An unknown acid (0.2922 g) was titrated with 0.100 M. sodium hydroxide.

Question

An unknown acid (0.2922 g) was titrated with 0.100 M. sodium hydroxide. The equivalence

point required 20.00 mL. The pH at the point where 10.00 mL had been added was 4.40.

Identify the unknown acid, using data from Table 1.

the table has pKa and the compund next to it

so if i get the pKa that will help

Answer 1

the pH at 1/2 reactions equals the pKa, so the pKa is 4.40

let's get total moles:

0.020 litres @ 0.1 mol/litre = 0.002 moles of NaOH

since they only talk about 1 equiv point:

0.002 moles of NaOH = 0.002 moles of acid

let's get molar mass of the acid:

0.2922 grams/ 0.002 moles = 146.1 grams / mol3

your answers are : PKa = 4.40,  Molar mass = 146.1 g/mol