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ICSE Class 9 Chemistry Question 7 of 18

Chemical Changes & Reactions — Question 15

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Question 15

Explain with the help of balanced equations, how precipitation reactions are used for identifying the positive radicals in three different salts, each having a different cation [positive ion].

Answer

Precipitation reactions finds it's use in analytical chemistry for identifying the positive radical in a salt by analyzing the colour of the precipitate.

(i) FeSO4 + 2NaOH ⟶ Na2SO4 + Fe(OH)2 ↓

Identified ion: Fe2+ ; Dirty green ppt. of Iron [II] hydroxide is obtained. Hence, it can be identified.

(ii) CuSO4 + 2NaOH ⟶ Na2SO4 + Cu(OH)2 ↓

Identified ion: Cu2+ ; Pale blue ppt. of Copper [II] hydroxide is obtained. Hence, it can be identified.

(iii) Pb(NO3)2 + 2NaOH ⟶ 2NaNO3 + Pb(OH)2 ↓

Identified ion: Pb2+ ; Chalky white ppt. of Lead [II] hydroxide is obtained. Hence, it can be identified.