Question

Calculate the number of moles of H2O present in 90g of H2O

Answer 1

A mole of a compound is a number of grams equal to the atomic weight of a molecule of the compound, so for water we have 2 hydrogen atoms and one oxygen, so the atomic weight of water is 1+1+16=18, so a mole of water is 18 grams. We have 90g of water so we have 90/18 = 5 moles of water.

Answer 2

Given: 90 grams of water.

To find: We have to find the number of moles.

Solution:

The chemical formula of water is $H_2O$.

The atomic mass of H is 1 and the atomic mass of the oxygen atom is 16.

The molecular mass of water is 2×1+16=18 grams.

18 grams of water has 1 mole.

Thus 90 grams of water has 90/18=5 moles.

Thus the number of moles of water present in 90 grams of water is 5 moles.