Page |1
Analytical Chemistry (Use of NaOH and
NH4OH)
Q.1. Using Sodium hydroxide solution, how would you distinguish :
i.
ii.
iii.
Zinc nitrate (or sulphate)solution and Calcium nitrate solution?
Iron (II) chloride from Iron (III) chloride?
Lead hydroxide from Magnesium hydroxide?
Ans.: i.
Zinc nitrate (or sulphate)
Calcium nitrate
When Sodium hydroxide solution is
added a white precipitate is formed
which is soluble in excess of sodium
hydroxide.
When Sodium hydroxide solution is
added a white precipitate is formed
which is insoluble in excess of Sodium
hydroxide.
Iron (II) chloride
Iron (III) chloride
When sodium hydroxide is added, dirty
green precipitate is formed which
changes to reddish brown after some
time.
When sodium hydroxide solution is
added, a reddish brown precipitate is
formed.
Lead hydroxide
Magnesium hydroxide
When sodium hydroxide is added, lead
hydroxide is dissolved in it.
When sodium hydroxide is added, there
is no visible reaction i.e. it remains
insoluble.
ii.
iii.
iv.
Q.2.
i.
ii.
Sodium hydroxide solution is added to solution A. A white precipitate is formed which is
insoluble in excess of Sodium hydroxide solution. What is the metal ion present in
solution A?
When Ammonium hydroxide solution is added to solution B a pale blue precipitate is
formed. This pale blue precipitate dissolves in excess of Ammonium hydroxide giving an
inky blue solution. What is the cation present in solution B? What is the probable colour of
solution B?
Page |2
Ans.: i.
ii.
Calcium ion [Ca2+]
Copper ion [Cu2+]. The colour of solution ‘B’ is blue.
Q.3. You are given the three white powders Calcium carbonate, Lead carbonate and Zinc
carbonate. Describe the tests you would carry out in solution to identify the metal in each of the
above compounds. Indicate clearly how you would prepare the solutions for the tests.
Ans.:
Calcium carbonate
Lead carbonate
Zinc carbonate
Calcium carbonate is
dissolved in dilute Nitric
acid and then Ammonium
hydroxide is added to it. No
visible reaction is seen.
Lead carbonate is
dissolved in dilute Nitric
acid and then Ammonium
hydroxide is added to it. A
white precipitate is formed
which is insoluble in
excess.
Zinc carbonate is
dissolved in dilute Nitric
acid and then
Ammonium hydroxide is
added to it. A white
precipitate is formed
which is soluble in
excess.
Q.4. Write an equation for the following reaction : Copper sulphate solution is added to Sodium
hydroxide solution.
Ans.:
CuSO4 + 2NaOH → Cu(OH)2 + Na2SO4.
Q.5. Three test-tubes contain Calcium nitrate solution, Zinc nitrate solution and Lead nitrate
solution respectively. Each solution is divided into two portions (i) and (ii). Describe the effect of :
i.
ii.
Adding Sodium hydroxide to each portion in turn till it is in excess.
Adding Ammonium hydroxide to each portion in turn till it is in excess.
Ans.:
i.
Sodium Hydroxide
Small amount
In excess
Calcium nitrate
White precipitate
Insoluble
Zinc nitrate
White precipitate
Soluble
Lead nitrate
White precipitate
Soluble
ii.
iii.
Ammonium Hydroxide
Page |3
Small amount
In excess
Calcium nitrate
No visible reaction
No change
Zinc nitrate
White precipitate
Soluble
Lead nitrate
White precipitate
Insoluble
Q.6. State what do you observe when : Ammonium hydroxide is added to Iron (III) sulphate
solution.
Ans.:
A reddish brown precipitate is formed.
Q.7. The following table shows the tests a student performed two aqueous solutions A and B.
Write down the observations (i) and (ii) that were made.
Test
Observation Conclusion
(i) To solution A, Sodium
hydroxide solution was added.
(i)
A contains Fe3+ ions
(ii) To solution B, Ammonium
hydroxide solution was added
slowly till in excess.
(ii)
B contains Cu3+ ions
Ans.:
i.
ii.
Reddish brown coloured precipitate is appeared.
A pale blue or bluish white precipitate is formed which dissolves in excess of Ammonium
hydroxide and give deep blue / intense blue / inky blue solution.
Q.8. How would you distinguish between Zn 2+ and Pb2+ using ammonium hydroxide solution?
Ans.:
Zn2+
Pb2+
On adding NH4OH drop by drop to a
solution of Zinc salt a white precipitate is
formed which is soluble in excess of
NH4OH.
On adding NH4OH drop by drop to a
solution of lead salt a white precipitate is
formed which is insoluble in excess of
NH4OH.