Topic 9 Detection and Analysis
Topic 9 Detection and Analysis
Section D Short Questions
1
Oxidizing ethanol to ethanoic acid / Set0up Y / The water supply should enter the condenser at the lower opening and leave at the upper opening to get a better cooling effect.
Separating the colourings in chocolate bean coating / Set-up X / The level of colour sample spots should be higher than that of the solvent in the beaker. Otherwise, the colour samples would dissolve in the solvent.
Collecting sulphur dioxide during its preparation / Set-up Y / Sulphur dioxide is soluble in water. It should not be collected by displacement of water. It can be collected by downward delivery because it is denser than air.
2 a) · Shake the solid mixture with water. Copper(II) oxide is insoluble in water while
copper(II) sulphate is soluble.
· Obtain copper(II) oxide from the mixture by filtration.
b) · Add dilute hydrochloric acid (or dilute sulphuric acid) to the mixture. Zinc reacts with
the acid while copper does not. Add acid until there is no gas bubbles given off. Zinc
has reacted with all the acid.
· Obtain copper from the mixture by filtration.
c) · Shake the mixture with water. Sodium carbonate is soluble in water while sand is
insoluble.
· Remove the sand from the mixture by filtration.
· Heat the filtrate (i.e. sodium carbonate solution) to remove some of the water.
· Allow the hot and concentrated filtrate to cool to obtain crystals.
3 a) Lysine, leusine and valine
b) Protein X contains lysine, valine and an unknown amino acid.
From the chromatogram, it can be concluded that three amino acids are present in
X. One of the amino acids travels the same distance as lysine while another amino acid
travels the same distance as valine. Therefore it can be concluded that X contains these
two amino acids. Besides that, there is one amino acid in X that travels a distance
different from all the three known amino acids. Therefore there is one unknown amino
acid in X.
4
5
Aluminium hydroxide / Insoluble
Ammonium carbonate / Soluble
Barium sulphate / Insoluble
Calcium nitrate / Soluble
Copper(II) carbonate / Insoluble
Iron(II) chloride / Soluble
Iron(III) sulphate / Soluble
Lead(II) bromide / Insoluble
Magnesium oxide / Insoluble
Potassium sulphite / Soluble
Silver iodide / Insoluble
Zinc chloride / Soluble
6
Carbonate ion / Limewater / Limewater turns milky / Carbon dioxide
Hypochlorite ion / Moist blue litmus paper / Moist blue litmus paper turns red and then white / Chlorine
Sulphite ion / Filter paper moistened with acidified potassium dichromate solution / Moistened filter paper turns from orange to green / Sulphur dioxide
7 a) Dissolve each solid in water. Add dilute nitric acid, followed by silver nitrate solution to
each solution. Solution of sodium chloride gives a white precipitate while solution of
sodium bromide gives a cream precipitate.
b) Dissolve each solid in water. Add dilute sodium hydroxide solution to each solution.
Solution of iron(II) sulphate gives a green precipitate while solution of copper(II)
sulphate gives a blue precipitate.
c) Dissolve each solid in water. Add dilute sodium hydroxide solution to each solution.
Solution of calcium nitrate gives a white precipitate which is insoluble in excess dilute
sodium hydroxide solution. Solution of aluminium nitrate gives a white precipitate which
is soluble in excess dilute sodium hydroxide solution.
d) Add dilute hydrochloric acid to both solids. Copper(II) carbonate gives gas bubbles with
the acid while copper(II) chloride shows no reaction.
e) Add water to both solids. Zinc sulphate is soluble in water while lead(II) sulphate is
insoluble.
f) Warm each solid with calcium hydroxide solution. Ammonium chloride gives a gas that
turns moist red litmus paper blue while potassium chloride does not.
g) Add each acid to zinc. Dilute sulphuric acid and zinc give a gas which gives a ‘pop’
sound with a burning splint. Dilute nitric acid and zinc give a gas which turns brown
when mixed with air.
h) Conduct flame test on each solid. Sodium sulphate gives a golden yellow flame while
sugar does not.
i) Add each acid to copper. Concentrated sulphuric acid and copper give a gas. The gas
turns filter paper moistened with acidified potassium dichromate solution from orange to
green. There is no reaction between dilute sulphuric acid and copper.