachedandsotheendpointoftheexperiment

M1.(a) (i) (19.5 + 18.5 + 19.0) / 3 allow (23.0 + 19.5 + 18.5 + 19.0) / 4 for 1 mark

2

(ii) R P Q allow Q P R for 1 mark

2

(b) any two from: • repeat more times • calculate a mean • measure to one decimal place.

2

(c) both students get similar results / similar pattern 1

[7]

M2.(a) (i) burette

1

(ii) indicator 1

(iii) colour change 1

(b) (i) any one from: • volume of (hydrochloric) acid

allow amount of (hydrochloric) acid • concentration of (hydrochloric) acid • concentration of (sodium) hydroxide

allow concentration of alkali 1

(ii) 22.3(0) 1

[5]

M3.(a) (i) H+

1

(ii) OH–

1

(b) with ethanoic acid: ‘it’ refers to ethanoic acid

UI goes Orange/yellow 1

but HCl goes red/pink 1

or

ethanoic acid has pH 4 or above but less than 7 (1)

but HCl has a pH3 / or lower (1)

(c) completely 1

(d) (i) conical flask 1

(ii) titration 1

(iii) repeatortake average allow compare with another student's results

1 [8]

M4. (a) burette 1

(b) indicator changed colour allow any indication of colour change

1

(c) (i) 0.2 or 18.3 to 18.5 1

(ii) 18.4 1

(iii) improve reliability allow improve accuracy

allow to calculate a mean / average or get rid of anomalous result ignore fair test / correct results / random results

1 [5]

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

Level 3 (5 – 6 marks) There is a description of titrations that would allow a comparison to be made between the two solutions of hydrochloric acid.

Level 2 (3 – 4 marks) There is a description of an experimental method including addition of acid to alkali which may include an indicator or colour change and may include a measurement of volume.

Level 1 (1 – 2 marks) There is a simple description of using some of the apparatus.

0 marks No relevant content.

examples of chemistry points made in the response could include: • acid in burette or flask • alkali/sodium hydroxide or acid in burette or flask • volume of acid or alkali measured using the pipette • indicator in flask • white tile under the flask • slow addition • swirling/mixing • colour change of indicator • burette volume measured

[6]

Neutralisation – Higher only CalculationsStep1

Molesofsodiumhydroxidein25cm3=concentration´volume=0.1mol/dm3´(25÷1000)dm3

= 0.0025

moles Step2

Equation:2NaOH+H2SO4àNa2SO4+2H2OThisshowsthattwomolesofsodiumhydroxideneutraliseonemoleofsulfuricacid.So moles of sulfuric acid used = (answer from step 1) ÷ 2

= 0.00125

moles Step3

Concentrationofsulfuricacid(mol/dm3)=moles÷meanvolumeofacid =(answerfromstep2)÷(meanvolumefromtable÷1000)meanfromtable24.8–repeat3excludedso0.00125/0.0248=

= 0.050

mol/dm3 Step4

Ar(H)=1;Ar(O)=16;Ar(S)=32

Mr (H2SO4) = 98

Concentrationofsulfuricacid(g/dm3)=(answerfromstep3)xMr(H2SO4)

Concentration(mol/dm3)=numberofmoles÷volumeofsolution(dm3)

Numberofmoles=massofsubstance(g)÷Mrofsubstance

= 4.9

g/dm3

M2.(a) 31 1

(b) (i) any two from: • incorrect reading of thermometer / temperature • incorrect measurement of volume of acid • incorrect measurement of volume of alkali (burette).

