Which of the following statements is not true ?

Options

A. On passing `H_(2)S` through acidified acidified `K_(2)Cr_(2)O_(7)` solution, a milky colour is observed
B. `Na_(2)Cr_(2)O_(7)` is preferred over `K_(2)Cr_(2)O_(7)` in volumetric anlysis
C. `K_(2)Cr_(2)O_(7)` solution in acidic medum is orange
D. `K_(2)Cr_(2)O_(7)` solution because yellow on increasing the pH beyond 7

Answer

B

Explanation

Sodium dichromate `(Na_(2)Cr_(2)O_(7))` can't be used in volumetric analysis because it is hygroscopic in nature. On passing `H_(2)` through acidifield `K_(2) Cr_(2)O_(7)` solution, a milky colour is observed due to the formation of sulphur:
`K_(2)Cr_(2)O_(7) + 4H_(2)SO_(4) + 3H_(2)S rarr K_(2)SO_(4) + Cr_(2)(SO_(4))_(3) + 7H_(2)O + 3S`
Both dichromate and chromate ions are in equilibrium:
`underset("Orange")(Cr_(2)O_(7)^(2-))+H_(2)O hArr 2 underset("Yellow")(CrO_(4)^(2-))+2H^(+)`
In alkaline solution, chromate ions predominate while in acidic olution, dichromate ions are present.