1.2.2 molar mass
Mole
definition
the amount of any substance, which contains the same number of particles ⚠(atoms, ions, molecules, formulae or electrons) as there are carbon atoms in exactly 12 g of the carbon -12 isotope.
⭐ the Avogadro constant 
The number of atoms per mole of carbon-12 isotopes: 6.02e23 mol^-1
1 mole of chlorine atoms =6.02e23 atoms
Molar mass
1 mole of chlorine molecules=6.02e23 molecules
=1.204e24atoms
the mass per mole of a substance,[g/mol]
Moles to Mass
FORMULAR: Mass= Moles x Molar Mass
m(g)=n(mol) x Mr(g/mol)
EXAMPLE
Masses to Moles
FORMULAR: Moles= Mass/Molar Mass
n(mol)=m(g)/Mr(g/mol)
EXAMPLE
Moles to Molar Mass
FORMULAR: Molar Mass= mass/ moles
Mr(g/mol)=m(g)/n(mol)
Significant figures
Scientific notation
only pays attention to the mantissa and ignore the 10^n part
multiplication and division
Addition and subtraction
multiplication and division
EXAMPLE
STEP 1: Find the number has the least significant numbers
STEP 2: The result must have the same number of significant figures as that number.
The use of scientific notation: when the significant figure is hard to achieve since they are a whole number/ large number
eg:7.100 x 10^23 has 4sf (zeros counts since they are at the right hand of the constant )
Zeros:
If it is at the left of a non-zero number: does not count.
If it is at the right of a non-zero number, only counts when there is a decimal place.
When it has decimal places: 0.498=4.98x10^-1
If it is measured by top ban balance, such as 560g, the zero counts. So it has 3 significant figures.
Apply molar mass calculation in chemical equations