Want have equal amount the acid and its conjugate base

To prepare a buffer solution with a pH of 3.200 using nitrous acid (HNO2) and sodium hydroxide (NaOH), we need to determine the appropriate amounts of each solution to mix.

First, let's write the balanced chemical equation for the reaction between nitrous acid (HNO2) and sodium hydroxide (NaOH):

To find the required volume of 0.273 M sodium hydroxide, we'll use the Henderson-Hasselbalch equation:

pH = pKa + log([A-]/[HA])

log([NO2-]/[HNO2]) = 3.200 - 3.34

log([NO2-]/[HNO2]) = -0.14

Volume of sodium hydroxide = Volume of nitrous acid × ([NO2-]/[HNO2])

Volume of sodium hydroxide = 125 mL × 0.449