Question 2A
C and D are inorganic salts. E is a solution of an organic compound. Carry out the following exercises on C, D and E. Record your observations and identify any gas(es) evolved. State the conclusion you draw from the result of each test.
(a)
To all of C, add about 2cm3 of distilled water in a boiling tube.
Shake to dissolve and test the solution with litmus paper.
(b)
(i) Test E with litmus paper.
(ii) Add all of E to the solution obtained in 2(a)
(c)
(i) Add about 5cm3 of distilled water to D in a test tube and
shake thoroughly. Divide the resulting solution into two portions.
(ii) To the first portion, add few drops of BaCl2(aq) followed by excess dil. HCl.
(iii) To the second portion, add NH3(aq) in drops and then in excess.
[21 marks]
Observation
The question was attempted by most candidates, and the performance was fairly good.
However, some of the candidates lost marks as result of non-adherence to rubrics, wrong observations and inferences.
The expected answers include:
|
Test |
Observation |
Inference |
(a) |
C(s) + H2O + litmus paper |
Red litmus paper turned blue |
Alkaline/Basicsolution |
(b)(i) |
E(aq) + litmus paper |
Blue litmus paper turned red |
Acidic solution |
(ii) |
E(aq) + C(aq)
|
Effervescence occurred |
CO2 from HCO3-/ CO32- |
(c) (i) |
D(s) + H2O |
D dissolved to give a colourless solution |
D is a soluble salt |
(ii) |
D(aq) + BaCl2(aq) + dil.HCl (excess) |
White precipitate Precipitate insoluble |
S2-SO32-, CO32- or SO42- SO42- present |
(iii) |
D(aq) + NH3(aq) in drops |
White gelatinous precipitate |
Zn2+ Al3+ |
|
then in excess |
Precipitate dissolved |
Zn2+ confirmed |