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IGCSE
Chemistry
Stoichiometry
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Indrayani Mondkar
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Cards (19)
Valency
The amount of electrons an atom has to gain or lose in order to achieve a
full outer shell
Valency
Groups
1-3
(metals) will
LOSE
electrons
Groups
5-7
(non-metals) will
GAIN
electrons
Group
4
can do either
Ion
An atom that has
lost
or
gained
electrons, resulting in a
charge
Determining chemical formula
1. Know the
valencies
of the
atoms
2. Swap the
numbers around
3. Cancel out if
valencies
are
equal
Word equation
Chemical
equation written in
words
Symbol equation
Chemical
equation represented by
symbols
, must be
balanced
Balancing chemical equations
1. Ensure
same number
of each type of atom on
both sides
2. Cannot change
original
chemical formula
3. Add
numbers
in
front
of reactants/products
State symbols
Represent
the
physical state
of
reactants
/
products
Mole
6.02
x
10
^
23
atoms,
molecules
or
ions
of a
substance
Mole equations
Moles
= Mass / Relative formula mass
Volume =
Moles
x
24
dm3/mol
Concentration =
Moles
/
Volume
Relative formula
mass
(
Mr
)
Sum
of all the different
relative atomic masses
(
Ar
)
Calculating mass from moles
1. Write
balanced
equation
2. Calculate
moles
of
reactant
3. Calculate
moles
of
product
4. Calculate
mass
of
product
Calculating volume from moles
1. Calculate
moles
of
gas
2. Use
mole equation 2
to find
volume
Calculating volume from mass
1. Calculate
moles
of
gas
2. Use
mole equation 2
to find
volume
Calculating volume of reactant from volume of product
1. Use
balanced
equation to find
mole
ratio
2. Calculate
moles
of reactant
3. Use
mole
equation 2 to find
volume
of reactant
Calculating percentage yield
Actual
yield /
Theoretical
yield x
100
Calculating percentage purity
Mass
of
pure substance
/
Total mass
x
100
Empirical formula
Simplest whole number
ratio
of
atoms
in a
compound
Molecular formula
Actual number
and
type
of
atoms
in a
compound