Ka for hcn is 4.9 ⋅ 10-10. what is the ph of a 0.068 m aqueous solution of sodium cyanide? ka for hcn is 4.9 10-10. what is the ph of a 0.068 m aqueous solution of sodium cyanide? 0.74 7.00 2.96 13.24 11.07

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Chemistry

Dexter

24 July, 17:57

Ka for hcn is 4.9 ⋅ 10-10. what is the ph of a 0.068 m aqueous solution of sodium cyanide? ka for hcn is 4.9 10-10. what is the ph of a 0.068 m aqueous solution of sodium cyanide? 0.74 7.00 2.96 13.24 11.07

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Cookie Dough · Answer 1

Answer is: pH of solution of sodium cyanide is 11.07.

Chemical reaction 1: NaCN (aq) → CN ⁻ (aq) + Na⁺ (aq).

Chemical reaction 2: CN ⁻ + H₂O (l) ⇄ HCN (aq) + OH⁻ (aq).

c (NaCN) = c (CN ⁻) = 0.068 M.

Ka (HCN) = 4.9·10⁻¹⁰.

Kb (CN ⁻) = 10⁻¹⁴ : 4.9·10⁻¹⁰ = 2.04·10⁻⁵.

Kb = [HCN] · [OH ⁻] / [CN⁻ ].

[HCN] · [OH ⁻] = x.

[CN ⁻] = 0.068 M - x ...

2.04·10 ⁻⁵ = x² / (0.068 M - x).

Solve quadratic equation: x = [OH ⁻] = 0.00116 M.

pOH = - log (0.00116 M) = 2.93.

pH = 14 - 2.93 = 11.07.