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What is the pH of a 1.75 M solution of sodium cyanide, NaCN?
What is the pH of a 1.75 M solution of sodium cyanide, NaCN?
The Ka value of HCN is 6.2 x 10-10.
a. 10.04
b. 11.73
c. 9.20
d. 2.27
1 Answer
- hcbiochemLv 75 days ago
Equilibrium: CN- + H2O <--> HCN + OH-
Kb for CN- = 1X10^-14 / 6.2X10^-10 = 1.6X10^-5
Kb = [HCN][OH-]/[CN-] = 1.6X10^-5
Let [HCN] = [OH-] = x and [CN-] = 1.75-x. Assume that x will be small and can be ignored compared to 1.75. Then,
1.6X10^-5 = x^2 / 1.75
x = [OH-] = 5.31X10^-3
pOH = 2.27
pH = 14- pOH = 11.73
b. is the correct answer.
