A 23.16 ml volume of an H2A acid solution of unknown concentration with 2 drops of phenolphthalein required 14.24 ml of 0.135 M NaOH to reach the endpoint. What is the molar concentration of the acid solution?

Answer 1

H2A + 2NaOH ==> Na2A + 2H2O

mols NaOH = M x L = ?
Convert mols NaOH to mols H2A using the coefficients in the balanced equation. So mols H2A = 1/2 mols NaOH

Then M H2A = mols H2A/L H2A