✅5 - Formulae, Equations and Amounts of Substance
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What are amounts of substance measured in?
Moles (mol)
What does one mole contain?
A standard number of atoms, molecules or ions
What is the relative atom mass?
The average mass d an element relative to 1/12th if the mass of an atom of carbon12.
What is molar mass (Mr)?
The mass of one mole of a chemical with the unit g mol-1.
How would you work out the molar mass of a molecule?
Add up the relative atomic masses of all the atoms in the molecule
How do you work out the amount of substance in moles?
mass/ Mr
What is a species?
A collective noun to refer generally to atoms, molecules or ions
What is the Avogadro constant?
The number of atoms, molecules or ions in one mole of a substance. 6.02 x 10^23 mol-1
How would you work out the number of particles?
n x Avogadro
What is the empirical formula?
The simplest whole number ratio of the atoms of different elements in a compound
How would you work out the empirical formula?
• Write down the actual mass of each element • Write down the molar mass of each element • Divide the actual mass by the molar mass for each element • Divide all the numbers by the smallest one • See ratio
What is molecular formula?
The total number of atoms of each element in the molecule
What is percentage composition?
The percentage by mass of each of the elements in a sample of a compound
How would you work out the empirical formula from percentages?
Turn each percentage into grams and assume the total mass of the compound is 100g
What is the ideal gas equation?
pV = nRT
1 atmosphere =
100,000 Pa
1 bar =
100k Pa (100,000Pa)
To convert °C into K…
… +273 to the number
To convert K into °C
Take away 273 from the number
1m^3 =
1000dm^3 (1,000,000cm^3)
R=
8.31JK-1mol-1
What most the units be in the ideal gas equation?
P = Pa V = m^3 n = moles T = Kelvin
The gas laws state that the volume of a gas depends on what three things?
• The temperature • The pressure • The amount of gas in moles
What could the ideal gas equation be used for?
Measuring the molar masses of gases in the days before mass spectrometry