A solution contains `Pb^(+ 2)`ion. In order to precipitate `Pb^(+2 )` ions, sodium sulphate solution is required to be added. What is the concentration of sulphate ion required to reduce the concentration of `Pb ^(+2)` to `2 xx 10^(-6 )` mole per litre ? (`K_(sp)` for` PbSO_(4) = 1.8 xx 10^(-8)`)

Options

A. `5 xx 10 ^(-3) M`
B. `4 xx 10 ^(-3) M`
C. `9 xx 10 ^(-3) M`
D. `6 xx 10 ^(-3) M`

Answer

C

Explanation

The concentration of sulphate ion required is determined as follows
`K _(sp ) = [Pb ^(+2) ] [ SO _(4) ^( -2) ]`
`1.8 xx 10 ^(-8) = 2 xx 10 ^(-6) xx [ SO _(4) ^(-2) ]`
`[SO _(4) ^(-2) ] = 9 xx 10 ^(-3) M`