Gram Atomic Mass


 
 
Concept Explanation
 

Gram Atomic Mass

Atomic Mass: According to Dalton’s, each element has a characteristic atomic mass. But determining the mass of an individual atom was a relatively difficult task due to its very small size. Hence, their relative atomic masses were determined using the laws of chemical combinations and the compounds formed. For this purpose, initially 1/16 of the mass of an atom of naturally occurring oxygen was taken as standard unit because of the following two reasons: 

  • Oxygen reacted with a large number of elements and formed compounds.
  • This unit gave masses of most of the elements as whole numbers.
  • However in 1961, carbon (C- 12 isotope) was chosen as standard reference for measuring atomic masses universally because C-12 isotope of Carbon is the most abundant.

    Gram atomic mass is the atomic weight on the periodic table of an element in grams. It is the mass of 1 mole  of an element in grams, which is its moalr mass.

    Examples of values expressed in Gram atomic mass :

  • A hydrogen-1 atom has a mass of 1.007 u (or Da or amu) and its gram atomic mass is 1.007 grams.
  • A carbon-12 atom is defined as having a mass of 12 u and its gram atomic mass is 12 grams.
  • Sodium  has atomic weight of 22.99 u, so it has a gram atomic mass of 22.99 grams.
  • Sample Questions
    (More Questions for each concept available in Login)
    Question : 1

    Which of the following are correct ?

    (a)  A carbon-12 atom is defined as having a mass of 12 u and its gram atomic mass is 12 grams.

    (b)  Sodium  has atomic weight of 22.99 u, so it has a gram atomic mass of 22.99 grams.

     

    Right Option : C
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    Question : 2

    Which of the following are correct :

    (a) Oxygen reacted with a large number of elements and formed compounds.

    (b)  A hydrogen-1 atom has a mass of 2 u (or Da or amu) and its gram atomic mass is 2 grams.

    (c)   A carbon-12 atom is defined as having a mass of 12 u and its gram atomic mass is 12 grams.

    (d)  Sodium  has atomic weight of 25 u, so it has a gram atomic mass of 25 grams.

         

    Right Option : B
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    Question : 3

    Which isotope of Carbon is chosen as standard reference for measuring atomic masses universally?

    Right Option : B
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    Explanation
     
     


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