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  1. define mole
  2. how is it related to avogadro constant , relative mass and molecular mass
  3. what is the no. of molecules in 0.25 moles of oxygen . avogadro's no =6.022*10 power is 23

1.  Mole is defined as any substance that contains elementary entities (atoms, molecules, ions) as there are atoms in 12 grams of pure carbon-12 (isotope of carbon with atomic weight 12). This equals to Avagadro’s constant equal to value .

 

2. The size of atoms and molecules are very tiny (sub-microscopic particles) and their number would be incredibly large even in a very small amount of a substance. To avoid these incredibly large numbers scientist have bought the concept of “mole”. Mole is used as unit. One mole of any kind of particle is  (it is a super large number).

 

For example 1 mole of gold =  of gold atoms

  1 mole of sugar =  of sugar

  similarly  1 mole of water =  of water

  A mole of molecule =  molecules

 

 is called the Avagadro’s number.

 

Mass of 1 mole of a substance in grams is equal to the substance molecular mass. So 1mole of water is 18.0 grams (molecular mass).

3. The no. of molecules in 0.25 moles of oxygen is 0.25 x  = 1.50 x 10^23 molecules.

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Mole is the SI unit of amount of substance. It is used for the measurement of very small, microscopic particles such as atoms and molecules. Broadly speaking, it is used to measure the number of particles – whether atoms or molecules present in a given amount of substance. One mole is the amount of substance that contains as many particles as there are atoms present in exactly 12g of 12C isotope off Carbon. It has been found that there are 6.023 X 1023 atoms present in 12 g of 12C isotope of Carbon.

  1. One mole of any substance will always contain 6.023 X 1023 particles, no matter what the substance is. Therefore 1 mole of Na atoms contains 6.023 X 1023 atoms of Na, 1 mole of Hydrogen atom contains 6.023 X 1023 atoms of Hydrogen atom, 1 mole of Hydrogen molecule will contain 6.023 X 1023 molecules of Hydrogen molecule (H2), 1 mole of CO2 will contain 6.023 X 1023 molecules of H2O.
  2. One mole of any substance is always equal to its molar mass in grams. We know that the molar mass of a substance in grams is always equal to the atomic mass (for atoms) or molecular mass (for molecules).
    Therefore 1 mole of Na atoms = molar mass of Na atoms = 23 g.
    1 mole of H2O molecules = molar mass of H2O molecules = 18.02 g
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According to Avogadro,

1 mole = 6.022*1023

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