Page 62 - ACE YR IGCSE A TOP APPROACH TO CHEM

(iii) Sample 4 [1] Paper chromatography is used to identify amino
1.6 acids.
= 0.2
8.0 (d) Electrolysis [1]
Sample 2 [1] Lithium ions are separated by gaining an
4.8 electron to form lithium [1] at the cathode. [1]
= 0.6
8.0 [1]
7 (a) Draw 3 small circles on the chromatogram. [1] 9 (a) A substance that is composed of two or more
From the lowest to the highest: elements [1]
Yellow, red, blue with correct label [1] chemically combined [1]

(b) Water [1] (b) Must be in the correct order:
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The black ink is water-soluble (it is written in the 1 Dissolving [1]
statement). 2 Filtration [1]
(c) Different solubilities of substances to the 3 Evaporation / Crystallisation [1]
solvent used [1] (c) (i) Condenser [1]
The attachment of substances to the paper [1] Arrow pointing into lower aperture
(d) Draw a horizontal line below the baseline. [1] only [1]
The solvent level should not be above the baseline. Water should go in from the lower aperture.
If the solvent is above the baseline, substances (ii) The stopper is placed over the mouth of
cannot be separated properly.
fractionating column. [1]
(e) The pencil marking cannot dissolve in water. [1] Gases or vapour escape from the mouth of
fractionating column. [1]
(f) Spot the colour on the baseline. [1]
Let the solvent travel until the solvent front. [1] (iii) The mixture is flammable. [1]
Dry the chromatogram. [1] (iv) The temperature of the water bath cannot
8 (a) Add a dilute acid. [1] exceed 100°C. [1]
Filter. [1] Alcohols C and D have boiling points that
Copper does not react or dissolve. / Magnesium are higher than 100°C. [1]
reacts or dissolves, or forms salt. [1] 10 (a) (i) Zn / Zinc ions [1]
2+
Copper metal cannot react with dilute acid because
2+
–
it is not reactive. However, it can react with (ii) Zn + 2OH ➞ Zn(OH) [1]
2
concentrated acid. Magnesium reacts with dilute (b) (i) No reaction / No change [1]
acid.
(b) Diffusion (through a membrane) [1] (ii) A yellow precipitate is formed. [1]
Nitrogen diffuses faster than oxygen. [1] Silver iodide is a yellow solid.
because it has the smallest M . [1] (iii) AgI [1]
M N = 28; M O = 32 r 11 (a) A white [1]
2
r
2
r
or precipitate forms. [1]
Fractional distillation [1] It dissolves in excess of sodium hydroxide. [1]
The mixture of air is cooled and turns into a
+
liquid. [1] (b) NH [1]
4
Nitrogen with a lower boiling point than (c) A pale blue [1]
oxygen will tend to evaporate faster. [1] precipitate forms. [1]
Gases condense to become liquids. It dissolves in excess of ammonia solution [1]
or and turns into deep blue solution. [1]
Burn a named substance [1]
to produce non-gaseous products [1] (d) Add aqueous ammonia [1]
Oxygen reacts / nitrogen does not react. Name (e) Fe [1]
2+
the product of combustion. [1] –
Magnesium can be used. Magnesium burns and (f) Br [1]
reacts with oxygen to form magnesium oxide. (g) A white [1]
Magnesium oxide is a solid. Nitrogen does not react precipitate forms. [1]
with oxygen in the same way.
(h) Add dilute aqueous sodium hydroxide [1]
(c) Chromatography [1] and then some small pieces of aluminium
Use of locating agent / Two acids move at foil. [1]
different rates. / Leucine travels faster than Heat gently. [1]
histidine. / Leucine travels higher up on the
paper / further. [1]

Cambridge IGCSE TM
174 Ace Your Chemistry

Answers.indd 174 3/4/22 3:54 PM