Unit 1 –Amount of Substance
The Mole
A mole is just a very large number of particles.
Amount of substance can be measured using a unit called the mole
(mol).
One mole = 6.02 x 1023 particles = Avogadro Constant
Particles = atoms, molecules, electrons, ions
1 mole of substance has a mass equal in ‘g’ to its formula mass
Mr = Compound Mass
Ar = Elements Mass
The mole is a useful quantity because one mole of a substance
always contains the same number of entities of the substance.
An amount in moles can be measured out by:
- mass in grams
- volume in dm3 of a solution of known concentration
- volume in dm3 of a gas.
Example: 1 mole of carbon = 6.02 x 1023 atoms
1 mole of methane = 6.02 x 1023 molecules
1 mole of sodium = 6.02 x 1023 ions
1 mole of electrons = 6.02 x 1023 electrons
Number of particles = Number of moles x Avogadro’s constant
The amount of a substance in moles can be calculated from
MASS and Mr
Number of moles = Mass of substance / Mr
1. 1 mole of any substance has a mass that’s the same as its
relative molecular mass – Mr in grams.
Example: the Mr of water = (1 x 2) = 2 + 16 = 18g
2. You can work out how many moles of a substance you have
from the mass of the substance and its relative molecular
mass – Mr.
Number of moles = Mass of Substance / Mr
, The concentration of a solution is measured in mol dm -3
The concentration of a solution is measured is how many moles are
dissolved per 1dm3. The units = mol dm-3
Number of moles = Concentration x Volume
Concentration = mol dm-3
Volume = dm3
1dm3 = 1000cm3
From cm3 to dm3 divide by 1000
Ideal Gas Equation
The ideal gas equation lets you find the number of moles in a
certain volume of gas.
pV = nRt
p = pressure - Pa
V = volume – m3
n = number of moles
R = 8.31 J K-1 mol-1
T = temperature – K
1cm3 = 1 x10-6 m3
1dm3 = 1 x 10-3 m3
The ideal gas equation shows that any gas will give the same
volume for pressure exerted as long as there are equal moles of
each gas. This is because in an ideal gas, we would consider
particles to be at infinite separation. E.g to have no influence on
each other, => this also applies to any mixture of gas.
Empirical and Molecular Formula
Empirical formula = The simplest whole number ratio of atoms of
each element in a compound.
The empirical formula has a mass which can be used along with
mass spectrometer data to determine the molecular formula.
Molecular formula = The actual number of atoms of each element
in a compound. It is made up of a whole number of empirical units.
Empirical Formulas can be calculated from the percentages of the
different elements it contains.
Empirical formulas can be calculated from experiments.
The Mole
A mole is just a very large number of particles.
Amount of substance can be measured using a unit called the mole
(mol).
One mole = 6.02 x 1023 particles = Avogadro Constant
Particles = atoms, molecules, electrons, ions
1 mole of substance has a mass equal in ‘g’ to its formula mass
Mr = Compound Mass
Ar = Elements Mass
The mole is a useful quantity because one mole of a substance
always contains the same number of entities of the substance.
An amount in moles can be measured out by:
- mass in grams
- volume in dm3 of a solution of known concentration
- volume in dm3 of a gas.
Example: 1 mole of carbon = 6.02 x 1023 atoms
1 mole of methane = 6.02 x 1023 molecules
1 mole of sodium = 6.02 x 1023 ions
1 mole of electrons = 6.02 x 1023 electrons
Number of particles = Number of moles x Avogadro’s constant
The amount of a substance in moles can be calculated from
MASS and Mr
Number of moles = Mass of substance / Mr
1. 1 mole of any substance has a mass that’s the same as its
relative molecular mass – Mr in grams.
Example: the Mr of water = (1 x 2) = 2 + 16 = 18g
2. You can work out how many moles of a substance you have
from the mass of the substance and its relative molecular
mass – Mr.
Number of moles = Mass of Substance / Mr
, The concentration of a solution is measured in mol dm -3
The concentration of a solution is measured is how many moles are
dissolved per 1dm3. The units = mol dm-3
Number of moles = Concentration x Volume
Concentration = mol dm-3
Volume = dm3
1dm3 = 1000cm3
From cm3 to dm3 divide by 1000
Ideal Gas Equation
The ideal gas equation lets you find the number of moles in a
certain volume of gas.
pV = nRt
p = pressure - Pa
V = volume – m3
n = number of moles
R = 8.31 J K-1 mol-1
T = temperature – K
1cm3 = 1 x10-6 m3
1dm3 = 1 x 10-3 m3
The ideal gas equation shows that any gas will give the same
volume for pressure exerted as long as there are equal moles of
each gas. This is because in an ideal gas, we would consider
particles to be at infinite separation. E.g to have no influence on
each other, => this also applies to any mixture of gas.
Empirical and Molecular Formula
Empirical formula = The simplest whole number ratio of atoms of
each element in a compound.
The empirical formula has a mass which can be used along with
mass spectrometer data to determine the molecular formula.
Molecular formula = The actual number of atoms of each element
in a compound. It is made up of a whole number of empirical units.
Empirical Formulas can be calculated from the percentages of the
different elements it contains.
Empirical formulas can be calculated from experiments.
