The Effect of NaCl Addition on Soap Chemical Equilibrium

Chemical Equilibrium of Soap Solution

Consider the chemical equilibrium of a soap that is present in its aqueous solution:

C17H35COONa(aq) C17H35COO–(aq) + Na+(aq)

sodium stearate (soap) stearate ion

What will happen if a large quantity of NaCl is added to the aqueous solution?

Effect of NaCl Addition

When a large quantity of NaCl is added to the aqueous solution, the equilibrium will shift to the left leading to the formation of more sodium stearate soap.

This is because the addition of NaCl will lead to an increase of Na+ ions. An increase of Na+ ions will shift the equilibrium to the left, favoring the formation of soap.