Question

The % composition of a compound is as follows : p = 43.7% & O = 56.3%. The molecular
weight of the compound is 142. Determine its Empirical and molecular formula



CLASS XI

Answer 1

Answer:

Empirical Formula  : P2O5  (Phosphorus Pentoxide)

Molecular Formula  : P2O5 (Phosphorus Pentoxide)

Explanation:

Assume 100 g of substance

p = 43.7%  , O = 56.3%

Molecular  weight of the compound  = 142.    

Empirical Formula  :  

Now convert the grams of each element to moles by dividing by their molar mass:                  

Moles of  P = (43.7)/30.9 = 2 moles  

Moles of  O =  56.3/16 = 4 moles    

Now ,Divide each of the mole  by the lowest of the two in order to simplify the mole ratio.    

2/2=1 mole  P    

4/2= 2 moles O      

Divide by fractional component of each mole value and round to closest whole numbers : O=5, P=2                      

 The resulting SIMPLEST WHOLE NUMBER empirical formula: P2O5

Molecular Formula = n= molecular mass /empirical formula mass

Molecular Formula : P2O5