Unit 4: The Mole

Avogadro's number

1 mole is 6.02 x 10^23

How to find the number of particles from number of mol

multiply the number of mol by Avogadro's Number/6.02*10^23

How to find the number of mol from a number of particles

divide the number of particles by Avogadro's Number/6.02*10^23

Molar Mass

the mass of one mole of a substance

How to calculate molar mass

addition of atomic mass on periodic table is the molar mass

how to find number of mol from mass and molar mass

n = m/M

law of definite proportions (law of constant composition)

in a given compound, the elements are always present in the same proportion by mass.

empirical formula

the simplest formula

shows the smallest whole number ratio of atom types in a compound

valuable because it leads to the calculation of molecular formulas

How to find empirical formula

a table with these columns: element, mass(g), molar mass, number of moles, ratio

if you are given a percent composition but no total mass then the total mass becomes 100g

50% Na = 50g Na

the Ratio is found by dividing every number of mole number by the smallest number of moles. the ratio must be a whole number, if the ratio number is 1.5 you can double all the ratios to make it work

molecular formula

shows the number of atoms of each element in a compound

ONLY applies to molecules

used to distinguish between compounds because more than one compound can have the same empirical formula