Cambridge O Level Chemistry · Syllabus 5070 · Stoichiometry
Percentage composition by mass
What is Percentage composition by mass?
Percentage composition by mass is the mass contributed by a specified element within a compound's formula divided by the compound's relative molecular or formula mass, multiplied by 100 per cent.
This definition is part of the Stoichiometry chapter in Cambridge O Level Chemistry.
Questions students ask about Percentage composition by mass
How do you calculate percentage yield, percentage purity and percentage composition?
Write the fraction in words before you write it in numbers, so it cannot go in upside down. Percentage yield is the mass of product actually obtained divided by the theoretical maximum predicted from the balanced equation, times 100. Percentage purity is the mass of the pure substance divided by the total mass of the impure sample, times 100. Percentage composition by mass is the mass of one element in the formula divided by the relative formula mass, times 100. Then check the unit and the scale of the answer.