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chemistry aqa a-level
C2 amount of substance
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Cards (22)
relative atomic mass is the
average mass of an atom of an element, relative to 1/12 the mass of a carbon-12 atom
relative molecular mass is the
average mass of a molecule, relative to 1/12 the mass of a carbon-12 atom
relative formula mass
is the
relative mass of an ionic compound as this does not exist as a molecule
the
avogadro constant
is the number of atoms/particles in
one mole
of a substance
the
avogadro
constant is
6.022 x 10^23
a mole is the
amount of substance that contains 6.022*10^23 atoms/particles
moles = mass /
Mr
concentration
represents
how much solute is dissolved in a known volume of solution
, it is measured in
moldm^-3
concentration =
moles
/
volume
the ideal gas equation is
pV=nRT
in pV=nRT:
p =
pressure
in
Pa
V =
volume
in
m^3
n =
number
of
moles
R =
gas constant
,
8.31
T =
temperature
in
K
no gases
obey
the
ideal gas equation
exactly, so
no real gases are ideal gases
the
empirical formula
is the
simplest whole number ratio of atoms of each element in a compound
to find empirical formula, draw a table:
first row write
masses
or
percentage
by
mass
second row write
Mr
third row use
moles
=
mass
/
Mr
to write
moles
fourth
row divide by the
smallest
scale up
to get
integers
the
molecular formula
is the
actual number of atoms of each element in a compound
to find the
molecular formula
, divide the
Mr
of the compound by the Mr of the
empirical formula
, then
multiply
the
empirical formula
by this value
chemical equations
need to be balanced
before you can use them in calculations
rules for balancing equations:
do not change any of the formulae
only add coefficients, no other numbers
coefficient represents number of moles of that substance
if the equation is ionic, the charges on each side must also be balanced
atom economy = (
mass of desired product
/
total mass of reactants
) *
100
a
high atom economy
means
less waste
is produced, making it
more economically viable
percentage yield = (
experimental yield
/
theoertical yield
) *
100
a
high percentage yield
means
less product
has been
lost
throughout the
manufacture process