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CBSE Class 9 Science Question 17 of 18

Atoms and Molecules — Question 1

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Question

Question 1

Calculate the molecular masses of

  1. H2
  2. O2
  3. Cl2
  4. CO2
  5. CH4
  6. C2H6
  7. C2H4
  8. NH3
  9. CH3OH.
Answer

  1. The molecular mass of H2 = 2 x atoms atomic mass of H = 2 x 1u = 2u

  2. The molecular mass of O2 = 2 x atoms atomic mass of O = 2 x 16u = 32u

  3. The molecular mass of Cl2 = 2 x atoms atomic mass of Cl = 2 x 35.5u = 71u

  4. The molecular mass of CO2 = atomic mass of C + (2 x atomic mass of O) = 12 + (2 × 16)u = 12 + 32 = 44u

  5. The molecular mass of CH4 = atomic mass of C + (4 x atomic mass of H) = 12 + (4 x 1) = 16u

  6. The molecular mass of C2H6 = (2 x atomic mass of C) + (6 x atomic mass of H) = (2 x 12) + (6 x 1) = 24 + 6 = 30u

  7. The molecular mass of C2H4 = (2 x atomic mass of C) + (4 x atomic mass of H) = (2 x 12) + (4 x 1) = 24 + 4 = 28u

  8. The molecular mass of NH3 = atomic mass of N + (3 x atomic mass of H) = 14 + (3 x 1) = 17u

  9. The molecular mass of CH3OH = atomic mass of C + (3 x atomic mass of H) + atomic mass of O + atomic mass of H = [12 + (3 × 1) + 16 + 1] = (12 + 3 + 17) = 32u