Buffer Solution Chemistry Math Question 7

Question

How many grams of sodium nitrite must be added to 300.0 mL of 0.3 M nitrous acid in order to prepare a buffer solution at pH 3.5? The pK_a of nitrous acid is 3.337.

Answer 1

This is analogous to your previous question (#6) where you will use the HH equation, solve for log (salt/acid) and then find moles of salt, and finally convert to grams of salt.

pH = pKa + log [salt]/[acid]

pH = 3.5

pKa = 3.337

[acid] = 0.3 M

3.5 = 3.337 + log (x/0.3)

Solve for x which will give you M (molarity) of sodium nitrate needed. Use the volume of 300 ml (0.300 L) to convert that to moles needed and finally, multiply that by the molar mass of sodium nitrate to obtain grams needed.

Again, refer to your previous question #6 which is solved in an identical manner as this problem.