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Science

Calculations and titrations

Percentage yield

The yield from a chemical reaction is the mass of product made.

A balanced symbol equation shows the number of atoms and molecules in the reactants and products. The reactants are on the left of the arrow and the products are on the right of the arrow.

A balanced equation can tell us the theoretical yield for a reaction, by using the relative formula masses of reactants and products involved.

For example the formula for the neutralisation of sulfuric acid with sodium hydroxide is:

sulfuric acid + sodium hydroxide → sodium sulfate + water

H2SO4 + 2NaOH → Na2SO4 + 2H2O

By using the relative formula masses it can be calculated that 6.9g of sulfuric acid theoretically produces 10g of sodium sulfate.

If this neutralisation reaction is carried out, the actual yield is found by measuring the mass of product - sodium sulfate - that has been made. The actual yield of sodium sulfate produced will be less than the theoretical yield calculated using the equation.

Theoretical vs actual yield

The difference between the theoretical yield and the actual yield for any reaction may have one or more of a number of causes:

  • Some of the reactants may remain unreacted when the reaction is complete.
  • Some of the product may be lost when liquids or solids are transferred from one container to another.
  • Some of the reactants may form other products.

If you have both the theoretical yield and actual yield, you can work out the percentage yield for the synthesis:

percentage yield = (actual yield ÷ theoretical yield) × 100

Question

In the neutralisation of sulfuric acid with sodium hydroxide, the theoretical yield from 6.9g of sulfuric acid is 10g. In a synthesis, the actual yield is 7.2g. What is the percentage yield for this synthesis?

toggle answer

Answer

percentage yield = (actual yield ÷ theoretical yield) × 100

percentage yield = (7.2 ÷ 10) x 100 = 72%

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