Calculate the percent ionization of ha in a 0.10 m solution.

Question:

Calculate the percent ionization of ha in a 0.10 m solution.

Answer & Explanation:

Question:

A certain weak acid, HA, has a Ka value of 1.1 * 10-7.
Part A
Calculate the percent ionization of HA in a 0.10 M solution.
Part B
Calculate the percent ionization of HA in a 0.010 M solution.
Calculating the Degree of Dissociation of Weak Acids
Consider a weak monoprotic acid of the form HA . Let its concentration be c and dissociation constant be KaConsider a weak monoprotic acid of the form HA . Let its concentration be c and dissociation constant be Ka
The general chemical equation depicting the ionization of HA is :
HA ⇋ H + A−
c(1−α) cα cα
α is the degree of dissociation of the acidα is the degree of dissociation of the acid
∴Ka=[H+][OH−]/[HA]
⇒Ka=(cα)(cα)/c(1−α)
⇒Ka=cα2/1−α (1)
⇒cα2+αKa−Ka=0

Hence, the degree of dissociation can be evaluated by solving the above quadratic equation.

When the dissociation constant Ka has a very small value, we can use approximations in equation (1) to find the degree of dissociation.
1−α≈1
⇒Ka=cα2
⇒α=√Kac

Answer and Explanation:
(a)Ka=1.1×10−7
c=0.1 M
∴α=√Ka/c
⇒α=√1.1×10−7/0.1
⇒α=1.048×10−3=0.1048%

(b)Ka=1.1×10−7
c=0.01 M
∴α=√Ka/c
⇒α=√1.1×10−7/0.01
⇒α=3.316×10−3=0.3136%