the H+ Concentration in a 1.0 molar solution of HCN IS 2X10 -5 Oles/dm3.what is the value for Ka for HCN?

___________ HCN(aq) ___ ⇌ ___ H⁺(aq) ___ + ____ CN⁻(aq) ____ Ka
Initial: ____ 1.0 mol/dm³ ______ 0 mol/dm³ ________ 0 mol/dm³
Change: __ -y mol/dm³ ______ +y mol/dm³ _______ +y mol/dm³
At eqm: _ (1.0 - y) mol/dm³ ____ y mol/dm³ ________ y mol/dm³

At eqm:
[H⁺] = y mol/dm³ = 2 × 10⁻⁵ mol/dm³
y = 2 × 10⁻⁵

Ka = [H⁺] [CN⁻] / [HCN] = y² / (1.0 - y) = (2 × 10⁻⁵)² / [1.0 - (2 × 10⁻⁵)] = 4.0 × 10⁻¹⁰ (mol/dm³)