Acid Equilibrium Problem: Determining Hydrogen Ion Concentration

How can we find the concentration of hydrogen ions in a solution of butanoic acid and NaCl?

Given data: concentration of butanoic acid = 45.0 mM, concentration of NaCl = 0.1 M, ionization constant of butanoic acid (Ka) = 1.52×10−5.

Answer:

The concentration of hydrogen ions in a solution of 45.0 mM butanoic acid and 0.1 M NaCl can be determined using the equilibrium table method.

To solve this problem, we can set up an equilibrium table for the dissociation of butanoic acid (C3H7COOH) into H+ and C3H7COO-. The equilibrium expression can be solved for the concentration of H+ ions.

The initial conditions include 45.0 mM butanoic acid with no H+ or C3H7COO-. Denote the equilibrium concentration of H+ as 'x'. The equilibrium expression for the reaction is Ka = [H+][C3H7COO-]/[C3H7COOH] = x*x/(45.0-x).

Solving the equation for x will give us the concentration of H+ ions, which can be compared to the provided options (A-D). The presence of NaCl salt may affect activity coefficients but can be ignored for this question.