12.3 Acids Bases and Salts Ms - Igcse Cie Chemistry - Ext Theory Paper

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Acids, Bases and Salt

Mark Scheme 3
Level IGCSE
Subject Chemistry
ExamBoard CIE
Topic Acid, Bases and Salt
Sub-Topic
Paper (Extended) Theory
Booklet Mark Scheme 3
TimeAllowed: 83 minutes
Score: / 69
Percentage: /100
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1 (a giant covalent; [1]

or: polymer made from monomers;
(b)
b) ( any three from:
high mp / bp;
hard;
brittle;
insoluble (in water);
poor conductor of electricity / heat; [3]
(ii) carbon / diamond / silicon / boron; [1]

not: graphite
(c)
c) ( sodium hydroxide / any named alkali / reactive metal; [1]
(ii) named acid; [1]

zirconium oxide; [1]
[Total: 8]
2 (a 3 bp and 1nbp around phosphorus [1]

1 bp and 3nbp around each chlorine [1]
(b) (i) PCl3 + 3H2O → 3HCl + H3PO3 [1]
(ii) acid solutions same concentration [1]

measure pH/pH paper/Universal indicator [1]
hydrochloric acid lower pH [1]
colours of Universal indicator can be given as red<orange<yellow

ignore precise pH values as long as HCl is lower than H3PO3
OR Acid solutions same concentration [1]

add magnesium or any named metal above Hydrogen in reactivity series but not above
magnesium
calcium carbonate or any insoluble carbonate [1]
hydrochloric acid react faster/shorter time [1]
OR acid solutions same concentration [1]

measure electrical conductivity [1]
hydrochloric acid better conductor/bulb brighter [1]
OR acid solutions same concentration [1]

add sodium thiosulphate [1]
hydrochloric acid forms precipitate faster/less time [1]
(iii) sodium hydroxide/sodium carbonate [1]

titration cond on correct reagent [1]
second mark scores for mention of titration /burette/pipette/indicator.
experimental detail not required
any named soluble calcium salt e.g. calcium chloride/nitrate/hydroxide [1]
precipitation/filter/decant/centrifuge
rec
3 (a (i) lithium oxide / strontium oxide [1]
(ii) sulfur dioxide / nitrogen dioxide [1]
(iii) aluminium oxide [1]
(iv) carbon monoxide [1]

accept: correct formulae
(b) sulfur dioxide [1]

burn (fossil) fuel containing sulfur / volcanoes [1]
nitrogen dioxide [1]
reaction of nitrogen and oxygen [1]
high temperatures / in car engine [1]
not: exhaust
(c) (i) strontium oxide [1]

accept: aluminium oxide
(ii) use correct formula [1]

cond: charges on ions
6x and 2o around oxygen [1]
ignore: electrons around Li
4 (a (i) to neutralise all the acid / so all acid reacts [1]

not: reaction goes to completion
(ii) remove excess carbonate / removes unreacted carbonate [1]

not: remove solid
(iii) need water of crystallisation / hydrated crystals / to get crystals [1]
(iv) filter / decant / wash crystals [1]

dry with filter paper or tissues etc. [1]
accept: in warm oven / warm place / in sun
not: just heat
(b)
b) ( potassium carbonate is soluble / both salts soluble [1]
(ii) use potassium carbonate solution [1]

accept: implication of solution – in pipette / burette / 25 cm3
titrate / titration term required [1]
use an indicator accept: any named acid/base indicator [1]
repeat without indicator / use carbon to remove indicator [1]
(c) mass of hydrated magnesium sulfate = 1.476 g

mass of barium sulfate formed = 1.398 g
the mass of one mole of BaSO4 = 233 g
the number of moles of BaSO4 formed = 0.006 [1]
the number of moles of MgSO4.xH2O used in experiment = 0.006 [1]
the mass of one mole of MgSO4.xH2O = 1.476/0.006 = 246 g [1
the mass of xH2O in one mole of MgSO4.xH2O = 246 – 120 = 126 g [1
x = 126/18 = 7 [1]
if x given without method = max 1
note: apply ecf but x must be an integer and less than 10
5 (a)
a) ( Tl 2S [1]
(ii) TlCl 3 [1]
(b) filter / centrifuge / decant

