DRAFT GCSE Chemistry- Quantitative Calculations DRAFT

actually the hardest part of chemistry (y10 content)

Percentage equation

(Mass of element ÷ mass of compound) x 100

Relative Atomic Mass (A_r)

The average mass of an atom of an element, compared to 1/12^th of the mass of an atom of carbon-12

Relative Formula Mass (M_r)

The sum of the relative masses of atoms in a compound

Find the percentage mass of Sodium (Na) in Sodium bromide (NaBr)

A_r of Na = 23

A_r of Br = 80

• (23/(23+80)) x 100

  • 22%

Avogadro’s Number

6.02 × 10²³

Equation to figure out mole

Mole = Mass x M_r

Units for Moles

mol

Units for mass

g

Units for formula mass

g mol^-1

What is one mole of a substance?

The amount that contains an Avogadro’s number of particle

Equation to figure out numbers of molecules

No. of molecules = moles x (6.02 × 10²³)

Equation for number of atoms

No. of atoms = no. of molecules x 2