Question

1. What is the pH of a 0.15 M solution of HClO? K_a for HClO = 3.5 x 10^-8  

1. The value of K_a for the weak acid Benzoic acid (C₆H₆COOH) is 1.5 × 10^-5. What are the equilibrium concentrations of all species if 1.50 g of Benzoic acid is dissolved in enough water to make a 250.0 mL solution? What is the pH of the solution?

3. Ammonium ion is the conjugate acid of Ammonia.   What is the pH of a 0.25 M solution of NH₄Cl?   The K­_b for Ammonia, NH₃, is 1.8 × 10^-5.

Steps:

1. What is the balanced chemical reaction?
2. Set up Ka expression:
3. Determine the value of K_a for the conjugate acid from the K_b given
4. Determine the initial concentrations of each species present:
5. Set up table:

initial concentration (M)
change in conc (M)
equilibrium conc (M)

6. Solve for Q to determine the direction of the reaction:
7. Solve for the equilibrium concentrations in terms of x:
8. Solve for x: (Can you make the assumption that x is small compared to the initial concentrations?)
9. Determine the % reaction to verify assumption if made:
10. Check your equilibrium concentrations in Ka to determine if answers are correct.
11. Calculate pH from the equilibrium concentration of H₃O⁺

Answer 1