Class 9 Chemistry Atoms and Molecules Mole


The word mole was coined by Wilhelm Ostwald from a Latin word moles meaning heap or piles. One mole of molecule or ion refers to the quantity in number possessing a mass equal to its atomic or molecular mass in grams. Number of particles present in one mole of any substance is 6.022 X 1023. This value is called Avogadro number.

So we get 1 mole = 6.022 X 1023 in number.

Mass of one mole of a molecule or ion is equivalent to its relative atomic or molecular mass in grams.


Let us calculate the number of moles in 48g of He. we will find it out by following process

  • Atomic mass of He =4u
  • Molar mass of He = 4g
  • Therefore the number of moles (n) = given mass (m) / molar mass (M)

n = 48/4 =12

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