gases heading

Chemistry only

Percentage yield

good idea 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 it substance C. Your method is to use the reactants A and B to make your desired product C.

A + B → C
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 100% of your reactants should turn into the desired product. The theoretical yield of a reaction is the mass of the product you expect to make based on your calculations and 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 yield would be the same, and be 100%. Unfortunately in the real world actual yields are rarely if ever 100%.

chemical reactions rarely have 100% yields There are many reason why yields are never 100%, these include:


% yield

To calculate the % yield of a reaction use the formula below:

formula for % yield

Examples

In an experiment Joe made 7g of substance A. He calculated that the maximum mass of product should be 10g. What is the % yield of the reaction?
Simply use the equation given above to calculate the % yield.

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

Example 2:
2.5g of new drug is made but the scientists were expecting a maximum yield of 15g. What is the % yield for this reaction? So simply substitute these numbers into the formula to give:
% yield = (2.5g/15g) x 100% = 17% yield.

Practice questions

Check your understanding - complete the following practice questions

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