Question 2B
F is a double salt. Carry out the following exercises on F.
Record your observations and identify any gas(es) evolves.
State the conclusions you draw from the result of each test.
- Put all of F in a beaker and add about 10 cm3 of distilled water. Stir the resulting solution thoroughly. Test the solution with litmus paper.
- (i) To about 2 cm3 of the solution, BaCl2 solution followed by HCl(aq).
(ii) To another 2 cm3 portion of the solution, add NaOH(aq) in drops and then in excess. Heat the mixture.
(iii) To another 2 cm3 portion of the solution, add K2Fe(CN)6 solution.
[20 marks]
Observation
In part (a), majority of the candidates added distilled water to F and wrote correct observations.
In part (b), majority of the candidates wrote wrong observations and inferences.
The expected answers include:
|
TEST |
OBSERVATION |
INFERENCE |
(a) |
F+ distilled water + stirring F(aq) + litmus paper |
F dissolved to form a light green solution Turns blue litmus paper red |
Solution of F is acidic |
(b)(i) |
F(aq) + BaCl2(aq)
+ HCl(aq) |
White precipitate formed
Precipitate insoluble |
SO42-, SO32-, CO32-,
SO42- present |
(ii) |
F(aq) + NaOH(aq)in drops then in excess
|
Green (gelatinuous) precipitate formed. Precipitate insoluble in excess |
Fe2+
Fe2+
NH3(g) from NH4+ Fe3+ from Fe2+ |
(iii) |
F(aq) + K3Fe(CN)6(aq) |
Deep blue /colouration formed |
Fe2+ confirmed |