Question

(a) Define gram atomic mass of a substance. How much is the gram atomic mass of oxygen ?
(b) How many moles of oxygen atoms are present in one mole of the following compounds ?

(i) Al₂O₃
(ii) CO₂
(iii) Cl₂O₇
(iv) H₂SO₄
(v) Al₂(SO₄)₃

Answer 1

(a) Gram atomic mass refers to the mass of an element , in one mole of atoms of that substance. It is equal to the gram atomic weight of that element.
Gram atomic mass of oxygen is 16 grams.

(b) Number of moles of oxygen in the listed compounds are as follows:
• Al₂O₃: 3 moles of oxygen are present in 1 mole of Al₂O₃.
• CO₂: 2 moles of oxygen are present in 1 mole of CO₂.
• Cl₂O₇: 7 moles of oxygen are present in 1 mole of Cl₂O₇.
• H₂SO₄: 4 moles of oxygen are present in 1 mole of H₂SO₄.
• Al₂(SO₄)₃: 12 moles of oxygen are present in 1 mole of Al₂(SO₄)₃ (4 × 3 moles).