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Percentage Composition

What is the Percentage Composition of a Compound or Mixture?

This post will introduce the concept of percentage composition for Prelim Chemistry.

Percentage composition looks at the fraction of a certain element in a compound, or the fraction of a certain compound in a mixture (e.g. the fraction of sand in a mixture of sand, iron filings, and salt). The fraction is found through the division of the mass of what you wish to find against the total mass of the compound or mixture. It is a common technique used in the gravimetric analysis (quantitative analysis of a mixture/compound based on mass).

Topic: Properties of Matter

  • Explore homogeneous mixtures and heterogeneous mixtures through practical investigations:
    • Using separation techniques based on physical properties
    • Calculating percentage composition by weight of component elements and/or compounds


How to Find Percentage Composition

Here is a video to explain how to find percentage composition.


(Note, if you wish to find the percentage composition of a certain compound in a mixture, you apply the same technique except 100% will be the total mass of the mixture.

e.g. a mixture of 250g of salt, sand, and iron filings has 50g of salt, 175g of sand, and 25g of iron filings. The percentage composition of sand in the mixture will be the mass of sand  (175g) over the total mass (250g) = ((175g/250g)*100)% = 70%  So the mixture is made up of 70% sand).


Further Examples

Here is another video with some more examples.