Topic 7 Quantitative Chemistry Flashcards
Relative atomic mass
The mass of the atom compared with that of the carbon 12 isotope, which has a mass of exactly 12 and it is the weighted mean mass of the mass numbers
Relative formula mass/ relative molecular mass/ molar mass
The sun of the relative atomic mass of all the atoms present in the formula of a substance
How to calculate Mr
Add all masses together, multiplying by the power when needed
How to calculate percentage of an element in a compound
Mass of element in one mole of compound / mass of one mole of the compound x 100
Mole
An amount of a chemical. The Mr of a substance in grams is known as one mole of that substance
How to calculate the mass of one mole of a substance
Mr (masses added together)
Mole equation (including rearranged)
n = m / Mr
m = n x Mr
Limiting reactant
The one that runs out first
How to calculate percentage yield
Actual yield / theoretical yield x 100
How to calculate reacting masses
Divide known mass by the Mr of its compound/element to get its moles, apply ratio, multiply by the unknown compound/element’s Mr
Why is the percentage yield less than 100%?
Incomplete reaction
Impossible to separate product fully out of the reaction mixture
Reaction is reversible and may not go to completion
As a result of a side reaction
Empirical formula
The simplest whole number ratio of the atoms of each element in a compound
Molecular formula
Actual number of atoms of each element in a molecule
Hydrated
Solid crystals contain water of crystallisation
Anhydrous
Does not contain water of crystallisation
Water of crystallisation
Water that is chemically bonded into the crystal structure
How can water of crystallisation be removed?
Heating to constant mass
What is heating to constant mass?
Reheating and reweighing until a constant mass is observed. This ensures that all the water of crystallisation has been removed from the hydrated crystals
How to calculate the percentage of water of crystallisation in a compound
Total Mr of water / total Mr of compound x 100
How to calculate the relative formula mass of compounds containing water of crystallisation
Eg finding the x. Make a table for the compound and its woc. Figure out mass, Mr, therefore moles (divide) and the ratio will equal x (when simplified to 1:__)
