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Reaction with Metals

A yellow soli...

Question

A yellow solid known to be a single compound is completely insoluble in hot water dissolves in hot dilute $H C l$ to give an orange solution. When this solution is cooled, a white crystalline ppt is formed. This white precipitate redissolves on heating the solution. The compound is :

A

{F e (O H)}_{3}

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B

{P b C r O}_{4}

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C

K_{2} {C r O}_{4}

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D

{C o (O H)}_{2}

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Solution

The correct option is B ${P b C r O}_{4}$
The yellow solid is lead chromate $({P b C r O}_{4})$ . It is completely insoluble in hot water dissolves in hot dilute HCl to give an orange solution. In this reaction, the chromate ion is converted to dichromate ion which results in orange colour.
$2 C r O_{4}^{2 -} y e l l o w + 2 H C l \to C r_{2} O_{7}^{2 -} o r a n g e + H_{2} O$
When this solution is cooled, a white crystalline ppt is formed. This white ppt redissolves on heating the solution.
This is due to low solubility of lead dichromate in water.
Thus the compound is lead chromate $({P b C r O}_{4})$ .

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If true enter 1, else enter 0.

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