A buffer solution - HNO2/NH3?

Question

How can weak acid nitrous acid HNO2 form a buffer solution with equal concentrations and volumes with weak base NH3?

I thought that buffer solutions only occured between weak acids and strong bases or vice versa. The example above as two weak soltuions.

Answer 1

A buffer solution usually consists of a mixture of a weak acid and its conjugate base.

But in this case there are simply an acid and a base that don't react much with each other that each react with H+ or OH-

The equilibrium for this reaction lies far to the left

NH3 + HNO2 <==> NH4+ + NO2-

The addition of H+ will cause this reaction:

NH3 + H+ <==> NH4+

The addition of OH- will cause this reaction

HNO2 + OH- <==> HOH + NO2-

So this mixture could be considered a crude buffer solution.