Chemistry 3 Nov/Dec 2007

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Chemistry Paper 3,Nov/Dec 2007

Questions:					1	2	3				Main

General Comments
Weakness/Remedies
Strength

Question 2

Aqueous solutions of two salts, ZnSO4 and CuCl2 are put into two separate beakers. Using the following reagents only, identify the ions present in the solutions. Give your answer in a tabular form.

Reagents:

NaOH(aq)
NH3(aq)
AgNO3(aq)
HNO3(aq)
BaCI2(aq)
HCI(aq)

_____________________________________________________________________________________________________

OBSERVATION

This question was attempted by only few candidates and the performance was poor. Most candidates did not attempt this question because they could not interpret the demand and for those who did, they failed to express their answers in a tabular form and sequentially; hence they lost marks. The answers required from candidates were as follows:

TEST

OBSERVATION

INFERENCE

ZnSO4aq) + NaOHaq) in drops +excess NaOH

ZnSO4aq) + NH3aq) in drops +excess NH3

ZnSO4aq) + BaCI2aq)
+ HCI

White gelatinous ppt
Ppt soluble in excess NaOH

White gelatinous ppt
Ppt soluble in excess NaOH

White ppt
Ppt undissolved/ ppt not soluble

Zn2+
Or

Zn 2+
confirmed

SO42- present

CuCI2aq) + NaOH(aq) in drops + excess NaOH

CuCI2(aq) + NH3(soln) in drops + excess NH3

CuCI2(aq) + AgNO3aq)
+ HNO3aq)

Blue ppt
Ppt undissolved/ppt not soluble

Blue ppt
Ppt dissolved to form deep blue solution

White ppt
Ppt insoluble in excess HNO3

Cu2+

Cu2+ confirmed

Cl-