In water, HCN is a weak acid with pKa = 9.6.

a. Calculate the the Ka and the [H+] in a 0.15 M solution of HCN.

b. In a closed system, these equilibria are established:

HCN (g) s HCN (aq)

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

1) Calculate Kp for the equilibrium between HCN (g) and HCN (aq) at 298 K.

? Gf° kJ. mol-1

HCN (g) 124.7

HCN (aq) 119.7

2) If the total cyanide concentration in solution (i. e. [CN-] + [HCN]) is 0.10M, calculate the partial pressure of HCN (g) in this system at pH = 7.