What is the Mass of: (A) 0.2 Mole of Oxygen Atoms (B) 0.5 Mole of a Water Molecule

What is the mass of : (a) 0.2 mole of oxygen atoms (b) 0.5 mole of a water molecule 

(A)

A mole is the mass of a substance containing 6.023 10²³of  particles of that substance. The mole is the SI unit for a substance’s quantity. 

The symbol for it is mol. 

1 mol of carbon-12 has a mass of 12 grammes and contains 6.023 10²³ carbon atoms, 

Given statement – 0.2 mole of oxygen atoms.

Atomic number of oxygen – 8

Molecular mass of oxygen – 16u = 16 g/mol

1 mol Oxygen 16 g/mol

0.2 mol ?

                    = 16g/ mol 0.2 mol = 3.2 g

Therefore, the mass of 0.2 mole of oxygen atoms is 3.2g.

(B)

The given statement – 0.5 mole of a water molecule

Formula of water molecule – H₂O

Molar mass of H₂O = 2(1u) + 1(16u) = 18 u = 18  g/mol

1 mol H₂O 18 g/mol

0.5 mol   ?

          = 18 g/mol 0.5 mol = 9g

Thereofre, the mass of 0.5 mole of water molecule is 9g.