Advertisements
Advertisements
Question
You are provided with PbCO3, ZnCO3 and CaCO3. How will you identify these cations?
Solution
By use of Ammonium hydroxide we can identify the ions PbCO3, ZnCO3 and CaCO3 as :
(i) \[\ce{PbCO3 + 2NH4OH -> Pb(OH)2 v + 2NH4NO3}\]
Pb(OH)2 forms white precipitate which are insoluble in excess ammonium hydroxide.
(ii) \[\ce{ZnCO3 + NH4OH -> Zn(OH)2 v + 2Na2CO3}\]
Zn(OH)2 forms white gelatinous precipitate which are soluble in excess ammonium hydroxide.
(iii) \[\ce{CaCO3 + NH4OH -> Ca(OH)2 + 2Na2CO3}\]
No precipitation of Ca(OH)2 occurs even with addition of excess of NH4OH. Because the concentration of hydroxide ion from ammonium hydroxide is so low that it cannot precipitate the hydroxide of calcium.
Concept Insight : Some precipitated metallic hydroxides by ammonium hydroxide become soluble hydroxides when treated with excess of ammonium hydroxide due to the formation of a soluble complex salt in the presence of excess of ammonium hydroxide.
APPEARS IN
RELATED QUESTIONS
Choose the correct answer from the options given below:
A chloride which forms a precipitate that is soluble in excess of ammonium hydroxide is:
1) Calcium chloride
2) Ferrous chloride
3) Ferric chloride
4) Copper chloride
What happens when ammonia solution is added first dropwise and then in excess to the following solution:
FeCl3
Write a balanced equation for this reaction.
How will you distinguish NH4OH solution from NaOH solution?
Write the observation, and balanced equation for the following reaction:
Ammonium hydroxide is added first in a small quantity, and then in excess, to a solution of copper sulphate.
Write the observation, and balanced equation for the following reaction:
Excess of ammonium hydroxide is added to a substance, obtained by adding hydrochloric acid to silver nitrate solution.
State two relevant observations of the following:
Ammonium hydroxide solution is added to zinc nitrate solution in minimum quantities and then in excess
The following table shows the tests a student performed on four different aqueous solutions which are X,Y,Z and W. Based on the observations provided, Identify the cation present
|
Chemical Test |
Observation | Conclusion |
| To Solution X, ammonium hydroxide is added in minium quantity first and then in excess | A dirty white precipitate is formed which dissolves in excess to form a clear solution | (i) |
| To Solution Y, ammonium hydroxide is added in minimum quantity first and then in excess | A pale blue precipitate is formed which dissolves in excess to form a clear inky blue solution | (ii) |
| To solution W, A small quantity of sodium hydroxide solution is added and then in excess | A white precipitate is formed which remains insoluble | (iii) |
| To a salt Z, calcium hydroxide solution is added and then heated | A pungent smelling gas turning moist red litmus paper blue is obtained | (iv) |
Write balanced equation :
Copper sulphate solution with ammonium hydroxide solution.
Rita was given an unknown salt for identification. She prepared a solution of the salt and divided it into two parts.
- To the first part of the salt solution, she added a few drops of ammonium hydroxide and obtained a reddish-brown precipitate.
- To the second part of the salt solution, she added a few drops of silver nitrate solution and obtained a white precipitate.
Name:
- The cation present and
- The anion present in the salt given for identification.
Write balanced equation:
Copper sulphate solution with ammonium hydroxide solution.
