Question

In 84.7g magnesium hypophosphite:

1. What is the number of total number of atoms?

2. How many moles of oxygen?

Answer 1

magnesium hypophosphite = Mg₃(PO₂)₂

Molar mass of magnesium hypophosphite = 198.86 g/mole

Thus, moles of magnesium hypophosphite in 84.7 g of it = mass/molar mass = 0.426

Now, 1 molecule of magnesium hypophosphite contains 3 Mg, 4 O & 2 P atoms

Thus, a total of 9 atoms are present in 1 molecule of magnesium hypophosphite

Therefore in 1 mole of magnesium hypophosphite, 9 moles of atoms are present

or, in 0.426 moles of magnesium hypophosphite, 3.834 moles of atoms are present = 3.834*6.022*10²³ = 2.309*10²⁴ atoms are present

Now, 1 mole of magnesium hypophosphite contains 4 moles of O-atoms

Thus, 0.426 moles of magnesium hypophosphite contains 1.704 moles of O atoms

Thus, moles of O₂ = 0.5*moles of O-atoms = 0.852