How to calculate molecular mass

Molecular mass is the sum of atomic masses of the elements present in a molecule. It is obtained by multiplying the atomic mass of each element by the number of its atoms and adding them together. For e.g. molecular mass of H2SO4 is calculated as: 2 x 1 + 32 + 4 x 16 = 98 u.

In the case of ionic compounds (like NaCl), there is no discrete (separate) molecules. Here the positive ions and the negative ions are arranged in a three-dimensional structure. So we can calculate only formula mass by taking molecular formula of the compound.

Calculating Molecular Mass:-

The molecular mass of a substance is calculated by adding up the atomic masses of all the atoms in the molecule. The atomic mass of an element is the mass of a single atom of that element, expressed in amu.

For example, the molecular mass of water (H2O) can be calculated as follows:

Molecular mass of water (H2O) = (2 x atomic mass of hydrogen) + (1 x atomic mass of oxygen) = (2 x 1.008 amu) + (1 x 16 amu) = 18 amu

This means that one molecule of water has a molecular mass of 18 amu.

Molecular mass is not the same as molar mass: Although the terms “molecular mass” and “molar mass” are often used interchangeably, they actually refer to slightly different concepts. Molecular mass is the mass of a single molecule, while molar mass is the mass of one mole of a substance. However, since one mole of a substance contains Avogadro’s number of molecules, the two concepts are related: the molar mass of a substance is equal to its molecular mass multiplied by Avogadro’s number.

Molecular mass of Simple Covalent Compound

Q.What is the molecular mass of water?
A)18
B)32
C)16

Water (H2O):- 2 + 16 = 18 u

Q.What is the molecular mass of Methane?
A) 16
B) 17
C) 18

Q.What is the molecular mass of Ammonia?
A) 14
B) 15
C) 17

Q.What is the molecular mass of Carbondioxide?
A) 40
B) 41
C) 44

Q.What is the molecular mass of HCl ?
A) 36
B) 35
C) 35.5

Q.What is the molecular mass of Ozone?
A) 16
B) 32
C) 48

Q.What is the molecular mass of Dinitrogen?
A) 28
B) 14
C) 30

Q.What is the molecular mass of Nitrogen dioxide?
A) 44
B) 45
C) 46

Q.What is the molecular mass of Sulphur molecule?
A) 250
B) 260
C) 256

Q. Molecular mass of Benzene?
A) 78
B) 76
C) 72

Q. Molecular mass of Sulphuric acid?
A) 98
B) 96
C) 94

Q. Molecular mass of Carbon Monoxide?
A)
B)
C)

Q. Molecular mass of Nitrogen Monoxide?
A)
B)
C)

Q. Molecular mass of Dioxygen?
A)
B)
C)

Q. Molecular mass of Phosphorus molecule?
A)
B)
C)

Q. Molecular mass of Sulphur Trioxide?
A)
B)
C)

Q. Molecular mass of Sulphur Dioxide?
A)
B)
C)

Q. Molecular mass of ?
A)
B)
C)

1.Water (H2O):- 2 + 16 = 18 u

2. Ammonia (NH3) :- 14 + 3 = 17 u

3. Methane (CH4) :- 12 + 4 = 16 u

4. Carbon Dioxide ( CO2) :- 12 + 32 = 44 u

5. Carbon Monoxide ( CO ) :- 12 + 16 = 28 u

6. Ozone (O3) :- 48u

7. Dinitrogen ( N2) :- 14 + 14 = 28u

8. Dioxygen ( O2) :- 16 + 16 = 32

9. Hydrochloric acid (HCl) :- 1 + 35.5 = 36.5 u

10. Nitrogen Dioxide ( NO2) :- 14 + 32 = 46 u

11. Nitrogen Monoxide (NO) :- 14 + 16 = 30 u

12. Phosphorus molecule (P4) :- 4 x 31 = 124 u

13. Sulphur molecule (S8) :- 8 x 32 = 256 u

14. Sulphur Dioxide (SO2) :- 64 u

15. Sulphur Trioxide (SO3) :- 80 u

Molecular Mass Quiz -1

16. Ethane ( C2H6) :- 24 + 6 = 30 u

17. Butane ( C4 H10) :- 48 + 10 = 58 u

18. Dihydrogen(H2):- 1+1 = 2 u

19 Chlorine gas (Cl2) :- 2 x 35.5 = 71 u

20. Argon gas (Ar):- 40

  • -Molecular mass (or molecular weight) is the mass of a single molecule of a substance. It is calculated by adding up the atomic masses of all the atoms in the molecule.
  • -Molar mass, on the other hand, is the mass of one mole of a substance. It is expressed in units of grams per mole (g/mol) and is numerically equal to the molecular mass in atomic mass units.

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