The shorthand representation of a substance(molecule of an element or a compound) in terms of symbols of elements and subscript numbers is called chemical formula.E.g. NaCl , AgNO3 ,H2O , C6H12O6 , CH4 etc.
It is of two types :
1) Molecular formula
2) Empirical formula
1) Molecular formula :The shorthand representation of a molecule in terms of symbols and subscript numbers is called molecular formula. It tells us about the actual ratio of various atoms present in one molecule of a compound. It is used to describe covalent compounds. E.g. H2O , C6H12O6 , CH4 etc.
2) Empirical Formula:-The chemical formula which gives simple whole number ratio of various atoms present in a chemical compound is called empirical formula or stoichiometric formula. It used to describe ionic compounds or giant covalent compounds. Example:NaCl is the empirical formula of table salt.CH is the empirical formula of benzene.HO is the empirical formula of hydrogen peroxide. CH2O is the empirical formula of glucose etc.
DETERMINATION OF EMPIRICAL AND MOLECULAR FORMULA
I) Write the symbols of each element in a tabular column.
II) Find out percentage composition of each element in the compound.
III) Write atomic mass of each element .
IV) Calculate moles of each element.
V) Find out molar ratio.
VI) Write down simplest whole number ratio.
VII) Write down empirical formula.
VIII) Calculate Molecular mass = 2 × V.D( if not given)
IX) Determine molecular formula :
2) A compound contains 75% C and 25% H. The molecular mass of the compound is 16 g .Determine empirical and molecular formula of this compound.
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3) An organic compound having molar mass 26 g contains 92.33% C and 7.67% H. Determine empirical and molecular formula of this compound.
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4) An organic compound has molar mass 60 g. it contains 40% C and 6.67% H and 53.33% O. Determine empirical and molecular formula of this compound.
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