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RELATIVE ATOMIC MASS,MOLECULAR MASS and FORMULA MASS

RELATIVE ATOMIC MASS
Relative atomic mass is the mass of an atom of an element as compared to the mass of an atom of carbon taken as 12.
Relative atomic masses are measured in atomic mass units (amu).
1 a.m.u. is 1/12th part of mass of an atom of C-12.
1 a.m.u.= 1.661×10-27kg
               = 1.661×10-24g
For example: Hydrogen and oxygen have relative atomic masses 1.008 amu and 15.9994 amu respectively.
MOLECULAR MASS 
The sum of the relative atomic masses of all the elements present in the molecule of a compound is called molecular mass.  Example: H2O = 18 a.m.u., CO2 = 44 a.m.u.
FORMULA MAS 
The sum of the relative atomic masses of all the elements present in the formula unit of the compound is called formula mass Example: NaCl =58.5 a.m.u.,CaCO3 = 100 a.m.u.

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