Molar Mass (M)

Molar mass is the mass of 1 mol of a substance

It could also be thought of as the mass of 6.02 x 10^23 entities

The unit symbol for molar mass is g/mol 

The molar mass of elements is the atomic mass -- just change the unit to g/mol

If we had been talking about the mass of one atom then the unit from the periodic table would have been u (atomic mass unit)

Amount to Number of Entities

Remember that a mol is 6.02 x 1023 entities. So if you know the amount (# of mols) then you can calculate the number of entities.

Mathematically: N (entities) = n (mol) x NA (entities/mol)

Example: a) Determine the number of formula units in 0.563 mol of calcium chloride

b) Determine the number of chloride ions in 0.563 mol of calcium chloride

Given:

n = 0.563 mol

NA = 6.02 x 10^23 ent/mol

N = ?

a)

N = n x NA

N = 0.563 mol x 6.02 x 10^23 fu/mol

N = 3.39 x 1023 fu

b) CaCl2

Every fu of CaCl2 has 2 ions of Cl

Ratio of CaCl2:Cl- is 1:2

NCl- = NCaCl2 x 2

NCl- = 3.39 x 1023 fu x 2 ions/fu

NCl- = 6.78 x 1023 ions of Cl

Summary