Page 61 - ACE YR IGCSE A TOP APPROACH TO CHEM

12 D (d) Nitric acid
Oxygen: glowing splint re-light / lighted splint burns Nitric acid is made up of H and NO . After the
+
–
3
brighter. reaction is complete, copper ions from copper(II)
Hydrogen: lighted splint makes a squeaky ‘pop’. oxide will chemically join with nitrate ions to form
Chlorine: damp red litmus paper is bleached. copper(II) nitrate.
Carbon dioxide: limewater turns milky / cloudy.
(e) Black solid dissolves. [1]
Part 2: Structured Questions The solution turns blue. [1]
1 (a) Simple distillation [1] Copper(II) oxide is a black solid. Copper(II) nitrate is
blue and it is soluble.
Simple distillation is used to separate liquids with
different boiling points. Salt has a much higher (f) Copper(II) oxide + nitric acid ➞ copper(II)
boiling point than water. Simple distillation is nitrate + water [1]
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suitable to obtain water.
(g) 2Cu(NO ) ➞ 2CuO + 4NO + O
(b) Paper chromatography [1] 3 2 2 2
Carotene and xanthophyll are pigments in leaves. Correct formula for two products [1]
They can be separated using paper chromatography. Balanced equation [1]
(c) Fractional distillation [1] 4 (a) Fractional distillation [1]
Crude oil contains different types of hydrocarbons. (b) Liquefied the mixture of gases [1]
The difference in boiling points can be small. Heat [1]
Fractional distillation is suitable to separate them.
Condense / cool [1]
(d) Crystallisation [1]
Copper(II) sulfate is a salt. (c) The gases have different boiling points. [1]
(e) Diffusion [1] (d) Nitrogen [1]
Oxygen and carbon dioxide have different relative The gas with the lowest boiling point will evaporate
molecular masses. They will diffuse at different first.
speeds. (e) Glass beads increase the surface area. [1]
(f) Filtration [1] It will condense the gases that are not reaching
Barium sulfate is an insoluble salt. Aqueous sodium the boiling point back to the flask. [1]
nitrate is soluble. Filtration is used to separate a This is the way to separate the mixture of gases,
mixture of solid and liquid. especially those with small differences in boiling
points.
2 (a) Simple distillation [1]
(b) Under the flask [1] 5 (a) Paper chromatography [1]
(c) Condenser [1] (b) 2 [1]
(d) To cool the water vapour [1] The 2 spots are not at the same positions as any
and turn into water [1] of the samples 1, 2, 3 and 4. [1]

(e) Heat [1] (c) Different solubilities of substances to the
Condense / cool [1] solvent used. [1]
or
(f) Water has a lower boiling point. [1] The attachment of substances to the paper. [1]
The substance with a lower boiling point evaporates
first. (d) (i) To check if food contains prohibited
colouring [1]
(g) Anhydrous copper(II) sulfate [1] or any correct usage
Change from white to blue [1]
or (ii) Some food colourings are harmful to
Anhydrous cobalt chloride [1] humans [1]
Change from blue to pink [1] or any correct explanation
3 (a) To ensure all acids react [1] 6 (a) Able to dissolve all the samples [1]
All acids need to be reacted to ensure the salt (b) Sample 3 [1]
obtained is pure and contains no acid after
crystallisation. (c) To visualise the spots / To detect the location of

(b) Filtration [1] spots [1]
Copper(II) oxide is a black solid. It can be separated (d) (i) Retention factor [1]
from the acid which is a liquid by filtration. 3.2

(c) Heat [1] (ii) 8.0 = 0.4 [2]
until the crystallisation point is reached or Note: 3.2 [1]; 0.4 [1]
crystals start to form. [1] 8.0

Answers 173

Answers.indd 173 3/4/22 3:54 PM