chemistry - molar mass and the mole

Relative formula mass

• the sum of the relative atomic masses of all atoms as given in the chemical formula of species

• Applies to molecular & non-molecular substance such as ionic solids

Relative molecular mass

• the mass of a molecule relative to carbon-12 → which is assigned to a mass of exactly 12

  • Only applies to molecular covalent subastance

Chemical quantities

• we measure substances → use mass & volume

• Molecules react in specific ration during a chemical reaction

→ balanced equations tell us about ratio that each atom will react

The mole reasoning

• working with individual atoms and moles = impractical because of small size/ mass

• Instead - chemist work with a number of them that’s large so confident and can be weighed out in lab

The mole

• mole is a quantity used by chemists when working with any chemical species

→ definition - the amount of substance that contains the same number of particles as there are atoms in exactly 12g of carbon-12 atoms

• means 1 mole of carbon-12 atoms = mass of 12g

Avogardos constant

• the number of atoms in 1 mole of carbon-12 has been determined to be 6.02 × 10²³

Relationship btwn number of particles in 1 mole and avagardos constant

N(no.of particles in sample)= n(no.of mole) X Na(A number)

Molar mass

• the mass of one mole of a substance

• For an element - it is its relative atomic mass measured in grams (g/mol)

• For a compound - it is its relative formula or molecular mass expressed in grams (g/mol)

Molar mass - relationship

M (mass of substance in grams) = n(no.of mole, in mol) X M(molar mass in gmol^-1)