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ICSE Class 10 Chemistry Question 9 of 10

Analytical Chemistry — Question 7

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Question

Question 7

How will you distinguish calcium nitrate and zinc nitrate solution?

Answer

When ammonium hydroxide (NH4OH) is added to zinc nitrate solution [Zn(NO3)2], a gelatinous white ppt of zinc hydroxide [Zn(OH)2] is obtained which is soluble in excess of NH4OH.

ZnSO4colourless solution+2NH4OH⟶Zn(OH)2↓white gelatinous ppt+(NH4)2SO4colourless in solution\underset{\text{colourless solution}}{{\text{ZnSO}_4}} + 2\text{NH}_4\text{OH} \longrightarrow \underset{\text{white gelatinous ppt}}{\text{Zn(OH)}_2↓} + \underset{\text{colourless in solution}}{(\text{NH}_4)_2\text{SO}_4}

(With excess NH4OH ppt. dissolves)

Zn(OH)2+(NH4)2SO4+2NH4OH⟶[(Zn(NH3)4]SO4Tetraamminezinc (II) sulphate+4H2O\text{Zn(OH)}_2 + (\text{NH}_4)_2\text{SO}_4 + 2\text{NH}_4\text{OH} \longrightarrow \underset{\underset{\text{zinc (II) sulphate}}{\text{Tetraammine}}}{[(\text{Zn(NH}_3)_4]\text{SO}_4} + 4\text{H}_2\text{O}

On the other hand, calcium nitrate solution [Ca(NO3)2] does not give any ppt. even when excess of ammonium hydroxide is added.