A weak electrolyte AB2 dissociates as AB2 A^2+ + 2B- with degree of dissociation alpha. The van't Hoff factor is

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A weak electrolyte $AB X_{2}$ dissociates as $AB X_{2} A X^{2 +} + 2 B X^{-}$ with degree of dissociation $α$ . The van't Hoff factor is

Start with 1 mol: after dissociation there are

(1 - α)

AB X_{2}

α

A X^{2 +}

and

2 α

B X^{-}

, totalling

1 + 2 α

. Since

i

is total moles after/before,

i = 1 + 2 α