A one litre solution contains 0.04 M Na 2 HPO 4 and 0.02 M NaH 2 PO 4 . For H 3 PO 4 : P K a 1 = 2.14 ; P K a 2 = 6.84 ; P K a 3 = 12.3 The correct statement(s) is/are: (use:

Question

A one litre solution contains 0.04 M Na 2 ​ HPO 4 ​ and 0.02 M NaH 2 ​ PO 4 ​ . For H 3 ​ ​ PO 4 ​ : P K a 1 ​ ​ = 2.14 ; P K a 2 ​ ​ = 6.84 ; P K a 3 ​ ​ = 12.3 The correct statement(s) is/are: (use: l o g 2 = 0.3 ):

TestHub · Accepted Answer

pH HPO 4 2 − ​ + HCl t t pH f ​ 2 HPO 4 2 − ​ + H 2 ​ SO 4 ​ t t pH f ​ Δ pH HPO 4 2 − ​ + H + t t pH ​ = 6.84 + lo g 0.02 0.04 ​ = 7.14 → H 2 ​ PO 4 − ​ = 0 ​ 0.04 ​ 1 0 − 3 ​ 0.02 ​ = ∞ 0.039 0 0.021 = 6.84 + lo g 0.021 0.039 ​ ≃ pH i ​ → 2 H 2 ​ PO 4 − ​ = 0 0.04 0.01 0.02 = ∞ 0.02 0 0.04 = 6.84 + lo g 2 1 ​ ≃ 6.54 = − 0.6 → H 2 ​ PO 4 − ​ = 0 ​ 0.04 ​ 0.04 ​ 0.02 ​ = ∞ 0 0 0.06 = 2 pK a 1 ​ ​ + pK a 2 ​ ​ ​ = 4.49 ​

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