Question

You need to determine the concentration of a sulfuric acid solution by titration with a standard sodium hydroxide solution. You have a 0.1920 M standard solution. You take a 25.00 mL sample of the original acid solution and dilute it to 250.0 mL. You then take a 10.00 mL sample of the dilute acid solution and titrate it with the standard solution. You need 19.18 mL of the standard solution to reach the endpoint. What is the concentration of the original acid solution?

Answer 1

M1=concentration of acid solution

Moles of acid in 25ml = M1*25/1000

This is diluted to 250 ml. Then Molarity (from M1V1= M2V2)

M2= M1*25/1000= M2*250/1000

M2= M1/10

10ml of the solution having M2 Molarity is taken and titrated with 0.192M NaOH solution that consumed 19.8 ml NaOH and the reaction is

2NaOH+ H2SO4-->Na2SO4 + H2O

Moles of NaOH= 0.192*19.8/1000=0.003802

Moles of acid consumed= (M1/10)*10/1000 = M1/1000

2 moles of NaOH requires 1 mole of H2SO4

0.003802 moles requires 0.003802/2=0.001901

This is equal to M1/1000

M1/1000= 0.001901

M1= 1.9M