1.7 Quantitative Chemistry

Mass of products =

The mass of the reactants

Balanced symbol equation

equal numbers of each type of atom on either side of equation

Relative atomic mass

weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12

Relative mass of carbon-12

12

Relative formula mass

The relative atomic masses of the elements in a compound added together

Theoretical yield

maximum amount of product that can be made

Actual yield

The amount of product made by carrying out the reaction

Percentage yield equation

Actual yield/theoretical yield x 100

Reasons % yield is less than 100%

Reversible reaction, product is lost, side reactions

Reversible reaction

A chemical reaction in which the products re-form the original reactants

Ways product is lost

Stuck in the reaction vessel, or by separation from the reaction mixture

Side reactions

Reactions that do not give the desired product of a reaction

Use of percentage yield

To measure the efficiency of a reaction

Molecular formula

A chemical formula that shows the number and kinds of atoms in a molecule, but not the arrangement

Empirical formula

a chemical formula showing simplest ratio of elements in a compound

Hydrated

A crystal containing water molecules

Anhydrous

A crystal which doesn't contain any water molecules

Heating to constant mass

Heating and weighing, and repeating this until two readings are the same

Thermal decomposition

The breakdown of a compound by heat

Determining waters of crystallisation

Heat hydrated compound to constant mass

Mole

Avogadro's number of an atom, ion or compound

Formula for moles

Mass(g)/relative formula mass (Mr)

The mass of 1 mole of any substance=

formula mass in grams

mol

Symbol for moles

Value of Avogadro constant

6.02 x 10^23

Avogadro's constant

The number of atoms, molecules or ions in a mole of a given substance

Relative atomic mass

The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12.

Relative formula mass

The relative atomic masses of the elements in a compound added together

Reacting mass

The amount of one reactant needed to react exactly with another reactant.

Link between moles and equations

Multipliers show you the ratio of moles in a reaction

Reagent

Reactant

Limiting reactant (limiting reagent)

A reactant that is totally used up so it determines the amount of product formed.

Excess

More than is required to react with the limiting reactant

1 kg

1000 g

1 tonne

1000 kg