A diprotic acid H2A has pK_a1 = 3.0 and pK_a2 = 7.0. Select the correct statement(s).

A solution of the pure salt NaHA has pH approx 5.0

At pH = 7.0, less than 0.01% of the total acid is H2A

A solution of the pure salt NaHA has pH approx 5.0

At pH = 5.0 the average charge per acid molecule is -1.5

At pH = 7.0, less than 0.01% of the total acid is H2A

JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ia201

A diprotic acid $H X_{2} A$ has $p K_{a 1} = 3.0$ and $p K_{a 2} = 7.0$ . Select the correct statement(s).

pH (NaHA) = (3.0 + 7.0) /2 = 5.0

. At

pH = 5

[H X_{2} A] / [HA X^{-}] = 1 0^{- 2} = [A X^{2 -}] / [HA X^{-}]

, so

[H X_{2} A] = [A X^{2 -}]

. At

pH = 7.0

the fraction of

H X_{2} A

5.0 \times 1 0^{- 5}

, below

1 0^{- 4}

. At

pH = 5

almost all is

HA X^{-}

, so the average charge is close to

- 1

, not

- 1.5