The P Block Elements - Result Question 79
####82. A certain compound $(X)$ when treated with copper sulphate solution yields a brown precipitate. On adding hypo solution, the precipitate turns white. The compound is [1994]
(a) $K_2 CO_3$
(c) $KBr$
(b) $KI$
(d) $K_3 PO_4$
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Solution:
- (b) $KI$ reacts with $CuSO_4$ solution to produce cuprous iodide (white precipitate) and $I_2$ (which gives brown colour). Iodine reacts with hypo $(Na_2 S_2 O_3 .5 H_2 O)$ solution. Decolourisation of solution shows the appearance of white precipitate.
$ \begin{aligned} & 2 Na_2 S_2 O_3+I_2 \longrightarrow \underset{\begin{matrix} \text{ Sod. tetra } \\ \text{ thionate } \\ \text{ (colourless) } \end{matrix} }{Na_2 S_4 O_6+2 NaI} \end{aligned} $
