Question 2B
- F is a mixture of two inorganic salts. Carry out the following exercises on F.
Record your observations and identify any gas(es) evolved.
State the conclusions you draw from the results of each test.
- Put all of F into a boiling tube and add about 10 cm3 of distilled water. Stir well and filter. Keep both the filtrate and residue. Test the filtrate with litmus paper.
- To about 2 cm3 of the filtrate add few drops of BaCl2(aq) followed by dilute HCl.
- Put all the residue into a test tube and add 1 cm3 of dil HCl. Divide the resulting mixture into two.
- To the first portion of the mixture, add NaOH(aq) in drops and then in excess.
- To the second portion of the mixture, add NH3(aq) in drops and then in excess.
Observation
This question was popular among the candidates as majority of them responded to it.
In part (a), majority of the candidates were able to write the observations and inferences correctly.
In part (b), only few candidates were able to deduce the inferences.
In part (c), majority of the candidates wrote correct observations and inferences.
The expected answers include:
F = ZnCO3(s) + Na2SO4(s)
|
TEST |
OBSERVATION |
INFERENCE |
(a) |
F + water
Filtrate + litmus paper |
Partly soluble, No effect on either blue or red litmus paper |
filtrate is neutral |
(b) |
Filtrate + BaCl2(aq)
+ dil HCl |
White precipitate
Insoluble in HCl(aq)
|
CO32- , SO32- , SO42-, S2- SO42- |
(c) |
Residue + |
Effervescence occurred |
CO2 evolved from CO32-
|
(i) |
Solution from (c) + NaOH(aq) in drops then in excess |
White gelatinous precipitate
precipitate soluble |
Zn2+ /Al3+
Zn2+ / Al3+ |
(ii) |
Second portion of solution from (c) then in excess |
White gelatinous
Soluble in excess NH3(aq) |
Zn2+ ,Al3+ (both mentioned to score)
Zn2+ confirmed |