Question

Explain using Lechatelier’s Principle:

The solution became cloudy and solid formed at base after adding 0.5 ML concentrated HCl (12M) to about 5 ML of saturated NaCl solution.

Answer 1

The Equilibrium reaction

NaCl(s) = Na+(aq) + Cl-(aq)

Equilibrium constant expression of the reaction

K = [Na+ ] [Cl-]

For saturated solution of NaCl

Rate of forward reaction = Rate of reverse reaction

For the solution is less than saturated

Rate of forward reaction > Rate of reverse reaction

For supersaturated solution

Rate of forward reaction < Rate of reverse reaction

Now add 0.5 mL concentrated HCl (12M) into saturated NaCl

Cl- ions will increase.

According to Lechatelier’s Principle:

To counteract the formation of more Cl- ions. The reaction will proceed towards NaCl in the reverse direction and more solid NaCl (white precipitate) occurs.