In this example, we'll look at the titration of a weak acid with a strong base. Our strong base is sodium hydroxide, and we use 17.9 milliliters of 0.151 molar sodium hydroxide to titrate 25 milliliters of a phosphoric acid solution. We want to calculate the concentration of this phosphoric acid solution. Our first step is to write a balanced chemical equation for the acid-base titration reaction. It will be: 3 sodium hydroxide + 1 phosphoric acid 3 water + sodium phosphate Next, we can write the information below the species in the balanced chemical equation that we know from the problem. To solve this problem, we'll want to use dimensional analysis. We're going to start with the 17.9 milliliters of sodium hydroxide solution. We want to end up with moles of phosphoric acid, so our first step is to convert from milliliters of solution into liters of solution. Then, we can use the molarity of sodium hydroxide to convert from liters of sodium hydroxide solution into moles of sodium hydroxide. The next step is to use stoichiometry to convert from moles of sodium hydroxide into moles of phosphoric acid. If you put this into your calculator, you should get 9.01 times 10 to the negative fourth moles of phosphoric acid. Next, we can use the moles of phosphoric acid and the milliliters of phosphoric acid solution to determine the molarity. The molarity is the moles of solute divided by liters of solution. So, we use our moles of solute that we've just calculated and convert 25 milliliters of phosphoric acid solution into liters (0.0250 liters). If you put this in your calculator, you should get 0.0360 molar phosphoric acid.