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Molecular Weight Formula

Molecular weight is nothing but the weight of atoms in a molecule. Each element has its own mass but distinct weight that depends on number of atoms present in it. Hence molecular weight is the sum of mass of the constituent atom multiplied by the number of atoms present in the element. 
Molecular weight formula is given by
Molecular Weight Formula

 

Molecular Weight Examples

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Lets see some examples on molecular weight:

Solved Examples

Question 1: What is the molecular weight of Fe2o3?
Solution:
 
Fe2O3 contains two atoms of iron and three atoms of oxygen
Mass of Fe = 55.847 amu,
Mass of O = 15.9994 amu

Molecular weight of Fe2O3 is
= 2 $\times$ 55.847 amu + 3 $\times$ 15.9994 amu
= 159.692 amu.
 
 

Question 2: what is the molecular weight of K2 so4?
Solution:
 
K2so4 contains two atoms of potassium, one atom of sulphur and four atoms of oxygen
Molecular mass of K = 39.098 amu,
Molecular mass of s = 32.066 amu,
Molecular mass of o = 16.999 amu

Molecular weight of K2so4 is
= 2 $\times$ 39.098 amu + 1 $\times$ 32.066 amu + 4 $\times$ 16.999 amu
= 174.298 amu
 
 

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