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Oxides and Oxoanions

A hydrated co...

Question

A hydrated colorless solid (A) is water soluble and finds use in medicine as a purgative. When a solution of (A) is treated with ammonium phosphate, a white precipitate is formed. (A) gives a pink mass in cobalt nitrate cavity test. What is (A) ?

A

F e S O_{4} .7 H_{2} 0

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B

N a_{2} S O_{4} . 10 H_{2}

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C

M g S O_{4} .7 H_{2} O

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D

C a S O_{4} .2 H_{2} 0

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Solution

The correct option is C $M g S O_{4} .7 H_{2} O$
MgSO $_{4}$ . 7H $_{2} O$ is a colorless water soluble solid used in medicine as purgative.
The reaction of MgSO $_{4}$ . + 7H $_{2} O$ with (NH $_{4}$ )PO $_{4}$ is given as:
MgSO $_{4}$ +(NH $_{4}$ ) $_{3}$ PO $_{4}$ $\to$ Mg $_{3}$ (PO) $_{4}$ $_{2}$ (white ppt) +(NH $_{4}$ ) $_{2}$ SO $_{4}$
And in cobalt nitrate cavity test:
2Co(NO $_{3}$ ) $_{2}$ $\to$ 2CO +4NO $_{2}$ +O $_{2}$
CoO +MgO $\to$ CoO.MgO (pink)

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