Answer to Question #67701 in General Chemistry for Aly

Question

The value of Ka for hydrocyanic acid is 4.00×10-10.
What is the value of Kb, for its conjugate base, CN-?

Answer 1

The Ka for an acid and Kb for a conjugate base are related to each other according to the equation
K_a*K_b=10^(-14).
So, the value of Kb for CN is
K_b (CN^- )=(10^(-14))/(K_a (HCN) )=(10^(-14))/(4*10^(-10) )=2.5*10^(-5).
Answer: Kb (CN ) = 2.5*10-5.