Question

Calculate the pH of a solution that is 0.253 M in nitrous acid (HNO2) and 0.111 M in potassium nitrite (KNO2). The acid dissociation constant of nitrous acid is 4.50 ⋅ 10-4. One of these answers is the correct one.

	2.992
	11.01
	14.36
	3.708
	4.898

Answer 1

Answer –

We are given, [HNO₂] = 0.253 M, [NO₂^-] = 0.111 M

K_a(HNO₂) = 4.5*10^-4

We need to use Henderson Hasselbalch equation-

pH = pKa + log [NO₂^-] / [HNO₂]

Now first we need to calculate the pKa from the given Ka

we know formula,    

pKa = - log Ka

        = - log 4.50*10^-4

         = 3.35

pH = 3.35 + log 0.111 M / 0.253

     = 2.99

the pH of a solution that is 0.253 M in nitrous acid (HNO2) and 0.111 M in potassium nitrite (KNO2) is 2.99, so correct option is 2.992