1.

What is the minimum volume of water required to dissolve 1 g of calcium sulphate at 298 K. K_(sp) for CaSO_(4) is 9.0xx10^(-6).

Answer»

2.45 L
4.08 L
4.90 L
3.00 L

Solution :`CaSO_(4)(s)+AQ hArr Ca^(2+)(aq)+SO_(4)^(2-)(aq)`
`K_(sp)=[Ca^(2+)][SO_(4)^(2-)]`
Suppose thesolubility of `CaSO_(4) = s "mol" L^(-1)`
`K_(sp)=sxxs=s^(2)`
`9.0xx10^(-6) = s^(2) or s=3xx10^(-3) "mol" L^(-1)`
Molar MASS of `CaSO_(4) = 40 + 32 + 64 = 136 g "mol" ^(-1)`
`:. 1g CaSO_(4) = (1)/(136) ` mol
`3xx10^(-3)` mol of `CaSO_(4)` require minimum WATER to dissolve = 1 L
`:. (1)/(136) ` molof `CaSO_(4)` will require water
`=(1)/(3xx10^(-3))xx(1)/(136) ~=2.45 L`


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