Question

You mix 100. mL of 0.10 M HCI and 100. mL of 0.10 M NaCN. What is the pH of the resulting solution? Kₐ (HCN) = 4.0 times 10⁻¹⁰

a) 5.20
b) 5.35
c)6.20
d) 8.65
e) 8.80

Answer 1

To calculate the pH of the resulting solution, we need to consider the reaction between HCl and NaCN. This reaction produces HCN, which acts as a weak acid in the solution. We can calculate the concentration of HCN and use the equilibrium constant to find the concentration of H+ ions, allowing us to determine the pH. b) 5.35

Step-by-step explanation:

To calculate the pH of the resulting solution, we need to consider the reaction between HCl and NaCN.

1. HCl is a strong acid, so it will completely ionize in water to form H+ and Cl- ions.
2. NaCN is the salt of a weak acid, HCN. It will partially dissociate in water to form Na+ and CN- ions.
3. In the reaction between HCl and NaCN, H+ ions from HCl will react with CN- ions from NaCN to form HCN.
4. Since the reaction produces HCN, the resulting solution will act as a weak acid.
5. To calculate the pH, we need to calculate the concentration of HCN in the solution.
6. Using the concentrations and volumes provided, we can use the equation for the reaction: HCl + NaCN ⇌ HCN + NaCl.
7. Since the initial concentrations of HCl and NaCN are the same, the concentration of HCN will also be the same.
8. The equation for the dissociation of HCN is: HCN ⇌ H+ + CN-.
9. Since we know the equilibrium constant (Kₐ) for this dissociation reaction, we can calculate the concentration of H+ ions in the solution.
10. Finally, we can calculate the pH using the equation: pH = -log[H+].

Using this method, the pH of the resulting solution is around 5.35, so the correct answer is option b) 5.35.