chemistry

How to Calculate Molecular mass of a Compound

As mass of an element is the atomic mass similarly mass of molecule is called molecular mass of a compound.

What is Molecular mass ?

Molecular mass is defined as “ the sum of atomic masses of all the atoms present in the molecule “ .

To find the molecular mass of a compound ,we have to add up the atomic masses of all the atoms in the compound.

Molecular Mass Calculation:

Water (H2O)

For Example

Molecular mass of H2O

H2O

=2(atomic mass of H) + atomic mass of O

=2  (1)  +  16

=2 + 16
=18 amu

Molecular mass of NH3

Ammonia ( NH3)

NH3

=14 + 3 (1)

=14 +3
=17 amu


1. Calculate the molecular mass of glucose C6H12O6 which is also known as blood sugar.

Problem solving strategy

Multiply atomic mass of carbon, hydrogen and oxygen by their subscripts and add.

SOLUTION

Molecular mass of C6H12O6 = 6(12.00) + 12(I.008) + 6(16.00)

= 180.096 amu


2. Calculate the molecular mass of naphthalene C10H8 which is used in mothballs.

Problem solving strategy

Multiply atomic mass of carbon, hydrogen by their subscripts and add.

SOLUTION

Molecular mass of C10H8 = 10 (12 )+ 8 (1)

= 120 + 8

= 128 amu

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