In I/GCSE Chemistry, we will learn about atomic masses and moles.

Weighted mean mass of a molecule compared with 1/12 of the mass of an atom of carbon-12.

Mr of Cl₂ = 35.5 x 2 = 71.0

Mr of H₂O =(1.0 x 2) + 16.0 = 18.0

• Weighted mean mass of an element compared with 1/12 of the mass of an atom of carbon-12.
• In I/GCSE Chemistry, it can be determined by using an instrument called a MASS SPECTROMETER
• Depends on:
  • Percentage abundance of the isotope
  • The relative mass of the isotope

Weighted mean mass of a formula unit compared with 1/12 of the mass of an atom of ccarbon-12.

CaBr₂ = 40.1 + (79.9 x 2) = 199.9

Na₃PO₄ = (23.0 x 3) + 31.0 + (16.0 x 4) = 164.0

• In I/GCSE Chemistry, amount of any substance containing as many particles as there are carbon atoms in exactly 12g of carbon-12 isotope.
• SOLIDS- A measure of the number of particles contained within a substance
• SOLUTION- CONCENTRATION- The amount of substance measured in moles that would be dissolved in one decimetre cubed of solution

• Concentration= moles/volume
• Mass (g)= moles x Mr (formula mass)
• Concentration in gdm ⁻³= concentration in moldm⁻³ x Mr of solute

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