# Molecular Weight Formula – Definition, Formula, Solved Examples

Last Updated : 19 Dec, 2023

An atom is the basic building block of matter i.e. everything around us is made of matter. This is the smallest unit into which matter can be divided without the release of any electrically charged particles. This is the smallest unit of matter which has the characteristic properties of a chemical element. The mass of an atom depends on the electrons and neutrons present in the atoms. A number of atoms combine together to form a molecule.

Molecules are made up of one or more than one atoms. The mass of a molecule depends on the different atoms present in the molecule. The mass of the molecule is known as the molecular mass. It is measured in Daltons. It is even referred to as molecular mass, molecular weight, or molar mass. Dalton is defined as the relative to the mass carbon-12 isotope. An atomic mass unit is described as the weight of the carbon-12 isotope divided by 12. The molecular mass of a material is important to know the number of grams present in one mole of the given substance.

Molecular mass of some of the elements are:

Atomic No.                Name of  Element                  Mass No.
1 Hydrogen 1
2 Helium 4
3 Lithium 7
4 Beryllium 9
5 Boron 10
6 Carbon 12
7 Nitrogen 14
8 Oxygen 16
9 Florine 19
10 Neon 20
11 Sodium 23
12 Magnesium 24
13 Aluminum 27
14 Silicon 28
15 Phosphorous 31
16 Sulfur 32
17 Chlorine 35.5
18 Potassium 39
19 Argon 40
20 Calcium 40

The molecular mass of a molecule is equal to the sum of the mass of each atom present in the molecule.

Molecular mass of compound = {(number of atoms in a compound)Ã—atomic mass} for each atom.

## Problems based on Molecular Mass

Problem 1: What is the molecular mass of Ethene?

Solution:

The molecular formula of ethene is C2H4

The atomic mass of carbon is 12 and the atomic mass of hydrogen is 1

So the molecular mass is (2Ã—12) + (4Ã—1)

= 24 + 4

= 28

Problem 2: What is the molecular mass of Methanol?

Solution:

The molecular formula of Methanol is CH3OH

The atomic mass of carbon is 12, the atomic mass of hydrogen is 1 and the atomic mass of oxygen is 16

So the molecular mass is (1Ã—12) + (4Ã—1) + (1Ã— 16)

=12 + 4 + 16

=3

Problem 3: What is the molecular mass of Propane?

Solution:

The molecular formula of Propane is C3H8

The atomic mass of carbon is 12 and the atomic mass of hydrogen is 1

So the molecular mass is (3Ã—12) + (8Ã—1)

= 36 + 8

= 44

Problem 4: What is the molecular mass of Heptane?

Solution:

The molecular formula of Heptane is C7H16

The atomic mass of carbon is 12 and the atomic mass of hydrogen is 1

So the molecular mass is (7Ã—12) + (16Ã—1)

= 84 + 16

=100

Problem 5: What is the molecular mass of Ethane?

Solution:

The molecular formula of Ethane is C2H6

The atomic mass of carbon is 12 and the atomic mass of hydrogen is 1

So the molecular mass is (2Ã—12) + (6Ã—1)

= 24 + 6

= 30

Problem 6: What is the molecular mass of Butanol?

Solution:

The molecular formula of Butanol is C4H8O

The atomic mass of carbon is 12, the atomic mass of hydrogen is 1 and the mass of oxygen is 16

So the molecular mass is (4Ã—12) + (8Ã—1) + (1Ã—16)

= 48 + 8 + 16

= 72

Problem 7: What is the molecular mass of Benzoic acid?

Solution:

The molecular formula of Benzoic acid is C6H5COOH

The atomic mass of carbon is 12, the atomic mass of hydrogen is 1 and the atomic mass of oxygen is 16

So the molecular mass is (6Ã—12) + (6Ã—1) + (2Ã—16)

= 72 + 6 + 32

=110

Problem 8: What is the molecular mass of Styrene?

Solution:

The molecular formula of Methanol is C8H8

The atomic mass of carbon is 12 and the atomic mass of hydrogen is 1

So the molecular mass is (8Ã—12) + (1Ã—8

= 84 + 8

= 92

Problem 9: What is the molecular mass of Valine?

Solution:

The molecular formula of Valine is C5H11NO2

The atomic mass of carbon is 12 ,the atomic mass of hydrogen is 1, the atomic mass of oxygen and atomic mass of nitrogen is 14

So the molecular mass is (5Ã—12) + (1Ã—11) + (1Ã—14) + (2Ã— 16)

= 60 + 11 + 14 + 32

=117

Question: Define a molecule.

A number of atoms combine together to form a molecule. Molecules are made up of one or more than one atoms. The mass of a molecule depends on the different atoms present in the molecule. The mass of the molecule is known as the molecular mass.

Question: What is Molecule mass?

The mass of the molecule is known as the molecular mass. It is measured in Daltons. It is even referred to as molecular mass, molecular weight, or molar mass. Dalton is defined as the relative to the mass carbon-12 isotope. An atomic mass unit is described as the weight of the carbon-12 isotope divided by 12. The molecular mass of a material is important to know the number of grams present in one mole of the given substance.

Question: What are Molecular formulas and Empirical formulas?