A sample of hard water contains 0.005 moles of calcium chloride per litre.What is the minimum concentration of sodium sulphate which must be added for removing the ` Ca^(2+) ` ions from this water sample ?
` K_(sp) " of " CaSO_4= 2.4 xx 10^(-5) `

Options

A. `4.8 xx 10^(-2)`
B. ` 4.8 xx 10^(-3)`
C. ` 2.4 xx 10^(-2)`
D. ` 2.4 xx 10^(-3)`

Answer

B

Explanation

`[Ca^(+2) ]= 5 xx 10 ^(-3) M`
From `K_(sp) " of " CaSO_4`
` 2.4 xx 10 ^(-5) = 5 xx 10^(-3) xx [SO_4 ^(-2) ]`
` [SO_4^(-2) ]= 4.8 xx 10 ^(-3) Mz`
` [Na_2 SO_4 ] =4.8 xx 10^(-3) M`