The hydrolysis of an ester is followed by acid-base titration. We take a sample of 30.0 cm3 from the reaction mixture which was originally a 0.02 M NaOH solution. We put the sample 50.0 cm3 0.02 M HCl solution and for the back titration of the acid we needed 25.3 cm3 0.02 M NaOH solution. Calculate the concentration of the ester which reacted.