Chapter 4 Flashcards
relative atomic mass, Ar
the average mass of naturally occurring atoms of an element on a scale where the 12C atom has a mass of exactly 12 units
relative molecular mass, Mr
the sum of the relative atomic masses
mole
The unit representing the amount of ions, atoms or molecules in a substance
Avogadro constant
The number of atoms, molecules or ions in a mole of a given substance, 6.02 x 10^23
the molar gas volume
24 dm3 at room temperature and pressure
Calculate empirical formulae
using molecular mass ATOMIC MASS IS ONE, THEREFORE 2H2O IS 2+16 NOT 4+16:
- Add the total atomic masses of 2 substances
- Find the mass ration by dividing one mass by the total (e.g magnesium = 24, Oxygen = 16, 24/30)
- Divide the mass ratio by the atomic mass (e.g 60/24)
- Put the ratio of the two elements in their simplest form. (e.g 2.5:2.5 = 1:1)
Calculate percentage yield
actual yield/ theoretical yield * 100
Find the theoretical yield by dividing the initial mass by the molecular mass and multiplying it by the molecular mass of the product. Find if the number of moles is proportional for the reactant as well as the product (e.g 2Ca and 2CaO have the same number of moles). Actual yield will be told.
Calculate molecular formulae
calculate the molecular mass of the empirical formula, divide the molecular mass by the mass of the empirical formula, multiply the numbers in the empirical formula by this value.
Calculate percentage purity
mass of pure product/ mass of impure product * 100
Concentration
Mass (g) / Volume solvent (dm^3)
Molar concentration
Number of moles/ volume solvent (dm^3)
Number of particles
number of moles * avagadros constant
Mole
mass (g) / Molecular mass
Volume
Mass (kg) / density (kg/dm^3)
Mole (gas)
Volume (dm^3) / 24 (dm^3/mol)
