Stoichiometry Module: Chemical Analysis

Chemical Analysis

Once you are comfortable with stoichiometry calculations, you can use chemical reactions to analyze materials. Most materials you encounter on a daily basis are not pure substances; they are mixtures of two more more substances.

For example, the active ingredient in many antacids is calcium carbonate (CaCO₃). However, if you look at the ingredient listing on a bottle of antacid, you will see many other ingredients. How could you determine how much of the antacid tablet is actually calcium carbonate?

One possibility is to add something to the tablet that will react only with the calcium carbonate. If the amount of one of the products can be measured, the amount of calcium carbonate can be found using stoichiometry. For example, calcium carbonate reacts with hydrochloric acid:

Move mouse over formulas to see names.

From this balanced chemical equation, you can see that for every mole of calcium carbonate that is present initially, one mole of carbon dioxide will be produced.

Suppose a 1.00 g antacid tablet is treated with an excess of hydrochloric acid and 0.32 g carbon dioxide is produced. From this information, the amount of calcium carbonate in the tablet can be determined by following simple steps:

Step 1:Convert grams of product to moles of product.

Step 2:Calculate how many moles of the desired reactant would produce that amount of product using the balanced chemical equation.

Step 3:Convert moles of reactant to grams of reactant.

Step 4:Use this information to do any final calculations necessary.