JEE Main Chemistry question

Excess of dilute sodium hydroxide solution is gradually added with shaking to an aqueous solution of zinc sulphate. What would you observe?

(A)A light blue precipitate is first formed which finally dissolves to give a deep blue solution
(B)A white precipitate appears which dissolves to give a colourless solutionCorrect
(C)A white precipitate is formed which does not dissolve
(D)No change takes place and the solution remains clear

Answer: (B)

Solution

Adding NaOH to solution first precipitates white, amphoteric : ZnSO_4+2NaOH \to Zn(OH)_2\downarrow+Na_2SO_4, and with excess NaOH this precipitate redissolves to give a colourless solution of sodium zincate: Zn(OH)_2+2NaOH \to Na_2ZnO_2+2H_2O. The

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Question ID VK-137821