Question

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?

○ the equilibrium will shift to the right, favoring the dissociation of soap in aqueous solution
○ the equilibrium will shift to the left to such an extent that it leads to the precipitation of solid soap.
○ the equilibrium will not be affected by the addition of nacl to the solution.
○ the equilibrium will be permanently destroyed by the addition of nacl.

Explanation:

1. First, analyze the dissociation equilibrium of sodium stearate: $\ce{C_{17}H_{35}COONa(aq)

ightleftharpoons C_{17}H_{35}COO^{-}(aq) + Na^{+}(aq)}$.

1. When a large amount of $\ce{NaCl}$ is added, $\ce{NaCl}$ will dissociate into $\ce{Na^{+}}$ and $\ce{Cl^{-}}$ ions, increasing the concentration of $\ce{Na^{+}}$ ions in the solution.
2. According to Le Chatelier's principle, when the concentration of a product (here $\ce{Na^{+}}$) increases, the equilibrium will shift in the direction that reduces this concentration, i.e., the reverse reaction (to the left) is favored.
3. As the equilibrium shifts left, more undissociated sodium stearate (solid soap) will be formed, leading to precipitation.

Answer:

B. The equilibrium will shift to the left to such an extent that it leads to the precipitation of solid soap.