4.4 MOLES I Flashcards
Define Relative Atomic Mass
- The weighted average mass of the isotopes of an element
- It is measured on a scale on which a carbon-12 atom has exactly 12 unit
Define Relative Molecular Mass
- The total average mass of one molecule of a compound
- Atoms which are compared to 1/12th of one atom of Carbon-12
Symbol for Relative Atomic Mass
Ar
Symbol for Relative molecular mass
Mr
How do you work out the Mr of a substance
- If a word compound, find the formulae
- Break each atom in the substance down to it’s Ar
- Add up the ammounts
Unit for Ar/Mr
No unit
What is Avogadro’s constant
6.022 x10^23 atoms/molecules
Symbol for Avogadro’s constant
NA
How to calculate the number of molecules in a certain amount of a substance
Amount of any substance (in moles) x Avogadro’s Constant
Equation for composition of substances
% of Substance = Ar of substance / Mr of Compound x100
What should be done before the equation if working out the composition of a substance that is a word formulae
Convert it into a molecular formula
What does a mole represent
How many particles of substance there are
Formulae for Moles
Moles = mass (g) / Ar or Mr
Formulae for mass (g)
Mass (g) = Moles x Mr or Ar
What must you do to a substance where the mass ISN’T in grams
Convert it FIRST