Find the concentration of calcium carbonate given that 25cm^3 of CaCO3 is neutralised by an average of 14cm^3 of 0.1 molar HCl .

Initially it helps to read over the question a couple of times underlining/ highlighting all important information ie. volumes and concentrations. Next it always helps to have a chemical equation to work with so if you're not already given one in the question write one out, ensuring it is balanced. The next step is to work out the number of moles of HCl- (140.1)/1000 = 1.410^-3 mol - and use this to work out the number of moles of CaCO₃ (using mole ratios - in this case 1:2) - 1.410^-3/2 = 710^-4 mol. From this we can work out the concentration of CaCO₃: [CaCO₃] = (7*10^-4 * 1000)/ 25 = 0.028moldm^-3.