A chemistry graduate student is given 500.mL of a 0.40M chlorous acid HClO2 solution. Chlorous acid is a weak acid with =Ka×1.110−2. What mass of NaClO2 should the student dissolve in the HClO2 solution to turn it into a buffer with pH =2.11?

Answer : The  mass of should be, 23.5 grams.

Explanation : Given,

Concentration of = 0.40 M

Volume of solution = 500 mL = 0.5 L

pH = 2.11

First we have to calculate the value of .

The expression used for the calculation of is,

Now put the value of in this expression, we get:

Now we have to calculate the concentration of

Using Henderson Hesselbach equation :

Now put all the given values in this expression, we get:

Now we have to calculate the moles of

Now we have to calculate the mass of

Molar mass of = 90.44 g/mol

Therefore, the mass of should be, 23.5 grams.