Hurrr a buffer is made using hco2na. which other substance should the buffer contain?

To answer this problem, let us first define what a buffer solution is.

A buffer solution by definition is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or a weak base and its conjugate acid.

In this case, we have are going to have a mixture of a weak acid and its conjugate base. Sodium Formate or HCOONa is the conjugate base of that weak acid. Sodium formate is properly written as:

HCOO-Na+

We can find the weak acid by replacing Na+ with H+. Therefore, the other substance should be:

HCOO-H+

or

HCOOH

Formic Acid = HCOOH