Molecular mass of a molecule is the sum of the atomic masses of individual atoms in it. i) Find the molecular mass of Na2CO3 .

Question

Read the following information and answer. 

Molecular mass of a molecule is the sum of the atomic masses of individual atoms in it.

Element	Atomic number	Atomic mass
Sodium	11	23
Oxygen	8	16
Hydrogen	1	1
Carbon	6	12

i) Find the molecular mass of Na₂CO₃ .

ii) If the molecular weight of a compound is 44. Which is made with carbon and oxygen. What its molecular formula?

iii) What is the unit of atomic mass?

iv) On the basis of molecular weights of NaOH and H₂O, which is heavier?

Answer 1

i) Molecular mass of Na₂CO₃ = (23 × 2) + 12 + (16 × 3) = 46 + 12 + 48 = 106

ii) Molecular weight of a compound = 44 

At. mass of Carbon = 12 Remaining at. mass = 44-12 = 32 = 16 × 2 

Hence, 16 × 2 ⇒ (Oxygen atomic mass × 2) ⇒ O₂ 

Molecular formula = CO₂

iii)  Unit of atomic mass = amu

atomic mass unit (amu) is defined as precisely \(\frac{1}{12}\)the mass of an atom of carbon -12.

iv) Molecular weight of NaOH = 23+16 + 1= 40 

Molecular weight of H₂O = (1 × 2)+ 16 = 2 + 16=18

Hence, NaOH is heavier than H₂O.