Question

How do you calculate percent dissociation?

Answer 1

Divide the mass of dissociated ions by the total mass of dissociated and undissociated species; then multiply by 100 percent.

You can do this by moles, too, if you use the proper coefficients from the balanced reaction.

Example: When 0.5 mol of acetic acid is dissolved in enough water to make 1 liter of solution, the measured pH is 2.5. What is the percent dissociation of the acid?

Concentration of ionized acid = `10^(-2.5)` M = 3.2 x `10^(-3)` M
Concentration of undissociated acid = 0.497 M
Percent dissociated = 3.2 x `10^(-3)` M / 0.5 M * 100% = 0.64%