2

(ii) glass is a (heat) conductor or polystyrene is a (heat) insulator answer needs to convey idea that heat lost using glass or not lost using polystyrene accept answers based on greater thermal capacity of glass (such as “glass absorbs more heat than polystyrene”)

1

(c) (i) temperature increases 1

(ii) no reaction takes place or all acid used up or potassium hydroxide in excess

1

cool / colder potassium hydroxide absorbs energy or lowers temperature

ignore idea of heat energy being lost to surroundings 1

(iii) take more readings ignore just “repeat”

1

around the turning point or between 20 cm3 and 32 cm3

accept smaller ranges as long as no lower than 20 cm3 and no higher than 32 cm3

1

(d) 1.61 or 1.6(12903) correct answer with or without working scores 3

if answer incorrect, allow a maximum of two from: moles nitric acid = (2 × 25 / 1000) = 0.05 for 1 mark moles KOH = (moles nitric acid) = 0.05 for 1 mark concentration KOH = 0.05 / 0.031 answer must be correctly rounded (1.62 is incorrect)

3

(e) same amount of energy given out 1

which is used to heat a smaller total volume or mixture has lower thermal capacity or number of moles reacting is the same but the total volume / thermal capacity is less

if no other marks awarded award 1 mark for idea of reacting faster

1 [14]

M3. (a) must be description of a titration no titration = no marks

NaOH in burette do not accept biuret etc

1

add NaOH until (indicator) changes colour if specific colour change mentioned, must be correct – colourless to pink / red or ‘goes pink / red’ do not accept ‘clear’ for colourless

1

note (burette) volume used or final reading accept ‘work out the volume’

1

one other point: eg repeat accept: (white) tile or add dropwise / slowly or white background or swirling / mix or read meniscus at eye level or wash apparatus

1

(b) 0.054 for 2 marks (0.1 × 13.5)/25 for 1 mark

(c) don’t know – insufficient evidence to decide owtte any sensible answer

or

depends on whether acid level is considered safe or unsafe

yes, safe – acid level low / weak acids / low compared with stomach acid owtte any sensible answer

2

no, unsafe – acid level (too) high / other substances or bacteria may be present / insufficient evidence to decide

owtte any sensible answer

1

(d) (methyl orange) would have changed colour (well) before the end-point / pH7 / neutral

owtte 1

weak acid present weak acid-strong base (titration) allow methyl orange used for strong acid-weak base titration

1 [9]

Electrolysis

Questions

1. Whatisthenameforthepositiveelectrode?anode2. Whatisthenameforthenegativeelectrode?cathode

3. Whenlitmuspaperisbleached,whatgasispresent?chlorine4. Howdoyoutestagastofindoutifitisoxygen?Re-lightsaglowingsplint5. Howdoyoutestagastofindoutifitishydrogen?Squeakypoptest6. Howdoyoutestagastofindoutifitiscarbondioxide?Turnslimewatercloudy

M1.(a) electricity allow an electric current

1

(b) (i) chlorine/Cl2

do not accept chloride 1

(ii) (zinc ions are) positive ignore to gain electrons

1

and (opposite charges) attract 1

(iii) reduction 1

(c) (i) in alloy: accept converse

different sized atoms/particles

or

no layers/rows accept layers distorted

1

so cannot slide 1

(ii) shape memory (alloys) accept smart

1 [8]

M2. (a) (i) electron(s) allow free / delocalised / negative electrons do not accept additional particles

1

(ii) ion(s) allow named ions from table ignore positive or negative do not accept additional particles

1

(b) (i) copper accept Cu do not accept Cu2+

1

(ii) it is / they are positive (ions) accept formula of positive ion

1

and it is the least reactive 1

(c) (i) loss of electron(s) ignore numbers

1

(ii) 2H+ + 2e– → H2

accept correct multiples / fractions accept e / e–

allow 2H+ → H2 – 2e–

1 [7]

M3. (a) the ions can move / travel / flow /are free accept particles / they for ions allow delocalised ions

or ignore delocalised / free electrons ignore references to collisions accept converse with reference to solid

the ions carry the charge / current ignore ions carry electricity

1

(b) any one from:

• because they are negative / anion allow Cl–

ignore chlorine

• opposite charges / attract 1

(c) 13 1

(d) (i) reasonable attempt at straight line which misses the anomalous point must touch all five crosses do not allow multiple lines

