Download Moles Chemistry Knowledge Organiser Unit 3

Chemistry Knowledge Organiser
Unit 3 - Chemical Quantities and Calculations Knowledge
Organiser
Equations must be BALANCED. This
means that big numbers are put IN
FRONT of the formulae to balance them.
The following equation is not balanced:
Mg + O2  MgO
What to do next?
Make a table like this:
Reactants
Products
Mg = 1
Mg = 1
O =2
O = 1
You can see that the oxygen is not
balanced – you need another O atom in the
products so just multiply it by 2:
Mg + O2  2MgO
BUT there are now 2 MgO on the
products side which means that there are
now 2 Mg atoms. Just go back to the
reactants side and multiply the Mg by 2:
2Mg + O2  2MgO
Done!
Moles are a measure of how much
chemical you have. One mole of a
substance is its atomic or molecular mass in
grams:
Formula mass (MR) = the relative atomic
masses of all the atoms in a formula e.g.
formula mass for H2O = 1 + 1 + 16 = 18.
‘Excess’ means you have more
than you need of a chemical.
‘Limiting Reagent’ means you
have a limited amount of a
chemical and it will run out first.
Moles
When the
mass of
products is
MORE than
the reactants,
the mass has
been gained
from the
atmosphere
around e.g.
heating a
metal in
oxygen to
make a metal
oxide.
Chemistry Knowledge Organiser
Unit 3 - Chemical Quantities and Calculations Knowledge Organiser
Moles in Equations
In equations, the large numbers in
front of the formulae show how many
molecules are reacting, but also can
be used as the number of moles
aswell.
Moles can be used to predict masses
from equations.
Looking at the example on the left, if
only 6g of carbon was burned then
you only need half the amount of
oxygen and half the carbon dioxide
would be produced. How many grams
of CO2 would be produced?
Concentration of solutions – keywords:
Solute
Solvent
Solution
Concentration
v must be in litres not cm3.
(1litre = 1000 cm3)
Example calculation:
what is the
concentration of a solution containing 2
moles of solute in a volume of 100cm3?
Answer: use equation c=n/v
n= 2, v= 100/1000 = 0.1, c=2/0.1 = 20
moles/dm3.
Good atom economy
reduces waste and is
what chemical factories
try to achieve.