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:

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

NH₃

=14 + 3 (1)

=14 +3
=17 amu

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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

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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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