Please enable JavaScript.
Coggle requires JavaScript to display documents.
Moles review - Coggle Diagram
Moles review
Relative formula mass
Symbol - Mr
Relative atomic mass
found on periodic table
Average mass of atoms compared to the mass of carbon -12 atom.
Symbol - Ar
Can be used to help us find relative formula mass
Mr of a compound is the sum of atomic masses in a formula.
Percentage mass by composition
Example find percentage of C in CO2
Mr = 44. C = 12
12/44 X 100 = 27% carbon
The rest is oxygen
The percentage by mass of an element in a compound tells us what mass of a particular compound is due to a particular element.
Moles and Avogadro's constant.
One mole of a substance = Its Ar / Mr in grams
Example
1 mole of
Mg=24g
1 mole of
O2 = 32 g
Way of measuring out a known number of atoms / molecules
Allows us to make sure that there will be enough quantities of each reactant.
Mass = Mr X Moles
Example
Calculate mass of 3 moles of CuSO4
CuSO4 Mr = 159.5 X 3 = 478.5g
6.02 X 10 23
One mole of a substance contains this many atoms/ molecules
If you have more/fewer moles you can multiply by this number to work out the number of particles.
Balancing equations using moles
Steps to balancing equations.
Step 1
Write word equations so you are aware of the reactants and products.
Step 2
Get formulae right using periodic table.
Step 3
Add only big numbers to make the number of atoms on each side balanced.
Extended method.
1
Symbol equation.
2
Write masses.
3
Write mass of 1 mole.
4
Calculate number of moles.
Moles = Mass / Mr
5
Ratio
6
Write balance equation using ratio.
Reacting masses
conservation of mass
Atoms are not created or destroyed. Mass of reactants and products are always equal.
As we know this we are able to predict the mass of a product if we know the masses of the reactants.
Thermal decomposition
Reactions that involve breaking compounds down using heat.
May make it look like products mass has decreased. However, it may have just escaped in the form of gas.