What is the formula for the amount of moles a substance has?
Amount (mol) = mass / mr
How do you work out the mass of an element in a compound?
%of Element in Ar of element in compound
the compound = _________________________________ X 100
Mr of the compound
What is the empirical formula?
Simplest whole number ratio o Fatima of each element
What is the molecular formula?
Shows all of the atoms of each element grouped together
How do you work out the empirical formula of a compound?
- For each element you divide the mass by the Ar, to get the amount in moles
- You then divide them all by the smallest
- Then you have the simplest ratio
How do you convert empirical formula into molecular formula?
- Work out the empirical formula mass
- Divide the relative formula mass by the empirical mass
- Multiply the empirical formula by the answer to part 2
How do you work out a reacting mass calculation?
- Work out the amount in moles of the substance you are given the information for
- Work out the amount in moles of the other substance using the equation
- Work out the mass of the other substance
E.g What mass of Iron is produced when 32kg of iron oxide is heated with CO?
Fe2O3 + 3 CO -> 2 Fe + 3 CO2
- Amount of Iron Oxide = 32000/160 = 200
- 1 mole of iron oxide is equal to 2 moles of iron. Therefore amount in moles of iron = 400 mol
- Mass of iron = 400 X 56 = 22,400g
How much does 1 mole of gas occupy?
24,000 cm3 or 24 dm3
How do you work out the volume of a substance?
- Work out the amount in moles of the substance you are given the information for
- Work out the amount in moles of the other substance using the equation
- Work out the volume of the other substance
E.g What volume of oxygen is required for the complete combustion of 11.5 g of sodium?
4 Na + O2 —> 2 Na2O
- Moles of Na = 11.5/23 = 0.5
- Moles of O2 = 0.5/4 = 0.125
- Volume of O2 = 0.125 X 24 = 3 dm3
