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Percentage By Mass - GCSE Chemistry Definition

Reviewed by: Richard Boole

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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.

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Richard Boole

Reviewer: Richard Boole

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