pH of a Weak Acid SolutionCalculate the pH of a 1.39 mol.L–1 solution of hydrofluoric acid. The pKa of HF is 3.17.Enter your answer to 2 decimal places.

To calculate the pH of a weak acid solution, we can use the formula for the ionization of a weak acid HA ⇌ H+ + A- and the definition of the acid dissociation constant Ka.

Step 1: Write the ionization equation for the weak acid. HF ⇌ H+ + F-

Step 2: Write the expression for the acid dissociation constant Ka. Ka = [H+][F-]/[HF]

Step 3: Use the given pKa to find Ka. The relationship between Ka and pKa is Ka = 10^-pKa. So, Ka = 10^-3.17 = 0.000677

Step 4: Set up an ICE (Initial, Change, Equilibrium) table to find the equilibrium concentrations.

Initial: [HF] = 1.39 M, [H+] = 0, [F-] = 0 Change: [HF] = -x, [H+] = +x, [F-] = +x Equilibrium: [HF] = 1.39-x, [H+] = x, [F-] = x

Step 5: Substitute the equilibrium concentrations into the Ka expression and solve for x, which is the [H+].

0.000677 = x^2/(1.39-x)

Assuming x is much smaller than 1.39 (since HF is a weak acid and does not ionize completely), the equation simplifies to:

0.000677 = x^2/1.39

Solving for x gives x = sqrt(0.000677*1.39) = 0.031

Step 6: Calculate the pH using the formula pH = -log[H+].

pH = -log(0.031) = 1.51

So, the pH of the 1.39 M solution of hydrofluoric acid is approximately 1.51.