In a titration, 50 cm3 of sodium hydroxide with a concentration of 0.3 mol/dm3 was neutralised by 60 cm3 of hydrochloric acid. Calculate the concentration of the hydrochloric acid in mol/dm3.

HCl + NaOH = NaCl + H2O. Moles = volume (dm3) x concentration (mol/dm3). Moles of NaOH: volume x concentration = (50/1000) x 0.3 = 0.015 moles. 1 to 1 ratio of HCl to NaOH, so there were 0.015 moles of HCl. Concentration of HCl: moles/volume = 0.015/(60/1000) = 0.25 mol/dm3.