1

(ii) 40 ignore 2.2

1

(iii) any two sensible errors from: ignore systematic / human / apparatus / zero /experimental / random / measurement / reading errors unless qualified

• gas escapes

• weighing error allow NaCl not measured correctly

• error in measuring (volume / amount) of hydrogen

• error in measuring (volume / amount) of water allow error in measuring volume / scale for 1 mark if neither hydrogen or water mentioned

• incorrect concentration allow NaCl not fully dissolved or spilled or impure

• timing error

• change in voltage / current allow faulty power supply

• change in temperature

• recording / plotting error 2

(iv) any one from: ignore ‘do more tests’

• repeat the experiment

• results compared with results from /other students / other groups / other laboratories / internet / literature.

• results compared with another method 1

(v) increases owtte allow directly proportional or positive correlation allow rate / it is faster / quicker

1 [9]

M4. (a) electric current / electricity 1

plus one from:

• is passed through ionic compound / substance / electrolyte

• passed through molten/aqueous compound / substance must be linked to electricity allow liquid compound / substance do not allow solution / liquid alone

• causing decomposition accept split up / breakdown / breaking up owtte ignore separated accept elements are formed ignore new substances form

1

(b) hydrogen accept H2

do not accept H / H2

1

(c) one electron from each atom accept each carbon is bonded to three other carbon atoms leaving one (unbonded) electron owtte

1

is delocalised / free (to move) must be linked to electrons answers of delocalised / free electrons only, gains 1 mark accept each carbon is bonded to three other carbon atoms leaving delocalised / free electrons = 2 marks maximum 1 mark if graphite described as a metal / giant ionic lattice

1 [5]

Neutralisation Questions

1. Whenthesodiumhydroxideandthehydrochloricacidareaddedtogether,thetemperaturerises.Whattypeofreactionisthis,endothermicorexothermic?Explainyouranswer.Exothermicreaction,moreenergyreleasedwhenbondsinproductsformthanisusedtobreakthebondsinthereactantssoenergyisreleasedbythereaction

2. Explainwhytheexperimentiscarriedoutinaninsulatedcup.Minimiseheat/energylossesfromtheexperiment.

3. Explainwhyyoudrawtwolinesonthegraphasdescribedinstep8.Inordertoextrapolate/determinethehighesttemperatureachieved.

M1.(a) eg plastic (beaker) / insulation / lid / cover or any mention of enclosed any sensible modification to reduce heat loss ignore prevent draughts ignore references to gas loss ignore bomb calorimeter

1

(b) all the substances react or all (the substances) react fully / completely or heat evolved quickly or distribute heat

‘so they react’ is insufficient for the mark accept increase chances of (successful) collisions /

collision rate increase do not accept rate of reaction increase / make reaction faster

1

(c) experiment 2 and different / higher / initial / starting temperature

accept experiment 2 and the room is hotter / at higher temperature do not accept temperature change / results higher

1

(d) temperature change does not fit pattern accept anomalous / odd or it is the lowest or it is lower than the others or it is different to the others ‘results are different’ is insufficient

1

(e) 7 / 7.0 1

(f) (100 × 4.2 × 7) = 2940 ecf from (e)

1

(g) diagram A and reaction exothermic / heat evolved / Δ H is negative / temperature rises

accept energy is lost (to the surroundings) accept energy of products lower than reactants allow arrow goes downwards

1 [7]

M2.(a) (i) any one from:

• incorrect measurement of temperature or volume • incorrect recording of temperature • failure to stir • heat loss

ignore faulty equipment 1

(ii) 32 - 33 1

(iii) 55 1

(iv) 20 1

(v) 4620 allow 4.62 kJ for 2 marks

1

J / joules allow kJ if evidence of dividing by 1000 mark independently, but if a numerical answer has been divided by 1000 must be kJ. allow ecf from their answers to (iii) and (iv)

