Question

A chemistry graduate student is given 250.mL of a 1.60M chlorous acid HClO2 solution. Chlorous acid is a weak acid with =Ka×1.1 x 10^2. What mass of NaClO2 should the student dissolve in the HClO2 solution to turn it into a buffer with pH =1.45?

Answer 1

28.04g of NaClO2 must be dissolved

Step-by-step explanation:

When NaClO2 and HClO2 are mixed in a solution, a buffer is produced. The pH of this buffer is obtained using H-H equation:

pH = pKa + log [NaClO2] / [HClO2]

Where pKa is -log Ka = 1.9586

And [NaClO2] and [HClO2] could be taken as moles of each compound.

Moles of HClO2 are:

250mL = 0.250L * (1.60mol / L) = 0.40 moles HClO2.

Replacing:

pH = pKa + log [NaClO2] / [HClO2]

1.45 = 1.9586 + log [NaClO2] / [0.40mol]

0.31mol = [NaClO2]

To convert these moles to mass we need to use molar mass of NaClO2: 90.44g/mol:

0.31mol * (90.44g / mol) =

28.04g of NaClO2 must be dissolved