Significance of the Mole


 
 
Concept Explanation
 

Significance of the Mole

Significance of Mole:

Mole is a SI unit of measurement for amount of substance (matter) since 1971. One mole of atoms or a compound means Avogadro number of atoms or molecules respectively.  Avogadro number is N = 6.022 X 10^2^3.

  • 1 Mole of a substance means M grams of that substance, where M is the Molar mass.  For example: For H_2 gas it is Molar mass = 2u. For NaOH, Molar mass= 40u.
  • Mole concept allows us to treat atoms and molecules (compounds) in a similar fashion. 1 mole of any ideal gas occupies 22.418 Liters of volume at STP conditions.
  •   Illustration: Calculate the volume at STP occupied by (i) 14g of Nitrogen

    Solution: Molecular mass of nitrogen = 28u

                      1 mole of nitrogen 22.4L at  STP i.e. 28g of nitrogen occupy = 22.4 liters at STP 

                      therefore 14g of nitrogen occupy = therefore frac{22.4}{28}times14 = 11.2L :at :STP

    Illustration: Calculate the volume at STP occupied by 10 ^{21} molecules of oxygen

    Solution:   1 mole of O_2 molecule = 6.022times10^2^3: molecules = 22.4 L: at: STP

                              10 ^{21} molecules of oxygen will occupy 

                              = frac{22.4}{6.022times10^{23}}times10^{21}L ;at: STP

                              = 3.72times10^{-2}L: at: STP

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    Sample Questions
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    Question : 1

    Find the number of moles of 48 g of oxygen gas ?

    Right Option : B
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    Explanation
    Question : 2

    1 Mole of a substance means M grams of that substance, where M is the ________________________.

    Right Option : D
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    Explanation
    Question : 3

    Find the mass of 1 mole of nitrogen atom ?

    Right Option : B
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    Explanation
     
     


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