# How do you calculate percent dissociation?

Mar 12, 2014

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%