AQA Chemistry, Unit 1, Amount of Substance

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Unit 1 ­ Amount of Substance
Formula of Ionic Compounds
H+ Ba2+ Fe3+ Cl- O2-
Na+ Ca2+ Al3+ Br- S2-
Ag+ Cu2+ F- SO42-
K+ Mg2+ I- CO32-
Li+ Zn2+ HCO3-
NH4+ Pb2+ OH-
Fe2+ NO3-
Relative atomic Mass (Ar)
The weighted average mass of an element, taking into account its naturally occurring isotopes,
relative to 1/12th the mass of a carbon-12 atom.
Relative Molecular Mass (Mr)
The sum of all the relative atomic masses of all the atoms in a molecule.
Avogadro's constant is 6.02x1023
One mole of any gas contains this number of particles.
For any kind of particle, the number of grams in one mole is the same as its relative mass
One mole of any gas at room temperature and pressure occupies a volume of 24dm3. This is the
molar volume
Air is only 20% oxygen, so if working out the volume of air you need 5X more air than you would
need oxygen.

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Unit 1 ­ Amount of Substance
Molecular Formula
Gives us the actual number of each type of atom in a molecule
Empirical Formula
The formula used to represent the simplest ration (by mole) of atoms in a compound.
Finding Empirical Formula
Element A B
Mass (g) a X
Mass of 1 mole b Y
number of moles a/b x/y
ratio C/Z Z/Z
n m
Simplest formula AnBm
To work out the molecular formula from empirical formula
Actual RFM .…read more

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Unit 1 ­ Amount of Substance
p = pressure (Pa)
V= volume (m3)
n= number of moles
R= gas constant = 8.31
T=temperature (kelvins)
1 kPa=1000Pa
kPa x 1000 = Pa
1m3 = 1000 dm3 = 1,000,000 cm3
cm3 / 1,000,000 = m3
dm3 /1000 = m3
m3x 1000 = dm3
m3 x 1,000,000 = cm3
number of moles
given mass
gas constant
8.…read more

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Unit 1 ­ Amount of Substance
step one ­ balance equation
step two ­ use mass or conc X vol(dm3) to find the number of moles in the first substance
step three ­ use ration from the equation to find the number of moles in the other substance
step four ­ convert moles to masses, volumes or concentrations
example 1
substance 1 + substance 2 +
1 mole : 1 mole
/ ?
x (RFM) gives y (RFM)
z gives z/x x y
example…read more

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Unit 1 ­ Amount of Substance
You can then work out a percentage yield using
Percentage Yield = actual yield .…read more

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Unit 1 ­ Amount of Substance
The number of significant figure of the result should be equal to that of the quantity that
contains the least number of significant figures.
In General
The uncertainty in a single measurement from an instrument is half the value of the smallest
For example, if a thermometer has 1cm3 division, then the uncertainty would be ±0.5cm3.
For digital instrument
The uncertainty is ±½ of the last resolvable digit.…read more


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