2.3 AMOUNT OF SUBSTANCE

Carbon-12 is the standard isotope used to base all atomic masses on

Avogadro’s constant is the number of particles per mole of substance. 6.02x10^26

Amount of substance is a quantity used to count the number of particles in a substance, measured in moles

Molar mass is the mass of 1 mol of substance measured in g/mol

Amount of substance (mol) = mass (g) / molar mass (g)

The molecular formula is the number of atoms of each element in a molecule - O2, CO2, P4

The empirical formula is the simplest whole number ratio of atoms or ions of each element in a compound - Mg, C, NaCl

Relative molecular mass compares the mass of a molecule with the mass of an atom of carbon-12

Relative formula mass compares the mass of a formula unit with the mass of an atom of carbon-12

Water of crystallisation is water molecules that are bonded into a crystalline structure of a compound

Hydrous- contains water molecules Anhydrous- does not contain water molecules

Moles (mol) = concentration (mol/dm3) x volume (dm3)

Avogradro’s law states that equal volumes of gases at the same temperature and pressure contain an equal number of moles

Moles (mol) = volume (dm3) / molar gas volume (24dm3/mol)

The ideal gas equation is: pressure (Pa) x volume (dm3) = moles (mol) x gas constant (8.31 J/mol/K) x temperature (K)

To be an ideal gas, gases must: - have no forces between particles - have a negligible size of particles

Why we don’t get 100% product yield: - reaction may not go to completion - other reactions may have taken place - purification may result in loss of product

Percentage yield = actual yield / theoretical yield x 100

Limiting reagent and reagent in excess: - one reactant is usually in excess (more of it than needed) - limiting reactant will be used up and once done the reaction will stop - limiting reactant determines how much product will form

Atom economy measures how well atoms of the reactants have been put to use - assumes 100% yield - products of which are not desired and have to be disposed of are called waste products - products which are not desired but can be sold or utilised elsewhere are called by-products

Atom economy = molar mass(es) of desired product(s) / molar masses of all products

Atom economy should be improved because: - improves efficiency of process - reduces waste - preserves raw materials - increases sustainability (meeting the needs of today without compromising the ability for future generations to meet their needs)