Question

In an aqueous solution of volume $500mL,$ when the reaction of $2A{g}^{+}+Cu\rightleftharpoons C{u}^{2+}+2Ag,$ reached equilibrium the $\left[C{u}^{2+}\right]$ was $xM$. When $500mL$ of water is further added, at the equilibrium $\left[C{u}^{2+}\right]$ will be

• A. 2 x M
• B. x M
• C. Between x M and x / 2 M
• D. Less than x / 2 M

Answer 1

Answer: (D)

$\underset{aM}{2A{g}^{+}}+Cu\rightleftharpoons \underset{xM}{C{u}^{2+}}+\underset{(V=500mL)}{2Ag}$

$K_c=\frac{\left[C{u}^{2+}\right]}{{\left[A{g}^{+}\right]}^2}=\frac{x}{a^2}$

Also $K_c=\frac{\left[C{u}^{2+}\right]}{{\left[A{g}^{+}\right]}^2}=\frac{\left[C{u}^{2+}\right]}{{\left(\frac{a}{2}\right)}^2}$ when $500mL$ is further added.

Thus to have $K_c$ constant $\left[C{u}^{2+}\right]$ must be less than $x/2$.