When you mix chemicals, you often find a difference between how much product is actually made and how much theoretically should have been made. To determine how close you are to your goal, use a percent yield calculation. Yield indicates the products that are made in a chemical reaction.

Suppose you place a 25-gram piece of copper metal into a liquid solution of silver nitrate, because you have been told you can make silver this way. When you calculate the theoretical yield of silver, which is the maximum amount that can possibly be produced, you find that you should make 85 grams of silver. Yet, when you place the silver product from your experiment on the laboratory scale, you may see that it weighs only 82 grams. This is your actual yield.

To determine percent yield, divide the actual yield by the theoretical yield and multiply by 100. For this example, use the equation: 82 grams of silver / 85 grams of silver x 100 = 96 percent. This percentage tells you the efficiency of the chemical reaction, or how good the reaction is at actually producing the desired product. High percentages such as this one indicate better yields, and low percentages indicate poor yields.