M2 Amount of Substance Flashcards
What is Avogadro’s constant
One mole of a substance contains 6.02 x 10 23 particles.
One mole of a substance = mr
Define molar mass and give the unit
The mass per mole of a substance g/mol
How to calculate number of moles?
Mass ÷ mr
Define empirical formulae
The simplest whole-number ratio of atoms of each element in a compound
Define relative molecular mass (Mr)
Comparing the mass of a molecule with the mass of an atom of carbon-12
Define relative formula mass
Comparing the mass of a formula unit with the mass of an atom of carbon-12
Describe hydrated salts
- Water molecules are part of hydrated salts crystalline structure.
- When blue crystals of hydrated copper sulfate are heated, bonds holding the water within the crystal are broken and the water driven off, leaving a whole anhydrous copper sulfate.
What assumptions have to be made to calculate the formula of a hydrated salt by reacting masses?
- All of the water has been removed
- No further decomposition has occurred (as many salts decompose further when heated)
Compare dm3 and litres
1 dm3 = 1000cm3 = 1000ml = 1l
1 cm3 = 1 ml
How to convert between moles and volumes
Moles = concentration (mol/dm3) x volume (dm3)
How to convert grams/dm3 into moles/dm3
Use mass ÷ mr = number of moles
What is standard solution?
A solution of a known concentration, often 1 mol/dm3
Standard solutions are prepared by dissolving an exact mass of the solute in a solvent and making the solution to an exact volume.
Define molar has volume
The volume per mole of has molecules at a stated temperature and pressure, usually RTP.
At the same temperature and pressure, equal volumes of different gases contain the same number of molecules.
What is RTP?
20° Celsius and 101 lapa pressure
At RTP 1 mole of gas has a volume of 24dm3
How to convert between moles and gas volumes (RTP)
Moles = volume ÷ 24
What is the ideal gas equation?
pV = nRT
pressure (Pa) x volume (m3) = moles x ideal gas constant (8.31) x temperature (K)
How to convert cm3 to m3?
x 10 *-6
How to convert dm3 to m3?
x 10 *-3
How to convert degrees Celsius to degrees kelvin?
+ 273
How to convert kPa to Pa?
x 10*3
x 1000
What is percentage yield?
(Actual yield ÷ theoretical yield) x 100
Why is percentage yield never 100%?
- Incomplete reactions
- Product loss during practical preparation/purification
- Unwanted side reactions occurring
What is the limiting reagent?
The reactant that is not in excess and will be completely used up first and stop the reaction.
What is atom economy?
- A measure of how well atoms have been utilised
- atom economy = (mr of desired products ÷ mr of all products) x 100
Why is a high atom economy important?
- Reactions produce a high proportion of desired products and few unwanted waste products
- High atom economy is important for sustainability as they make best use of natural resources
What is the ratio of moles in an equation
The stoichiometry of the reaction
