Question

A 0.250g sample of unknown acid requires 89.3 mL of 0.140 mol/L NaOH for complete neutralization. What is the molar mass of acid?

Answer 1

number of moles of NaOH = $0.140\textsf{M} ×\dfrac{89.3}{10^3}\textsf{ L}$ = $0.0125\textsf{ mol}$

Assuming X is monovalent

$HX+ NaOH \to NaX + H_2O$

This implies that one mole of the acid combines with one mole of the base,

$\therefore$ 0.0125 moles of the acid combines with 0.0125 moles of the base

0.0125 moles = 0.250g

1 mole = xg

x = $\dfrac{0.250}{0.0125}$ = $20\textsf{ g/mol}$