Question

For a weak acid in an aqueous solution, what is the difference between the actual [HA] and the formal [HA]? (symbolized as F

Answer 1

suppose HA is the weak acid . HA can be dissociated into H+ and A- . there will be equilibrium estabilised between weak acid undissociated part and dissociated ions

suppose if intial concentration of HA is C . here HA is known to be formal HA ( initial )

once equilibrium is established some of the concentration decreases from ' C' . so the resulatant conentration = C- x

here weak acid is called actual acid . because the actual amount contributed can by known from here only

HA < ---------------------------> H+ + A-

C 0 0 -----------------------> initial

-x +x +x ------------------------> change

C-x x x ----------------------------> equailbrium

formal concentration = [HA] = C

actual concetration = [HA] = C- x