Calculate the molecular masses of H2, O2 | Class 9 Science Chapter Atoms and Molecules, Atoms and Molecules NCERT Solutions

Question:

Calculate the molecular masses of H2, O2, Cl2, CO2, CH4, C2H6, C2H4, NH3, CH3OH.

Answer:

Atomic mass includes the masses of three subatomic particles which make up an atom i.e. proton, neutron and electron.

Unit of atomic mass is 'u'

‘u’ = unified atomic mass unit & 1/12 th mass of single carbon-12 atom 

‘u’ = 1.66 x 10-24 g

(Just for understanding - Atomic mass approximately equal to twice of atomic no.)

Molecular mass of a substance is the sum of atomic masses of all the atoms in a molecule of a subitance.

Unit of molecular mass = 'u’

Molecular mass of H2 = 2 x 1 = 2u (Atomic mass of H=1)

Molecular mass of O2 = 16 x 2 = 32 u (Atomic mass of O=16)

Molecular Mass of Cl2 = 35.2 x 2 = 71 u (Atomic mass of Cl = 35.5)

Molecular Mass of CO2 = 12 x 1 + 16 x 2

                = 12 + 32 = 44 u ( Atomic Mass of C = 12)

Molecular Mass of CH4 = 12 x 1 + 4 x 1

               = 12 + 4 = 16 u

Molecular Mass of C2H6 = 12 x 2 + 6 x 1

               = 24 + 6 = 30 u 

Molecular Mass of C2H4 = 12 x 2 + 4 x 1

               = 24 + 4 = 28 u

Molecular Mass of  NH3 = 14 X 1 + 3 x 1

               = 14 x 3 = 17 u  (Atomic Mass of N = 14)

Molecular Mass of CH3OH = 12 x 1 + 4 x 1 + 16 x 1

               = 12 + 4 + 16 = 32 u


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Welcome to the NCERT Solutions for Class 9 Science - Chapter . This page offers a step-by-step solution to the specific question from Excercise 4 , Question 1: Calculate the molecular masses of H2, O2, Cl2, CO2, CH4, C2H6, C2H4, NH3, CH3OH.....