C4: Chemical calculations
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What is the Law of Conservation of Mass
Atoms cannot be created or destroyed
Why is that
Total mass of reactants is the total mass of products
How do we calculate the relative atomic mass of an atom
Find the atomic mass of the compound
How do we balance a chemical equation
Before and after a reaction, there must be the same number of atoms of each element
Is this balanced? H2 + 02 = H20
That is unbalanced as although the hydrogen is fine, we need one more oxygen
Is this balanced? H2 + 02 = 2H20
This balances the oxygen, however we would have too much hydrogen atoms. So that is still unbalanced
Is this balanced? 2H2 + 02 = 2H20
Yes that is as there are 4 hydrogens and 2 oxygens on both sides
What is the molecular formula
The actual amount of atoms making up a molecule Eg: C6H1206. This is glucose
What is the empirical formula
The simplest ratio of atoms that make up a molecule CH20
What is a mole
A mole is a measure of chemical amounts
What is the Avogadro Constnant
Shows that 1 mole of a substance is 6.02 X 1023 atoms of that substance
How do we calculate relative formula mass of a substance
It is equal to the mass of 1 mole of the substance. This is the same as relative atomic mass for an element
Prove this
The mass of 1 carbon mole is 12g, which is the same ass the atomic mass of carbon
Calculate the relative formula mass of carbon dioxide C02
• Work out the AR of Carbon 12 • Work out the AR of one oxygen 16 12 + (16 x 2) = 44
How do we calculate moles
Mass divided by Relative Formula Mass
What is a limiting reactant
When it is completely used up when reaction stops when used up
What should we ensure when neutralising an acid
Theres no leftover acid after the reaction
How can we solve this
Use an excess amount of the other reactant
What is excess
more than neccessary
What is the other equation for moles and what are the measurements
Concentration X Volume Moles = mol Volume = dm cubed Concentration = mol/dm cubed
How do we calculate percentage yield
(real yield/theoretical yield) x 100
How do we calculate atom economy
(relative molecular mass of desired products/total relative molecular mass of all reactants) x 100