Find pH and concentration?

2017-12-30 2:56 pm
Calculate the pH and concentration of sulfite (SO3^-2) ions of a 0.01 M solution of H2SO3

Ka1= 1.7x10^-2
Ka2= 6.4x10^-8

回答 (1)

2017-12-30 8:57 pm
Consider the first dissociation of H₂SO₃ :
____________ H₂SO₃(aq) __ ⇌ __ HSO₃⁻(aq) __ + __ H⁺(aq) ___ Kₐ₁ = 1.7 × 10⁻²
Initial: _______ 0.01 M _________ 0 M __________ 0 M
Change: ______ -y M __________ +y M _________ +y M
At eqm: ____ (0.01 - y) M _______ y M ___________ y M

As Kₐ₂ ≪ Kₐ₁ and Kₐ₂ is very small, the changes of [HSO₃⁻] and [H⁺] in the second dissociation is negligible.

Consider the second dissociation of H₂SO₃ :
__________ HSO₃⁻(aq) __ ⇌ __ SO₃²⁻(aq) __ + __ H⁺(aq) ___ Kₐ₂ = 6.4 × 10⁻⁸
At eqm: _____ y M ___________ ? M __________ y M

Kₐ₂ = [SO₃²⁻] [H⁺] / [HSO₃⁻]
6.4 × 10⁻⁸ = [SO₃²⁻] y / y
[SO₃²⁻] = 6.4 × 10⁻⁸ M


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