3.3.1 Percentage Yield

In this lesson, we will explore the concept of percentage yield and learn how to calculate it.

Factors Affecting Yield

There are several reasons why the actual yield of a product may be less than the calculated or expected yield:

• Reversible Reaction: Some reactions are reversible, meaning they can proceed in both forward and reverse directions. As a result, the reaction may not go to completion, leading to a lower yield.
• Product Loss: During the separation or purification process, some of the product may be lost or left behind in the reaction mixture or apparatus.
• Side Reactions: Sometimes, the reactants may undergo unexpected reactions or form by-products, reducing the overall yield of the desired product.

Yield and Percentage Yield

The yield refers to the amount of product obtained from a reaction. It can be measured in grams, moles, or any other appropriate unit. The percentage yield is calculated by comparing the actual yield to the maximum theoretical yield and expressing it as a percentage using the following formula:

Percentage Yield = (Mass of Product Actually Made / Maximum Theoretical Mass of Product) x 100

Calculating Percentage Yield

To calculate the percentage yield, you need to know the actual yield of the product and the maximum theoretical yield. The actual yield is determined through experimental measurements, while the maximum theoretical yield is calculated based on stoichiometry and the balanced equation for the reaction.

Example Calculation

Let's consider an example:

If the maximum theoretical yield of a product is 50 grams and the actual yield obtained is 40 grams, we can calculate the percentage yield as follows:

• Percentage Yield = (40 g / 50 g) x 100
• Percentage Yield = 80%

Interpreting Percentage Yield

A high percentage yield indicates that the reaction is efficient and that a significant amount of the desired product has been obtained. Conversely, a low percentage yield suggests that there were inefficiencies or losses during the reaction.

Conclusion

Percentage yield allows us to assess the efficiency of a reaction and determine the extent to which the calculated yield has been achieved. By calculating the percentage yield, we can identify factors that may have limited the yield and work towards improving the reaction conditions or purification methods.