Question 2
C is a mixture of two salts containing two cations and two anions.
The following tests were carried out on C. Complete the table.
|
TEST |
OBSERVATION |
INFERENCE |
(a) |
C + conc. H2SO4
Resulting solution warmed |
Colourless gas evolved which forms dense white fumes with NH3(g) brown fumes produced |
……………… ……………… |
(b)(i) |
Solution of C + NaOH(aq) in drops + excess
+ heat |
White gelatinous precipitate formed A colourless pungent smelling gas evolved which formed white dense fumes with conc. HCl
|
………………
……………… |
(ii) |
Solution of C + NH3(aq) in drops |
White precipitate formed. |
…………….. |
(iii) |
Solution of C + HNO3(aq) |
No precipitate, no gas evolved |
…………….. |
(iv) |
Solution of C + FeSO4(aq) +…………………………. |
Brown ring formed at the junction of the two layers |
NO3- confirmed |
(c) State the possible salts
[14 marks]
Observation
This question tested the knowledge of qualitative analysis. Majority of the candidates responded to this question and their performance was average.
In part (a), majority of the candidates could not write correct inferences to the test.
In part (b), majority of the candidates majority of the candidates did not write correct charges on ions when writing the inferences.
In part (c), majority of the candidates could not state the possible salt.
The expected answers include:
|
TEST |
OBSERVATION |
INFERENCE |
(a) |
C + conc H2SO4
Resulting solution warmed |
Colourless gas evolved which forms dense Brown fumes produced |
HCl gas
NO2 gas |
(b)(i)
|
Solution of C + + heat |
White gelatinous a colourless pungent smelling gas evolved |
Zn2+(l), Al3+
NH3 gas |
(ii) |
Solution of C + |
White precipitate formed precipitate soluble |
Zn2+ |
(iii) |
Solution of C +
+ AgNO3 |
No precipitate, no
White precipitate formed |
CO32- , SO32-, S2- absent (Any 2 for 2 marks / Cl- present |
(iv) |
Solution of C + |
Brown ring formed |
NO3- confirmed |
(c) Zn(NO3)2 and NH4Cl / ZnCl2 and NH4NO3