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For the precipitation of cations of grou...

For the precipitation of cations of group four in the qualitative analysis, the medium is made alkaline before passing `H_(2)S` gas. The purpose of alkaline solution is

A

to supress the ionisation of `H_(2)S`

B

to increase the ionisation of `H_(2)S`

C

to increase the ionisation of metal salt

D

to decrease the ionisation of metal salt.

Text Solution

Verified by Experts

The correct Answer is:
B
`H_(2)S hArr 2H^(+) +S^(-2)`
`NH_(4)OH rarr NH_(4)^(+) +OH^(-)`
`H^(+)` combines with `OH^(-)` to form water and thus the first equilibrium shifts in the forward direction to increase the ionisation of `H_(2)S`.
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Knowledge Check

  • H_2 S is used for precipitation of cations of

    A
    2nd group
    B
    2nd and 4th group
    C
    3rd and 4th group
    D
    4th and 5th group

  • In the precipitation of the iron group in qualitative analysis, ammonium chloride is added before adding ammonium hydroxide to

    A
    decrease concentration of `OH^(-)` ions.
    B
    prevent interference by phosphate ions.
    C
    increase concentration of `Cl^(-)` ions.
    D
    increase concentration of `NH_(4)^(-)` ions.

  • In the precipitation of the iron group in qualitative analysis, amonium chloride is added before adding ammonium hydroxide to

    A
    Decrease concentration of `OH^(-)` ions
    B
    Prevent interference by phosphate ions
    C
    Increase concentration of `Cl^(-)` ions
    D
    Increase concentration of `NH_(4)^(+)` ions

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