wash the precipitate
dry the solid / heat the solid (in oven) / press between filter paper [3]
all three stated but not in correct order = [2]

two out of three stated in any order = [1]
(c) (i) silver chloride / silver bromide [1]

photography / cameras / films / photo chromic lenses / sunglasses [1]
(ii) increase distance between lamp and paper or put lamp far away /
put a screen or translucent or semi-opaque material between them /
use a less powerful or low voltage or dim lamp /
lower the temperature
any two [2]
(d)
d) ( thalium sulfate + ammonia + water [1]
(ii) 2TlOH + H2SO4 Tl2SO4 + 2H2O [2

not balanced = [1]
incorrect formula = [0]
(iii) green precipitate or solid (ignore shades of green but not bluey green etc.) [1]
Fe2+ + 2OH– Fe(OH)2 accept multiples [1]
6 (a filter / centrifuge / decant [1]

(partially) evaporate / heat / boil [1]
allow to crystallise / cool / let crystals form [1]
dry crystals / dry between filter paper / leave in a warm place to dry [1]
“dry” on its own must be a verb
evaporate to dryness only marks 1 and 2
note if discuss residue only mark 1
(b) number of moles of HCl used = 0.04 × 2 = 0.08

number of moles CoCl2 formed = 0.04
number of moles CoCl2.6H2O formed = 0.04
mass of one mole of CoCl2.6H2O = 238 g
maximum yield of CoCl2.6H2O = 9.52g [4]
accept 9.5 g
mark ecf to moles of HCl
do not mark ecf to integers
to show that cobalt(II) carbonate is in excess
number of moles of HCl used = 0.08 must use value above ecf
mass of one mole of CoCO3 = 119g
number of moles of CoCO3 in 6.0g of cobalt(II) carbonate = 6.0/119 = 0.050 [1]
reason why cobalt(II) carbonate is in excess 0.05 > 0.08/2 [1]
[Total: 10]

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Acids, Bases and Salt

1 (a giant covalent; [1]

(ii) carbon / diamond / silicon / boron; [1]

(ii) named acid; [1]

2 (a 3 bp and 1nbp around phosphorus [1]

(b) (i) PCl3 + 3H2O → 3HCl + H3PO3 [1]

(ii) acid solutions same concentration [1]

colours of Universal indicator can be given as red<orange<yellow

OR Acid solutions same concentration [1]

OR acid solutions same concentration [1]

OR acid solutions same concentration [1]

(iii) sodium hydroxide/sodium carbonate [1]

any named soluble calcium salt e.g. calcium chloride/nitrate/hydroxide [1]

3 (a (i) lithium oxide / strontium oxide [1]

(ii) sulfur dioxide / nitrogen dioxide [1]

(iii) aluminium oxide [1]

(iv) carbon monoxide [1]

(b) sulfur dioxide [1]

(c) (i) strontium oxide [1]

(ii) use correct formula [1]

4 (a (i) to neutralise all the acid / so all acid reacts [1]

(ii) remove excess carbonate / removes unreacted carbonate [1]

(iii) need water of crystallisation / hydrated crystals / to get crystals [1]

(iv) filter / decant / wash crystals [1]

(ii) use potassium carbonate solution [1]

(c) mass of hydrated magnesium sulfate = 1.476 g

(ii) TlCl 3 [1]

(b) filter / centrifuge / decant

all three stated but not in correct order = [2]

(c) (i) silver chloride / silver bromide [1]

(ii) 2TlOH + H2SO4 Tl2SO4 + 2H2O [2

6 (a filter / centrifuge / decant [1]

(b) number of moles of HCl used = 0.04 × 2 = 0.08

to show that cobalt(II) carbonate is in excess

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