Question

A compound consisting of only phosphorous and oxygen atoms is 43.64 % phosphorus by mass.The molecular mass/formula weight of the compound is 283.88 amu. How many phosphorous atoms ar in a molecule of this compound? Please show all calc involved.

Answer 1

First, we calculate the mass of Phosphorous present:
283.88 x 0.4364
= 123.88 amu
Atomic mass of P is 31 amu

moles of P = mass / Ar
= 123.88 / 31
= 4.0 moles

We know that one mole of substance has 6.02 x 10²³ particles
Atoms of P = 4 x 6.02 x 10²³ 
= 2.41 x 10²⁴ atoms