Question

Q10.An aqueous solution contains 5.00x10-2 mol/L of Ca2+ and 7.00x10-3 mol/L of SO4

Answer 1

Answer:

The precipitate will form.

Explanation:

Let's write the equilibrium expression for the solubility product of calcium sulfate:

$CaSO_4(s)$ ⇄ $Ca^{2+}(aq)+SO_4^{2-}(aq)$

The solubility product is defined as the product of the free ions raised to the power of their coefficients, in this case:

$K_{sp}=[Ca^{2+}][SO_4^{2-}]=10^{-4.5}$

Our idea is to find the solubility quotient, Q, and compare it to the K value. A precipitate will only form if Q > K. If Q < K, the precipitate won't form. In this case:

$Q_{sp}=[Ca^{2+}][SO_4^{2-}]=5.00\cdot10^{-2} M\cdot7.00\cdot10^{-3} M=3.5\cdot10^{-4}$

Now given the K value of:

$K_{sp}=10^{-4.5}=3.2\cdot10^{-5}$

Notice that:

$Q_{sp}>K_{sp}$

This means the precipitate will form, as we have an excess of free ions and the equilibrium will shift towards the formation of a precipitate to decrease the amount of free ions.