2.1.3 Amount of substance Flashcards
define the term amount of substance
- a quantity to count number of particles in substance
- measured in unit called mole (mol)
define the term mole
- the unit for amount of substance
- 1 mole is the amount of substance that contains 6.02 x 10*23 particles
define the term Avogadro constant
- N
- the number of particles per mole
- 6.02 x 10*23
define the term molar mass
- M
- links moles with mass
> it’s the mass per mole of a substance - units are gmol-1
give the formula for calculating molar mass
moles = mass / mr
- mr = mass / moles
define the term molar gas volume
- the volume per mole of a gas
- units are dm3mol-1
- at room temp + pressure the vol is approx 24.9 dm3mol-1
give the formula to calculate the molar gas equation at room temp + pressure
volume (dm3) = amount of gas (moles) x 24
what is an empirical formula
- the simplest whole number ratio of atoms of each element present in a compound
describe the steps needed to calculate the empirical formulae of a compound
- divide the amount (g) of each element by molar mass - gives you molar ratio
- divide the answer of each element by smallest number
what is molecular formula
- the number and type of atoms of each element in a molecule
how would you calculate the molecular formula of a compound
- you would divide the relative molecular / formula mass (given) by the empirical formula mass (total mr) to give the number of units of that compound in a molecule
- you would multiply that number by the compound to get the molecular formula
define the terms anhydrous + hydrated
- anhydrous = without water
- hydrated = with water
what is water of crystallisation
- many crystals are hydrated meaning they contain water molecules as part of their crystalline structure
- the water is known as the water of crystallisation
what are hydrated salts
- salt crystals containing waters of crystallisation
every hydrated salt contains ……. of water molecules
- a specific number
what are the assumptions of water of crystallisation
- how accurate is an experimental formula / how pure is it
- all the water has been evaporated
- no further decomposition
what is the formula for working out concentration of solution
- concentration = moles / volume
how can you change concentration from moldm-3 to gdm-3
- multiply your concentration by your mr to get gdm-3
what is molar solutions in relation to concentration
- ‘M’ means molar and refers to a solution with a concentration in moles per cubic decimeter moldm-3
- example:
2 moldm-3 = 2M
what is the formula for the ideal gas equation (give units)
pV = nRT
- p = pressure (Pa)
- V = volume (m3)
- n = amount of gas molecules (mol)
- R = ideal gas constant = 8.31 Jmol-1K-1
- T = temperature (K)
what is the theoretical yield
- maximum possible amount of product
why is it difficult to achieve 100% in a percentage yield
- reaction may not have gone to completion
- side reactions may occur, leading to by-products
- reactants may may not be pure
- some of reactants / products may be left behind in the apparatus
- separation + purification may result in loss of some product
what is the formula for percentage yield
- percentage yield = (actual yield / theoretical yield) x 100
what is atom economy
- a measure of how well atoms have been utilised
> describes the efficiency of a reaction in terms of all atoms involved (takes into account all products including waste products)
what is the formula to work out atom economy
atom economy = (mr of desired product / mr of all products) x 100
how can atom economy benefit society
- using processes with higher atom economy companies can reduce amount of waste product
- high atom economy make processes more sustainable as they can be maintained at a productive level without completely using up resources
