JEE Main & Advanced Chemistry Chemical Arithmetic Percentage composition & Molecular formula

Percentage composition & Molecular formula

Category : JEE Main & Advanced

Percentage composition & Molecular formula

         (1) Percentage composition of a compound

Percentage composition of the compound is the relative mass of each of the constituent element in 100 parts of it. If the molecular mass of a compound is M and B is the mass of an element in the molecule, then

           \[\text{Percentage of element }=\frac{\text{Mass of element }}{\text{Molecular mass}}\times 100=\frac{X}{M}\times 100\]

         (2) Determination of empirical formula : The empirical formula of a molecule is determined using the % of elements present in it. Following method is adopted.

Element

% Relative no. of atoms = %/at. wt.

Simplest Ratio

Empirical Formula

           Relative no. of atoms : Divide the percentage of each element present in compound by its at. weight. This gives the relative no. of atoms of element in molecule.

           Simplest ratio : Find out lowest value of relative no. of atoms and divide each value of relative no. of atoms by this value to estimate simplest ratio of elements.

           It the simplest ratio obtained are not complete integers, multiply them by a common factor to get integer values of simplest ratio.

           Empirical formula : Write all constituent atoms with their respective no. of atoms derived in simplest ratio. This gives empirical formula of compound.

           Molecular formula : Molecular formula \[=n\times \]empirical formula where \['n'\] is the whole no. obtained by

                \[n=\frac{\text{molecular weight of compound}}{\text{empirical formula weight of compound}}\]



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