Mass of 1 Mole of atom is called Molar Mass
How is Molar Mass Calculated?
The molar mass of a substance is equal to the atomic mass of a substance taken in grams .
Molar mass is the mass of 1 mole of a substance .
It is denoted by the letter M .
Let us calculate the Molar Mass of Calcium Carbonate (CaCO 3 )
What is a Molecule?
A group of atoms chemically bonded together is Here are the valency of a few elements:
called Molecule
1 molecule of CaCO 3 consists of : 1 Calcium (Ca) atom
1 Carbon (C ) atom
3 Oxygen (O) atoms
M of CaCO 3 = (1 x mass of Ca) + (1 x mass of C) + (3 x mass of O)
M of CaCO 3 = (1 x 40) + (1 x 12) + (3 x 16)
M of CaCO 3 = (1 x 40) + (1 x 12) + (3 x 16)
M of CaCO 3 = 100g/mol
Example 1
Atomic Mass of hydrogen = 1 u
Hence, Gram Atomic Mass = 1 gram
It means that Mass of 1 mole of Hydrogen = 1 gram
Since 1 MOLE = 6.022 x 10 23 atoms
We can say that
Mass of 6.022 x 10 23 atoms of Hydrogen = 1 gram/mole
What is a Molecule?
A group of atoms chemically bonded together is Here are the valency of a few elements:
called Molecule
Example 2
Atomic Mass of oxygen atom = 16 u
Hence, Gram Atomic Mass = 16 gram
It means that Mass of 1 mole of Oxygen = 16 grams
Since 1 MOLE = 6.022 x 10 23 atoms
We can say that
Mass of 6.022 x 10 23 atoms of Oxygen = 16 grams/mole
Some formulae related to mole
1 mole of an atom = 6.022 x 10 23 atoms = molar mass of that atom
That is,
1 mole of C (Carbon) = 6.022 x 10 23 atoms of C (Carbon) = 12g of Carbon
What is a Molecule?
A group of atoms chemically bonded together is Here are the valency of a few elements:
called Molecule
Sometimes we're given the values of 2 things and are supposed to find the value of the third.
So, we should remember that,
FORMULA 1 - Number of moles of a substance = Given mass of the substance / Molar mass of the substance
= m/M
Q Find number of moles of H 2 in 10g of H 2
Ans Given mass of H 2 = m =10g
Molar Mass of H 2 = M= 2g/mol
We know that,
Number of moles of a substance = Given mass of the substance / Molar mass of the substance
= m/M
= 10g / 2g mol -1
= 5 moles
What is a Molecule?
A group of atoms chemically bonded together is Here are the valency of a few elements:
called Molecule
- How many moles are there in 52g of Helium?
We know that
Atomic Mass of Helium = 4 u
So Molar Mass of Helium = 4 g mol -1
It means that Mass of 1 mole of Helium = 4 grams
We can also write as
= m/M
= 52/4
=13
So, 13 moles are there in 52g of Helium
FORMULA 2 - Number of moles of a substance = Number of particles of the substance / Avogadro's Constant
= Number of particles / 6.022 x 10 23
= N/N O
- How many moles is 12.044 x 10 23 atoms of He?
A Number of atoms of the He = N = 12.044 x 10 23
What is a Molecule?
A group of atoms chemically bonded together is Here are the valency of a few elements:
called Molecule
Avogadro's Constant = N O = 6.022 x 10 23
We know that,
Number of moles of a substance = Number of particles of the substance / Avogadro's Constant
= N/N O
= 11.044 x 10 23 / 6.022 x 10 23
= 2 moles of He atoms
Note - We usually denote number of moles by 'n'
So, this brings us to the 3rd formula;
FORMULA 3 - Given mass of the substance / Molar mass of the substance = Number of particles of the substance / Avogadro's Constant
=> m/M = N/N O
Example - 3.3, 3.4
In text Question -
NCERT Question -7,8,9,10,11
What is a Molecule?
A group of atoms chemically bonded together is Here are the valency of a few elements:
called Molecule
