Quantative Chemistry

All Compounds have a relative formula mass

• The relative formula mass (Mr) is just the relative atomic masses (Ar) of all the atoms in the molecular formula added together

You can calculate the % of mass of an element in a compound

• Percentage mass of element= Ar x no. of atoms of that element    x 100
•                                                 Mr of the compound           

One mole of any substance is just an amount of that substance that contains an avogadro number of particles- so 6.02 x 1023 

• One Mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass (Mr) for that substance.
• No. of Moles=   Mass in g
•                            Mr           

 The mole is simply the name given to an amount of a substance

In a Chemical Reaction Mass is always Conserved

• During a chemical reaction no atoms are destroyed and no atoms are created
• This means there are the same no. of and types of atoms on each side of the reaction equation.  

If the mass seems to change there's probably a gas involved

• If the mass increases, its probably because one of the reactants is a gas thats found in air and all the products are solids, liquids or aqueous.
• If the mass decreases, its probably because one of the products is a gas and all the reactants are solids, liquids or aqueous.

You can use Moles to calculate Masses in equations

• The big numbers in front of the chemical reactants and products in a balanced equation tell you how many moles there are.

 You Can use this formula to work out mass/moles or formula of atomic mass with the below method:

1. Fill in grid with the data from the question (Grid should consist of balanced equation, then mass in g, then Ar/Mr and then moles) 

2. Calculate formula mass of each compound

3.Calculate Number of moles of known value

4.  Use a ratio to find unknown moles

5.Calculate unkown mass

Or

1. Ignore any big numbers and fill out Ar/Mr row

2. Work out ratio (use big numbers)

3. Work out mass

Or

1. Ignore any big numbers and fill out Ar/Mr row

2. Work out ratio (use big numbers)

3. Work out mass

Reactions stop when one reactant is used up

• Any other reactants that have been left behind are in Excess
• The reactant that's used up is called the Limiting Reactant
• The amount of product formed is Directly Proportional to the limiting reactant
• This is because if you add more reactant there is more reactant particles to take part in the reaction, which means more product particles

Concentration is the amount of substance in one place

• The more solute there is in a solution, the more concentrated the solution

Solute is the substance dissolved

Solvent is the substance that dissolves a solute

Concentration can be measured in g/dm3

• Concentration= mass of solute(g)
•                           volume of solvent (dm3)