Relative Atomic Mass


 
 
Concept Explanation
 

Relative Atomic Mass

Relative Atomic Mass: It is defined as the number of times a given atom is heavier than 1/12th of mass of 1 atom of carbon-12 (C-12) or it is the average mass of the atom as compared to 1/12th the mass of one carbon-12 atom.

The relative atomic mass, of an element is calculated from:

  • the mass number of its isotopes.
  • the abundance  of these isotopes.
  • Chlorine : 

    Chlorine natuarlly exists as two isotopes,_{17}^{35}Cl and _{17}^{37}Cl. The abundance of chlorine -35 is 75% and the abundance of chlorine-37 is 25%.

    To calculate relative atomic mass, A_r, of chlorine:

    A_r=frac{total:mass :of :atoms }{total: number :of: atoms}=frac{(35times75)+(37times25)}{75+25}

    A_r=frac{2625times925}{100}=frac{3550}{100}

    A_r=35.5

    Sample Questions
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    Question : 1

    What is the relative atomic mass of Chlorine ?

    Right Option : B
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    Question : 2

    Calculate the relative atomic mass of Chlorine . If it have two isotopes having atomic mass 35 and 37, The abundance of chlorine -35 is 75% and the abundance of chlorine-37 is 25%.

    Right Option : A
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    Question : 3

    Which of the following are correct :

    (a) Relative Atomic Mass is defined as the number of times a given atom is heavier than 1/12th of mass of 1 atom of carbon-12.

    (b) Relative Atomic Mass is the average mass of the atom as compared to 1/12th the mass of one carbon-12 atom.

    Right Option : C
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    Explanation
     
     


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