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Chapter: 11th Chemistry : Basic Concepts of Chemistry and Chemical Calculations

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Determination of Empirical Formula from Elemental Analysis Data

Determination of Empirical Formula from Elemental Analysis Data

Determination of Empirical Formula from Elemental Analysis Data :

 

Step 1:  Since   the   composition   is expressed  in  percentage,  we can consider the total mass of the compound as 100 g and the percentage values of individual elements as mass in grams.

Step 2:  Divide the mass of each element by its atomic mass. This gives the relative number of moles of various elements in the compound.

Step 3:  Divide the value of relative number of moles obtained in the step 2 by the smallest number of them to get the simplest ratio.

Step 4:  (only if necessary) in case the simplest ratios obtained in the step 3 are not whole numbers then they may be converted into whole number by multiplying by a suitable smallest number.

 

Example:

 

1. An acid found in tamarinds on analysis shows the following percentage composition: 32 % Carbon; 4 % Hydrogen; 64 % Oxygen. Find the empirical formula of the compound.


The empirical formula is C2H3O3


2. An organic compound present in vinegar has 40 % carbon, 6.6 % hydrogen and 53.4 % oxygen. Find the empirical formula of the compound.


The empirical formula is CH2O

Molecular formula of a compound is a whole number multiple of the empirical formula. The whole number can be calculated from the molar mass of the compound using the following expression



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