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Percentage yield calculations

You might spend a lot of time working out a method to make a product that you hope to sell for vast profit, let's call this money making substance; substance C. Your method is to use the reactants A and B to make your desired product C.

A + BC
Looking at this equation it would appear at first glance to be a good method to make substance C, there are no other products so the atom economy is 100% since all of the reactants A and B form one single product.


Theoretical yield and actual yields

Info graphic to explain the difference between actual and theoretical yields in a chemical reaction. Now you probably already know that you can use mole type calculations to work out the theoretical yield of a reaction, that is the mass of the product you expect to make based on how much of the reactants, A and B you intend to measure out and use. While the actually yield is the mass of the product that you actually manage to make, and that you can bottle up and sell. In an ideal world the theoretical yield, the calculated yield and actual yields would be the same.

You might expect that you would get 100% of the product you expect, unfortunately in the real world actual yields are very different from the expected calculated theoretical yield and are very rarely if ever 100%.

Why you never get what you expect!

Yields obtained from carrying out a practical activity are never 100%, that is you never manage to make all the product you expect, no matter how carefully you carry out the experiment; these include:


Percentage yield

The percentage yield of a chemical reaction is the ratio of the actual yield to the theoretical or calculated yield multiplied by 100. It shows how efficient a reaction is at producing the desired product. To calculate the percentage yield of a reaction use the formula below: formula for % yield

Self-check

Review your understanding of percentage yields by completing the activity below. Simply click or drag the statements into the true or false bins and click the check answer button when you are done.

Statements

Place into True / False


Example calculations

In an experiment Joe made 7g of substance A. He calculated that the maximum theoretical mass of product should have been able to make was 10g. What is the percentage yield of this reaction?
Simply use the equation given above to calculate the percentage yield,.

Simply substitute these numbers into the equation to get the percentage yield.
Percentage yield = (7g/10g) x 100% = 70% yield.

Example 2:


2.5g of new drug is made but the scientists were expecting a maximum theoretical yield of 15g. What is the percentage yield for this reaction? So simply substitute these numbers into the formula to give:
Percentage yield = (2.5g/15g) x 100% = 17% yield.


Self-check- percentage yield calculations

Calculate the percentage yield for the reactions in the questions below; press the check answer button when you are done. You will need to use mole calculations to calculate the masses of products produced in these reactions before you can work out percentage yields. If you prefer to work on these questions off-line then click here to download all the questions and answers.


Percentage Yield Practice

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Equation

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Data

Given Ar
Mr (each species)

Practice questions and % yield calculator

Percentage Yield Calculator

Enter the theoretical yield and actual yield to find % yield.

Formula: % yield = (actual ÷ theoretical) × 100

Review your understanding of percentage yields by completing the questions on the worksheets below; simply click the links to open the worksheets or alternatively use the % yield calculator opposite, simply enter the theoretical and actual yields to obtain the percentage yield but calculate the percentage yield yourself before pressing the calculate % yield button.


Check your understanding - questions on percentage yields

Check your understanding - additional questions on percentage yields

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