Question

A solution contains 1.25E-6 M Cu2+(aq) and 1.25E-6 M OH- (aq). Will a precipitate form? The Ksp for Copper (II) Hydroxide is 4.80E-20 M3.

Answer 1

Calculate Q and compare it to Ksp. First you need to know your reaction:

\[Cu(OH)_2 \space (s) \leftarrow \rightarrow Cu^{2+} \space (aq) + 2 OH^- \space (aq)\]
Now we can calculate Q:
\[Q=[Cu^{2+}][OH^-]^2\]\[Q=(1.25 \times 10^{-6})(1.25 \times 10^{-6})^2\]\[Q=1.95 \times 10^{-18}\]
In this case, Q > Ksp. That means the reverse reaction will be favored and a precipitate will form, in order to decrease the concentration of products and ultimately make Q=Ksp!

Answer 2

Thank you!