Mole and Avogadro’s Number (N_A):

What is Mole?

In simple words, mole(n) is defined as the amount of substance that contains 6.022 x 10²³ particles ( atoms, molecules or ions)

Or:

A mole can also be defined as ” the atomic mass, molecular mass or formula mass expressed in grams is equal to 1 mole of a substance”.

(1)   A mole is a  counting unit which contains 6.022 x 10²³ particles

As!!

12 things = dozen

2 things = Pair

144 things = gross

1 Kg    =   1000 g

similarly:

  1 mole =  6.022 x 10²³ particles

“One mole of a substance contains Avogadro’s number (6.02 x 10²³) of things or particles”.

e.g. (i)  6.02 x 10²³ atoms of Hydrogen are called one mole or one gram-atom of Hydrogen.

e.g. (ii) 6.02 x 10²³ molecules of Hydrogen are called one mole or one gram-molecule of Hydrogen.

e.g. (iii) 6.02 x 10²³ electrons are called one mole of electrons.

Avogadro’s number (N_A) :

Avogadro’s number is defined as “the number of particles that are present in one mole of a substance “.

Avogadro’s number (N_A) value is 6.022 x 10²³ .

Its unit is mol^-1

How do you calculate moles in chemistry?

Formulae to calculate moles of a substance are as follows:

 Number of moles = Number of particles /   6.02 x 10²³

(2)        “Atomic mass in grams is also called a mole or gram atom.”

 Number of moles = Mass In grams / Atomic mass in grams or Molar mass

(3)        “Molecular mass in grams is also called a mole or gram molecule.”

 Number of moles =      Mass In grams / Molecular mass in grams or Molar mass

(4)        Volume of one mole of a gas at STP is 22.4 dm³ or litre.

No of moles = Volume (in dm³) at STP  / 22.4

(5)        Volume of one mole of a gas at RTP is 24 dm³ or litre.

Volume (in dm³) at RTP        

No of moles = Volume (in dm³) at RTP   / 24

Standard temperature = 0^oC or 32^oF or 273K               and      Standard pressure = 1atm or 760 mmHg(Torr) or 1.01×10⁵ N/m² (Pa) or 14.7 PSI(Ib/in²)

Room temperature = 25^oC or 77^oF or 298K                 and      Room pressure = 1atm or 760 mmHg(Torr) or 1.01×10⁵ N/m² (Pa) or 14.7 PSI(Ib/in²)

(6)        Moles of solute in the solution = MV                   

      where M = molarity of a solution

                  V = volume of solution indm³

• A molecular formula shows the number of atoms of different elements in a molecule of a compound, as well as shows number of moles of atoms of elements in a mole of a compound.

e.g. One molecule of Ethyl alcohol (C₂H₅OH) contains two atoms of Carbon, six atoms of Hydrogen and one atom of Oxygen.

                OR

One mole of Ethyl alcohol (C₂H₅OH) contains two moles of Carbon atoms, six moles of Hydrogen atoms and one mole of an Oxygen atom.

Related Important Questions !!

Q1.What is the mass of one mole Carbon atom?

Ans. The mass of one mole of carbon atom is 12g.

Q2.How many moles are there in 60g of NaCl?

Solution:

Given:

Mass of NaCl= 60g

Moles of NaCl = ?

SOLUTION:

Molar mass of NaCl= 23+35.5= 58.5g/mol

 FORMULA:

No of moles= mass / molar mass

No of moles= 60 / 58.5

No of moles(n) =1.02 mol

Q3.What is the mass of 0.5 moles of CaCO3?

SOLUTION:

Moles of CaCO3 = 0.5 mol

Mass of CaCO3 =?

SOLUTION:

Molar mass of CaCO3 = 100 g/ mol

 FORMULA:

No of moles= mass / molar mass

Mass of CaCO3 = moles. X   molar mass

Mass of CaCO3 =  0.5   X100

                       = 50g CaCO3

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