For the following reaction, 15.2 grams of chlorine gas are allowed to react with 8.46 grams of water.

chlorine (g) + water (l) hydrochloric acid (aq) + chloric acid (HClO3) (aq)

What is the maximum amount of hydrochloric acid that can be formed?

To solve this problem, you must first balance the chemical equation and then identify the limiting reactant. The balanced reaction is 3Cl2 + 3H2O = 5HCl + HClO3. Next is finding the limiting reactant. To do this, you have to compare each reactant to the same product. 15.2 g of chlorine gas (Cl2), is equal to 0.214 mols of chlorine gas, and the mol to mol ratio of chlorine gas to hydrochloric acid is 3:5. So, for every 3 mols of Cl2 gas, there are 5 mols of HCl. 0.214mols Cl2 times (5/3) gives you 0.357 mols of HCl. Next you have to go through the same process except with water. 8.46g water divided by 18.016g water per mol = 0.470 mols H2O. The mol to mol ration is still 3:5, so 0.470 times (5/3), which gives you 0.783mols HCl. A chemical reaction is limited based on the amount of reactants present, and so the reaction is limited by whichever reactant runs out first. In this case, the limiting reactant is chlorine gas because it produced a smaller amount of HCl, and therefore the "limit" of the reaction. This means that the maximum amount of HCl that can form is 0.357 mols, or 13.016 grams of HCl if the answer is supposed to be given in grams.