1

(b) twice as much energy released 1

but twice as much water to heat allow more energy released but more water to heat for

2 marks if no other mark awarded, allow twice the amount of hydrochloric acid used for 1 mark

1 [8]

Rates – activity 1 questions 1. Whatistheindependentvariableinthisreaction?Concentrationofsodiumthiosulpahte2. Whatistherangeoftheindependentvariableinthisreaction?8-40g/dm33. Whatisthedependentvariable?Timetakenforthecrosstodisappear4. Whatarethecontrolvariablesforthisreaction?Volumeofsdiumthiosulpahte,concentrationand

volumeofhydrochloricacid,temperatureofthesolutions,presenceorabsenceofcatalyst5. Explainwhythecrossdisappearsfromview.Solidsulphurisoneoftheproductsandasitis

producedmakesthesolutionbecomecloudyobscuringthecrossfromview.6. Whatpatternwouldyouexpecttoseeinthisexperiment?Explainyouranswer.Increasing

concentrationincreasestherateofreaction.Athigherconcentrationthereisalargenumberofparticlesinagivenvolumeandthisincreasesthechanceofparticlescolliding,whichinturnincreasestherateofreaction.

7. Whatdoyouthinkwillbethebiggestsourceoferrorinthisexperiment?Explainyouranswer.Judgingwhenthecrossdisappears,itssubjective/dependentondifferentpeople’sopinions.Sothesamepersonshouldjudgethiseachtime.QuestionsRatesactivity2

1. Whatwastheindependentvariable?Concentrationofhydrochloricacid

2. Whatwasthedependentvariable?Volumeofgasproduced3. Whatarethemaincontrolvariables?Volumeofacid,mass/size/amount

ofmagnesium,temperatureofthereactions,surfaceareofthemagnesium,presence/absenceofacatalyst

4. Describeandexplainthepatternyouwouldexpecttosee.Increasingconcentrationshouldleadtogasbeingproducedmorequickly/largervolumesofgas.Athigherconcentrationthereisalargenumberofparticlesinagivenvolumeandthisincreasesthechanceofparticlescolliding,whichinturnincreasestherateofreaction.

5. Insteadofanupsidedownmeasuringcylinderinatroughofwater,whatalternativepieceofequipmentcouldbeusedtomeasurethevolumeofgasproduced.Gassyringe

M1.(a) 36 cm3

1

(b) all points correct ± ½ small square

2

allow 1 mark if 6 or 7 of the points are correct

2 best fit lines drawn must not deviate towards anomalous point

2

allow 1 mark if 1 line correct

(c) The bung was not pushed in firmly enough. 1

The measuring cylinder was not completely over the delivery tube. 1

(d) as mass of lithium carbonate increases volume of gas produced increases 1

linear / (directly) proportional 1

(e) A gas / carbon dioxide is produced. allow because the air in the tube expands

1

(f) any one from: • Potassium carbonate does not decompose to produce carbon dioxide / a

gas.

• Potassium carbonate does not decompose at the temperature of the Bunsen burner or the Bunsen burner is not hot enough to decompose potassium carbonate.

• When potassium carbonate decomposes a gas is not formed. 1

[11]

M2.(a) cotton wool 1

(b) all points correct ± ½ small square

2

allow 1 mark if 5 or 6 of the points are correct

best fit line must not deviate towards anomalous point

1

(c) (mass) 2.1 (g)

allow ecf from drawn best fit line 1

(time) 100 (s)

1

(d) a gas is produced 1

which escapes from the flask 1

(e) 1

0.07 (g / s) allow ecf answer correctly calculated to 2 decimal places

1

(f) collect the gas in a gas syringe 1

measured the volume of gas allow carbon dioxide for gas

1

allow for 1 mark collected gas or counted bubbles

(g) The particles have more energy 1

The particles move faster 1

[14]

