Question

Be sure to answer all parts. At what concentration does hydrocyanic acid (Ka = 4.9 × 10−10) exhibit 0.05 percent ionization? Assume the temperature to be 25°C. × 10 M At what concentration does hydrocyanic acid exhibit 0.10 percent ionization? Assume the temperature to be 25°C. × 10 M At what concentration does hydrocyanic acid exhibit 0.15 percent ionization? Assume the temperature to be 25°C. × 10 M

Answer 1

part 1)

Ka = 4.9 x 10^-10

% ionization = 0.05 %

HCN (aq)   -------------> H+ (aq) + CN- (aq)

x                                      0               0

x- 0.05x/100                      0.05x/100       0.05x/100

Ka = (0.05x/100)^2 / (x -0.05x/100 )

4.9 x 10^-10 = ((0.05)^2 x / 100) x 1 / 99.95

x = 2.0 x 10^-3

concentration of HCN = 2.0 x 10^-3 M

part 2)

% ionization = 0.10 %

Ka = (0.10 x /100)^2 / (x - 0.10x / 100)

4.9 x 10^-10 = (0.10)^2 x / 100 x (1 / 99.90)

x = 4.9 x 10^-4

concentration of HCN = 4.9 x 10^-4 M

part 3)

% ionization = 0.15 %

concentration = 2.2 x 10^-4 M