Question

1. write the balanced chemical equation and the kₑ expression for the following reactions or processes that occur in water:

a. copper metal reacts in a solution of silver ions to produce a blue solution of copper(ii) ions and silver metal.
b. when added to water, ammonia will undergo hydrolysis to form the ammonium cation and hydroxide anion.
c. lead metal will react in a solution of chromium(iii) ions to form lead(ii) ions and chromium (ii) ions.
d. only a small amount of barium carbonate will dissolve in water.

Explanation:

Step1: Write balanced equation for a

Copper (Cu) reacts with silver ions ($Ag^+$) to form copper(II) ions ($Cu^{2 +}$) and silver (Ag). Balance by electrons:

$$Cu(s)+2Ag^+(aq) ightleftharpoons Cu^{2 +}(aq)+2Ag(s)$$

Step2: Write $K_c$ expression for a

The $K_c$ expression for a reaction $aA + bB
ightleftharpoons cC + dD$ is $K_c=\frac{[C]^c[D]^d}{[A]^a[B]^b}$. Solids are not included in $K_c$ expressions. So for the above reaction, $K_c=\frac{[Cu^{2 +}]}{[Ag^+]^2}$

Step3: Write balanced equation for b

Ammonia ($NH_3$) reacts with water ($H_2O$) to form ammonium ion ($NH_4^+$) and hydroxide ion ($OH^-$).

$$NH_3(aq)+H_2O(l) ightleftharpoons NH_4^+(aq)+OH^-(aq)$$

Step4: Write $K_c$ expression for b

Since water is a pure liquid and not included in the $K_c$ expression, $K_c = [NH_4^+][OH^-]/[NH_3]$

Step5: Write balanced equation for c

Lead (Pb) reacts with chromium(III) ions ($Cr^{3+}$) to form lead(II) ions ($Pb^{2+}$) and chromium(II) ions ($Cr^{2+}$). Balance by electrons:

$$3Pb(s)+2Cr^{3+}(aq) ightleftharpoons 3Pb^{2+}(aq)+2Cr^{2+}(aq)$$

Step6: Write $K_c$ expression for c

Solids are excluded from $K_c$ expressions. So $K_c=\frac{[Pb^{2+}]^3[Cr^{2+}]^2}{[Cr^{3+}]^2}$

Step7: Write balanced equation for d

Barium carbonate ($BaCO_3$) dissolves in water to form barium ions ($Ba^{2+}$) and carbonate ions ($CO_3^{2 -}$).

$$BaCO_3(s) ightleftharpoons Ba^{2+}(aq)+CO_3^{2 -}(aq)$$

Step8: Write $K_c$ expression for d

Excluding the solid, $K_c=[Ba^{2+}][CO_3^{2 -}]$

Answer:

a. Balanced equation: $Cu(s)+2Ag^+(aq)
ightleftharpoons Cu^{2 +}(aq)+2Ag(s)$; $K_c=\frac{[Cu^{2 +}]}{[Ag^+]^2}$
b. Balanced equation: $NH_3(aq)+H_2O(l)
ightleftharpoons NH_4^+(aq)+OH^-(aq)$; $K_c = \frac{[NH_4^+][OH^-]}{[NH_3]}$
c. Balanced equation: $3Pb(s)+2Cr^{3+}(aq)
ightleftharpoons 3Pb^{2+}(aq)+2Cr^{2+}(aq)$; $K_c=\frac{[Pb^{2+}]^3[Cr^{2+}]^2}{[Cr^{3+}]^2}$
d. Balanced equation: $BaCO_3(s)
ightleftharpoons Ba^{2+}(aq)+CO_3^{2 -}(aq)$; $K_c=[Ba^{2+}][CO_3^{2 -}]$