GlossariesGCSE GlossariesGCSE Chemistry GlossaryPercentage By Mass

Percentage By Mass - GCSE Chemistry Definition

Reviewed by: Richard Boole

Last updated

Percentage by mass shows how much of a specific substance is present in a mixture or compound, compared to the total mass. It is calculated using the formula:

fraction numerator mass space of space element over denominator total space mass space of space chemical end fraction × 100

This gives the percentage of the substance in the mixture.

For example:

  • Sodium (Na) has an atomic mass of 23

  • Chlorine (Cl) has an atomic mass of 35.5

  • This means that the relative formula mass of sodium chloride (NaCl) is 23 + 35.5 = 58.5

  • So, the percentage of sodium in sodium chloride is:

fraction numerator 23 over denominator 58.5 end fraction x 100 = 39.3% Na

This method helps us understand the composition of compounds clearly and is often used in chemical analysis.

Examiner-written GCSE Chemistry revision resources that improve your grades 2x

  • Written by expert teachers and examiners
  • Aligned to exam specifications
  • Everything you need to know, and nothing you don’t
GCSE Chemistry revision resources

Share this article

Richard Boole

Reviewer: Richard Boole

Expertise: Chemistry Content Creator

Richard has taught Chemistry for over 15 years as well as working as a science tutor, examiner, content creator and author. He wasn’t the greatest at exams and only discovered how to revise in his final year at university. That knowledge made him want to help students learn how to revise, challenge them to think about what they actually know and hopefully succeed; so here he is, happily, at SME.

The examiner written revision resources that improve your grades 2x.

Join now