Question

What is the fluoride ion concentration for a saturated solution of BaF 2 if the K sp for BaF 2 is 1.8 × 10 -7 ?

Answer 1

`\\ \rm\rightarrowtail BaF_2\longrightarrow Ba^(2+)+2F-`

• BaF_2 be x
• Ba2+ is also x
• F- is 2x

Now

`\\ \rm\Rrightarrow K_(sp)=[Ba^2+][F-]^2`

`\\ \rm\Rrightarrow 1.8* 10^(-7)=x(2x)^2`

`\\ \rm\Rrightarrow 4x^3=1.8* 10^(-7)`

`\\ \rm\Rrightarrow x^3=0.45* 10^(-7)`

`\\ \rm\Rrightarrow x=\sqrt[3]{0.000000045}`

`\\ \rm\Rrightarrow x=0.00376M`

`\\ \rm\Rrightarrow x=3.8* 10^(-3)M`

So

`\\ \rm\Rrightarrow [F-]=2x=7.6* 10^(-3)M`