Question

Calculate the pH and the percentage of dissociation of hydrocyanic acid, knowing that the pKa of HCN is 9.2.

a) pH = 7.2, Dissociation = 15%
b) pH = 9.2, Dissociation = 50%
c) pH = 5.8, Dissociation = 10%
d) pH = 10.8, Dissociation = 75%

Answer 1

To calculate the pH and percentage of dissociation of hydrocyanic acid, use the pKa value and the formulas pH = pKa + log([A-]/[HA]) and % dissociation = ([A-]/[HA]) x 100. The correct answer is d) pH = 10.8, Dissociation = 75%.

Step-by-step explanation:

To calculate the pH and percentage of dissociation of hydrocyanic acid, we need to use the pKa value of HCN. The pKa value represents the equilibrium constant for the dissociation of the acid.

The pH can be calculated using the formula pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the acid's conjugate base and [HA] is the concentration of the acid.

The percentage of dissociation can be calculated using the formula % dissociation = ([A-]/[HA]) x 100.

By plugging in the given values into the formulas, we find that option d) pH = 10.8, Dissociation = 75% is the correct answer.