Yield (Edexcel GCSE Chemistry)

Revision Note

Stewart Hird

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Yield

Yield

  • Yield is the term used to describe the amount of product you get from a reaction

  • In practice, you never get 100% yield in a chemical process for several reasons

  • These include:

    • Some reactants may be left behind in the equipment

    • The reaction may be reversible and in these reactions a high yield is never possible as the products are continually turning back into the reactants

    • Some products may also be lost during separation and purification stages such as filtration or distillation

    • There may be side reactions occurring where a substance reacts with a gas in the air or an impurity in one of the reactants

    • Products can also be lost during transfer from one container to another

Actual & Theoretical Yield

  • 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 the reacting masses

  • The percentage yield compares the actual yield to the theoretical yield

  • For economic reasons, the objective of every chemical producing company is to have as high a percentage yield as possible to increase profits and reduce costs and waste

Percentage Yield

  • The percentage yield is a good way of measuring how successful a chemical process is

  • There are often several methods of creating a compound and each method is called a reaction pathway

  • Reaction pathways consist of a sequence of reactions which must occur to produce the required product

  • Companies often investigate and try out different reaction pathways and these are then compared and evaluated so that a manufacturing process can be chosen

  • The percentage yield of each pathway is a significant factor in this decision making process

  • The equation to calculate the percentage yield is:

Worked Example

Copper(II) sulfate may be prepared by the reaction of dilute sulfuric acid on copper(II) oxide. A student prepared 1.6 g of dry copper(II) sulfate crystals. Calculate the percentage yield if the theoretical yield is 2.0 g.

Answer:

  • Actual yield of copper(II) sulfate = 1.6 g

  • Percentage yield of copper(II) sulfate = (1.6 / 2.0) x 100

  • Percentage yield = 80%

Examiner Tips and Tricks

The actual yield can be determined by experiment only, while the theoretical yield can be calculated assuming there is 100% conversion of reactants to products.

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Stewart Hird

Author: Stewart Hird

Expertise: Chemistry Lead

Stewart has been an enthusiastic GCSE, IGCSE, A Level and IB teacher for more than 30 years in the UK as well as overseas, and has also been an examiner for IB and A Level. As a long-standing Head of Science, Stewart brings a wealth of experience to creating Topic Questions and revision materials for Save My Exams. Stewart specialises in Chemistry, but has also taught Physics and Environmental Systems and Societies.