(i) Calculate the formula unit mass of Na2CO3.
[given atomic mass of Na = 23 u, C = 12 u and O = 16 u]
(ii) What is the mass of one mole of oxygen atoms?
(iii) Convert 12g of oxygen gas into mole, if atomic mass of oxygen is 16 u.
(i) Formula unit mass of Na2CO3:
2 × (Atomic mass of Na) + atomic mass of C + 3 × (Atomic
mass of oxygen)
⇒ 2 × 23 + 12 + 3×16
⇒ 46 + 12 + 48
⇒ 106u
(ii) To calculate the mass of 1 mole of oxygen atoms:
By applying the formula given:
Mass of oxygen atoms = Number of moles × Molar mass
⇒ Mass of oxygen atoms = 1mole × 32g/mol
⇒ Mass of oxygen atoms = 32g
Thus, the mass of 1 mole of oxygen atoms is 32g.
(iii) Given: Mass of oxygen = 12g
Atomic mass = 16u
By applying the formula given:
⇒ 
⇒ Number of moles = 0.75mol
Thus, the number of moles = 0.75mol