Question 2A
C and D are inorganic salts. Carry out the following exercises on them. Record your observations and identify any gas(es) evolved. State the conclusions you draw from the result of each test.
(a) Put all of C in a test tube and add about 5 cm3 of distilled water. Shake thoroughly and test the resulting solution with litmus paper. Divide the solution into three portions
- To the first portion, add NaOH (aq) in drops, then in excess.
- To the second portion, add NH3 (aq) in drops, then in excess.
- To the third portion, add AgNO3 (aq) followed by HCl (aq).
(b)(i) Put all of D in a test tube and add about 5 cm3 of distilled water. Shake thoroughly and feel the test tube.
(ii) To about 2 cm3 of the solution add HCl (aq)
[23 marks]
Observation
In part (a), majority of the candidates could not correctly deduce inferences from the observations. They wrote wrong cations.
In part (b), majority of the candidates did not write their observations when they felt the test tube.
The expected answers include:
|
TEST |
OBSERVATION |
INFERENCE |
(a) |
C+ distilled water +shaking Resulting solution + litmus paper |
C dissolved to form a Solution turns blue litmus paper red |
Solution is acidic |
(i) |
1st portion + NaOH(aq) in drops then in excess |
Blue precipitate
Precipitate insoluble in excess |
Cu2+ present |
(ii) |
2nd portion + NH3(aq) in drops then in excess |
(Light) blue precipitate Precipitate dissolves in excess to form a deep blue solution |
Cu2+ confirmed |
(iii) |
3rd portion + AgNO3(aq)
+ HCl(aq) |
White precipitate formed
Precipitate insoluble |
Cl-or CO32- Cl- present |
(b)(i) |
D + distilled water
touching/feel |
D dissolved to form a colourless solution Test tube feels cold on touching |
dissolution is |
(ii) |
D(aq) + HCl(aq) |
Effervescence a colourless odourless gas evolved. Gas turned lime |
CO2 from |