Percentage Yield

Specification Point 5.11C:
  • Calculate the percentage yield of a reaction from the actual yield and the theoretical yield.
  • Yield is the term used to describe the amount of product you get from a reaction.
  • The actual yield is the recorded amount of product obtained.
  • The theoretical yield is the amount of product that would be obtained under perfect practical and chemical conditions.
  • It is calculated from the balanced equation and reacting masses.
  • The percentage yield compares the actual yield to the theoretical yield.

Equation:

Percentage Yield     =    (actual yield  ÷ theoretical yield) x 100

Example:

In an experiment to displace copper from copper sulfate, 6.5g of zinc was added to an excess of copper (II) sulfate solution. The copper was filtered off, washed and dried. The mass of copper obtained was 4.8g. Calculate the percentage yield of copper.

Equation of Reaction:    

Zn (s)    +    CuSO4 (aq)     →     ZnSO4 (aq)    + Cu (s)

Step 1  Calculate the Moles of Zinc Reacted

Moles of Zinc = 6.5 ÷ 65 = 0.10 moles

Step 2  Calculate the Maximum Amount of Copper that could be formed from the

Molar ratio

Maximum Moles of Copper = 0.10 moles (Molar ratio is 1:1)

Step 3  Calculate the Maximum Mass of Copper that could be Formed

Maximum Mass of Copper = ( 0.10 x 63.5 ) = 6.35 g

Step 4  Calculate the Percentage Yield of Copper

Percentage Yield = ( 4.8 ÷ 6.35 ) x 100 = 75.6%

Percentage Yield of Copper = 75.6%

Actual & Theoretical Yield

Specification Point 5.12C:
  • Describe that the actual yield of a reaction is usually less than the theoretical yield and that the causes of this include:
    a) incomplete reactions
    b) practical losses during the experiment
    c) competing, unwanted reactions (side reactions)
  • In practice, you never get 100% yield in a chemical process for several reasons. 
  • These include:
    • The reaction not going to completion as not all of the reactants are converted to products.
    • Some product may be left behind in the equipment or lost during transfer or separation stages.
    • Side reactions may occur where some of the products react to form unwanted substances caused by changes in reaction conditions or impurities.
  • Low yield reactions are costly as a lot of the reactants are wasted so companies try to use as many high yield processes as possible to maximise profits.

Edexcel GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.