Relative molecular mass (Mr)
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
Relative atomic mass (Ar)
- 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
Relative formula mass
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
You got it now!