How to Calculate Percent Yield

Chemistry involves experiments and calculations among other things. One of the basic equations that serve all chemistry students is how to calculate percentage yield. To find the percentage yield, you also need to calculate the actual and theoretical yield as well.

Difficulty: Moderately Challenging

Instructions

1. Make sure the calculation is balanced. If you have an unbalanced reaction presented to you, then you need to balance the equation first.

2. Find the limiting reagent and calculate the molecular mass or weight of the reactants and products. To find the limiting agent, divide the mass of the reactant by its molecular weight.

3. Determine molecular mass by writing out the formula, such as H2O for water, and look up the weight of each atom. For example, multiply the hydrogen atom weight by two and add it to the weight of oxygen.

4. Calculate the theoretical yield or how much will be synthesized under perfect conditions. Multiply the amount of moles of limiting reagent by the ratio, the synthesized product and molecular weight of the product.

5. Know the actual yield, or the amount of product truly synthesized in the original experiment. This involves no additional calculations. It is simply a factor taken from the experiment.

6. Use the calculation of percentage yield equals mass of actual yield divided by mass of theoretical yield multiplied by 100 percent.

Tips & Warnings

• A balanced chemical equation has the same amount of atoms on both sides of the equation.

Resources

• Tutorial on balancing equations including practice problems
• Detailed example of percentage yield and necessary calculations

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[chaverst]

on 1/19/2009 In Step 6:"Use the calculation of percentage yield equals mass of actual yield divided by mass of theoretical yield multiplied by 100 percent." This erroneous instruction is found in many chemistry books. Let's say the actual divided by the theoretical is equal to 0.65. When you multiply 0.65 by 100% you get 0.65. Multiplying anything by 100% is the same as multiplying it by 1. However, if you multiply 0.65 by 100 and express your answer as a percent, you have it correct. Students who use calculators (and which ones don't?) will punch in the "formula" times 100% and get it wrong every time.