Question

Nitric acid (HNO3) is a strong acid that is completely ionized in aqueous solutions of concentrations ranging from 1% to 10% (1.50 M ). However, in more concentrated solutions, part of the nitric acid is present as un-ionized molecules of HNO3. For example, in a 50% solution (7.50 M ) at 25°C, only 33% of the molecules of HNO3 dissociate into H+ and NO3–. What is the value of Ka for HNO3?

Answer 1

The value of the
`K_a` of the nitric acid is 1.2.

Step-by-step explanation:

The initial concentration of nitric acid = c = 7.50 M

`1 mM =m 10^(-3) M`

The dissociation constant of nitric acid =
`K_a`

Degree of dissociation of nitric acid =
`\alpha =33\%=0.33`

`HNO_3\rightleftharpoons NO_3^(-)+H^+`

initially

c 0 0

At equilibrium

(c-cα) cα cα

The expression of dissociation constant :

`K_a=([NO_3^(-)][H^+])/([HNO_3])`

`K_a=(c* \alpha * c* \alpha )/(c-c\alpha)`

`K_a=(c* (\alpha )^2)/((1-\alpha ))`

`K_a=(7.50 M* (0.33)^2)/((1-0.33))=1.2`

The value of the
`K_a` of the nitric acid is 1.2.