M3.(a) because sulfur / S (forms) 1

(which) is solid / insoluble / a precipitate / a suspension 1

(b) any two from: • volume of sodium thiosulfate

ignore amount of sodium thiosulfate • volume of (hydrochloric) acid

ignore amount of (hydrochloric) acid • concentration of sodium thiosulfate • concentration of (hydrochloric) acid

if no other mark, allow 1 mark for same cross or same flask or unspecified volume or unspecified concentration ignore same person do not accept references to temperature

2

(c) rate increases 1

because particles move faster accept particles have more energy

1

so frequency of collisions increases accept particles are more likely to collide or more chance of collisions ignore more collisions

1

more particles / collisions have energy greater than (or equal to) the activation energy

1

(d) cool

accept refrigerate or method to decrease temperature or

decrease the temperature (of the solutions) 1

[9]

M4.(a) CaCO3 + 2HCl → CaCl2 + H2O + CO2 2

allow 1 mark for correct formulae

(b) sensible scales, using at least half the grid for the points 1

all points correct ± ½ small square allow 1 mark if 8 or 9 of the points are correct

2

best fit line 1

(c) steeper line to left of original 1

line finishes at same overall volume of gas collected 1

(d) acid particles used up allow marble / reactant used up

1

so concentration decreases allow surface area of marble decreases

1

so less frequent collisions / fewer collisions per second do not accept fewer collisions unqualified

1

so rate decreases / reaction slows down 1

(e) mass lost of 2.2 (g) 1

time taken of 270 s

allow values in range 265 − 270 1

allow ecf for values given for mass and time

1

0.00815 (g / s)

or

8.15 × 10−3

allow 1 mark for correct calculation of value to 3 sig figs accept 0.00815 or 8.15 × 10−3 with no working shown for 4 marks

1

(f) correct tangent

1

eg 0.35 / 50 1

0.007 allow values in range of 0.0065 − 0.0075

1

7 × 10−3

1

accept 7 × 10−3 with no working shown for 4 marks [20]

IdentifyingIonsQuestions

1. Asolutionistestedithasalilacflame,noprecipitateisformedwiththehalideorsulphatetests,butitdoesfizzandturnlimewatercloudywhenitreactswithhydrochloricacid.Namethesaltpresent.Potassiumcarbonate

2. Asolutionistesteditburnswithacrimsonflameandwhenreactedwithdilutehydrochloricacidandbariumchlorideawhiteprecipitateisformed.Namethesaltpresent.LithiumSulfate

3. Asolutionwhenreactedwithdilutenitricacidandsilvernitratesformsayellowprecipitateandburnswithagreenflame.NamethesaltcopperIodide

M1. (a)

all three correct = 2 one or two correct = 1

2

(b) blue 1

precipitate solid

1 [4]

M2.(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]

M3.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]

WaterPurityQuestions

1. Step7asksyoutoplacethemixtureinabeakeroficeandwater.Explainwhythisstepisnecessary.Thiscoolsthesteam/gas/watervapoursoitcondensesintoaliquidinthetube

2. Insteps1–4crystalsshouldformonthewatchglassbeforethewaterhasbeendistilled.Explainwhythisis.Therewillbedissolvedchemicalssuchassaltsandmineralionsinthewater,thesewillbeleftbehindwhenthewaterevaporates.

3. Afterthewaterhasbeendistilledthereshouldbelittleornosolidonthewatchglass,explainwhy.Distillationseparateschemicalsdependingonboilingpoint–watershouldbepureasweheatthewaterto100oC(boilingpointofwaterandcollectthegas)wedonotheatthesolutionhighenoughfortheimpuritiestoevaporatesotheywillbeleftbehindintheconicalflask.

M1.(a) any one from:

• heat • stir

1

(b) filter accept use a centrifuge accept leave longer (to settle)

1

(c) any one from:

• wear safety spectacles • wear an apron

1

(d) evaporation at A 1

condensation at B 1

(e) 100 1

[6]