# What is Atomic Mass in Chemistry ?

Updated on Jan. 8, 2021 03:19 PM IST by Lakshmi Arya

#### Atomic Mass:-

1. The mass of an atom of an element is called it's atomic mass.
2. In 1961, IUPAC have accepted atomic Mass Unit (u) to express atomic and molecular mass of elements and compounds.

#### Molecular Mass:-

1. It is the sum of atomic masses of all the atoms present in a molecule of that substance.
2. Example: molecular mass of H2O=2×atomic mass of Hydrogen+1×atomic mass of oxygen. So, Molecular mass of H2O=2×1+1×16=18u

Calculate the molecular masses of NaCl, CuSO4, HNO3.

1. Molecular mass of NaCl=1×atomic mass of sodium+1×atomic mass of chlorine So, molecular mass of NaCl=1×23+1×35.5=58.5u
2. Molecular mass of CuSO4=1×atomic mass of copper+1×atomic mass of sulphur+4×atomic mass of oxygen So, molecular mass of   CuSO4=1×63+1×32+4×16=159u
3. Molecular mass of HNO3=1×atomic mass of Hydrogen+1×atomic mass of nitrogen+3×atomic mass of Oxygen So, molecular mass of HNO3=1×1+1×14+3×16=63u

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