C3 revision April 2015
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Substances can be measured in several ways.
They can be:
◦ Number of grams
◦ Number of particles
◦ Number of moles
I mole is 1 chemical quantity
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The mass of one mole of atoms is equal to the
Relative Atomic Mass number (larger number on
periodic table).
One mole of atoms is equal to the AVEGADRO
number of particles (6.02X1023)
Remember, this is all relative to 12g of carbon-12
(so called relative atomic mass)
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To calculate the number of moles use the
following formulas:
If in
doubt......
(divide by
formula
mass!)
1
a), e)
 2 d), f)
3
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
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Can you do the basics?
Try questions 1b, 3b, 4a, 5b and 6
Then try 2a and b (% mass)
Then 7 (reacting masses)
Then 9 yields and ammonia
(Do the other questions at home as part of
your own revision!)
1. % mass of an element in a compound is
No of that type of atoms x atomic mass x 100%
formula mass
e.g. Calculate %N in ammonia
14/17x100%
2. For reacting mass, use the molar ratios from a
balanced chemical equation
e.g.
2Mg + O2  2MgO
FM
2 x 24 + 32  2 x 40
48 + 32  80
The actual yield is how much useful product is
made in a chemical reaction.
You can calculate predicted (maximum yield)
from the balanced equation.
% yield is
actual yield x 100 %
predicted yield
% yield is ALWAY less that 100%.
Why?
Always the same reasons – learn them!
 Q2
 Q5
You need to know what a titration is for and
the step by step process.
How would you prepare a pure dry sample of a
soluble salt?
You can also use a titration to calculate either
the volume of concentration of one of the
reagents. (You will ALWAYS be given 3 of the
4 things you need.
Use the formula
1.
2.
3.
4.
Calculate number of moles of acid used.
Write balanced equation for reaction.
Using moles of acid information, deduce
number of moles of base required.
Calculate concentration of base.
This process also works the same in reverse.
Q1 and Q2.
Extension, Q8
Try the rest at home.

1 mole of = 24dm3 (at room temperature and
a gas
atmospheric pressure)
A GAS SYRINGE is used to
collect gases during
reactions to allow molar
gas calculations to be
performed
Practice your thinking on reversible reactions.
You need to know that a positive energy
change means endothermic and a negative
energy change means exothermic.
What topics do you need to revise?
 Tests for ions?
 Permanent and temporary hard water with
formulae
 Preparing insoluble salts, two methods of
preparing soluble salts
 Electrolysis and half equations
 Gas calculations
 Haber process
 Organic chemistry - making alcohols,
homologous series, ethanoic acid, esters
 Fats, oils and soaps.