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Question
What do you observe when caustic soda solution is added to the following solution: first a little and then in excess
(a) FeCl3
(b) ZnSO4
(c) Pb(NO3)2
(d) CuSO4
(a) FeCl3
(b) ZnSO4
(c) Pb(NO3)2
(d) CuSO4
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Solution
The following observations have been made when caustic soda solution (NaOH) is added to the given salt solutions:
Salt solution
Addition of caustic soda
In little
In excess
Ferric chloride, FeCl3 (yellow solution)
Reddish brown precipitate of ferric hydroxide, Fe(OH)3.
Formed precipitate remains insoluble.
Ferrous sulphate, FeSO4 (pale green solution)
Dirty green precipitate of ferrous hydroxide, Fe(OH)2.
Formed precipitate remains insoluble.
Lead nitrate, Pb(NO3)2 (colourless solution)
White precipitate of lead hydroxide, Pb(OH)2.
The formed precipitate dissolves in excess sodium hydroxide and forms soluble complex salt, sodium plumbite, Na2PbO2.
Copper sulphate, CuSO4 (blue solution)
Pale blue precipitate of copper hydroxide, Cu(OH)2.
Formed precipitate remains insoluble.
| Salt solution | Addition of caustic soda | |
| In little | In excess | |
| Ferric chloride, FeCl3 (yellow solution) | Reddish brown precipitate of ferric hydroxide, Fe(OH)3. | Formed precipitate remains insoluble. |
| Ferrous sulphate, FeSO4 (pale green solution) | Dirty green precipitate of ferrous hydroxide, Fe(OH)2. | Formed precipitate remains insoluble. |
| Lead nitrate, Pb(NO3)2 (colourless solution) | White precipitate of lead hydroxide, Pb(OH)2. | The formed precipitate dissolves in excess sodium hydroxide and forms soluble complex salt, sodium plumbite, Na2PbO2. |
| Copper sulphate, CuSO4 (blue solution) | Pale blue precipitate of copper hydroxide, Cu(OH)2. | Formed precipitate remains insoluble. |
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