How do you do the following empirical formula questions?

Question

1.What is the empirical formula of a compound that is 32.48% sodium, 22.65% sulfur, and 44.99%? Also name this compound.

2. Analysis of a 10.150 g sample of a compuound known to contain phosphorus and oxygen indicates a phosphorus content of 4.433 g.

a. What is the empirical formual of this compound?

B. The molar mass of this compound is 238.89 g/mol. What is the compound's molecular formula?

Answer 1

We consider 100 g of this compound :

Moles Na = 32.48 g / 22.9898 g/mol = 1.413

Moles S = 22.65 g / 32.066 g/mol =  0.7064

Moles O ( I presume) = 44.99 / 15.9994 = 2.812

we divide by the smallest number

1.413 / 0.7064 = 2 => Na

0.7064 / 0.7064 = 1 => S

2.812 / 0.7064 = 4 => O

Na2SO4 sodium sulphate

Mass P = 10.150 - 4.433 = 5.717 g

Moles P = 5.717 g / 30.9738 g/mol = 0.1846

Moles O = 4.433 / 15.9994 g/mol = 0.2771

0.1846 / 0.1846 = 1 => P

0.2771 / 0.1846 = 1.5 => O

to get whole numbers we multiply by 2

P2O3 => empirical formula ( molar mass = 109.94 g/mol)

238.89 / 109.94 = 2

P4O6 is the molecular formula