Comparing MOLE OR AVOGADRO'S NUMBER

MOLE 

1. The relative atomic mass of an element, the relative molecular mass of a molecule, the relative formula mass of an ionic substance or ionic mass of ionic specie when expressed in grams is called gram mole or simply mole.
2. One mole of a substance is the amount in grams which contains 6.02×1023 particles of that substance.

• It is denoted by “n”.
• It is abbreviated as “mol”.
• It is the  basic SI unit of measuring the quantity of substance.

Example:

(i)  Element                                Na       =          23g      = 1mole

(ii) Molecular compound        H2O     =          18g      = 1mole

(iii) Ionic compound               NaCl      =          58.5g   = 1mole

(iv) Ionic specie                       HCO-3    =          61g      = 1mole

(i) Gram atom (mole):

The relative atomic mass of an element when expressed in grams is called gram atom it is also called 1mole.

Example:

1gram atom (1mole) of Na = 23g

1gram atom (1mole) of Cl = 35.5g

Number of gram atoms or moles of an element =

(ii) Gram molecule (mole):

The relative molecular mass of a molecule when expressed in grams is called gram molecule. It is also called 1mole.

Example:

1gram molecule (1mole) of water = 18 g of H2O

1gram molecule (1mole) of sulphuric acid = 98 g of H2SO4

(iii) Gram formula (mole):

The relative formula mass of a formula unit when expressed in grams, is called gram formula. It is also called 1mole.

Example:

1gram formula (1mole) of NaCl     = 58.5 g

1gram formula (1mole) of Na2CO3 = 106 g

(iv) Gram ion (mole):

The ionic mass of an ionic specie when expressed in grams, is called gram ion or one mole of ion. It is also called 1mole.

Example:

1gram ion (1mole) of OH-  = 17g

1gram ion (1mole) of SO42–= 96 g

Number of gram ions or moles of an ionic specie = 

AVOGADRO'S NUMBER 

The number of particles (atoms, ions, molecules, formula units) present in one mole of the respective substance is called Avogadro’s number or Avogadro’s constant.

• It is denoted by NA.
•  Its value is 6.022 × 1023

Example:

Na   = 23g      = 1mole = 6.022 ×1023atoms.

H2O   = 18g    = 1mole = 6.022 × 1023Molecules.

NaCl  = 58.5g = 1mole = 6.022 × 1023formula units.

CO32– = 60g   = 1mole = 6.022 × 1023ions.

Number of atoms of an element     

Number of molecules of compound   = × NA

Number of formula units of ionic compounds   = x NA.

Number of ions = × NA. 

MOLAR VOLUME 

The volume occupied by one mole of an ideal gas at standard temperature (0°C or 273K) and pressure (1 atm), (STP) is called molar volume.

• Its value is 22.414dm3 22414 cm3.
• It is only applicable for ideal gasses at STP.  

Example:

2.016g of H2 = 1mole of H2=6.022x1023 molecules of H2 = 22.414dm3 volume of H2 at S.T.P.

16g of CH4 = 1mole of CH4=6.022x1023 molecules of CH4 = 22.414dm3 volume of CH4 at S.T.P.

It is very interesting to know from the above data that 22.414dm3 of each gas has a different mass but the same number of molecules.

Reason:

The reason is that the masses and the sizes of the molecules do not affect the volumes. Normally, it is known that in the gaseous state the distance between molecules is 300 times greater than their diameters.