Topic 2: Amount of a substance
Relative atomic mass and relative molecular mass
Relative atomic mass - The mass of an atom compared to the mass of 1/12th
of a Carbon-12 atom
Relative molecular mass - The mass of a molecule compared to the mass of 1/12th
of a Carbon-12 atom
Relative formula mass - used for ionic compounds
The mole and the Avagadro constant
Avagadro constant - 6.022 x 10
Number of particles = moles x avagadro’s constant
Mr x moles = mass (Mr moles carries mass)
The concentration of a substance in solution, is measured in mol dm–3.
Moles = concentration (mol dm-3) x volume (dm3)
1 dm3 = 1000 cm3
The ideal gas equation
Gas constant = 8.31
Empirical and Molecular Formula
Empirical formula is the simplest whole number ratio of atoms of each element in a
compound.
Molecular formula is the actual number of atoms of each element in a compound
The molecular formula is always a whole number multiple of the empirical formula.
Relative atomic mass and relative molecular mass
Relative atomic mass - The mass of an atom compared to the mass of 1/12th
of a Carbon-12 atom
Relative molecular mass - The mass of a molecule compared to the mass of 1/12th
of a Carbon-12 atom
Relative formula mass - used for ionic compounds
The mole and the Avagadro constant
Avagadro constant - 6.022 x 10
Number of particles = moles x avagadro’s constant
Mr x moles = mass (Mr moles carries mass)
The concentration of a substance in solution, is measured in mol dm–3.
Moles = concentration (mol dm-3) x volume (dm3)
1 dm3 = 1000 cm3
The ideal gas equation
Gas constant = 8.31
Empirical and Molecular Formula
Empirical formula is the simplest whole number ratio of atoms of each element in a
compound.
Molecular formula is the actual number of atoms of each element in a compound
The molecular formula is always a whole number multiple of the empirical formula.
