Mole Concept Basics - Definition, Formula, Examples, FAQs

Edited By Team Careers360 | Updated on Sep 19, 2024 07:33 PM IST

Quite commonly, we use different units for counting such as dozen for 12 articles, score for 20 articles, and gross for 144 articles, irrespective of their nature. For example, one dozen means 12 books whereas, one dozen apples means 12 apples. Similarly, chemists use the unit for counting atoms, molecules, ions, etc. A mole is a collection of 6.022*10²³ particles. The mass of one mol of a substance is called its molar mass (M).

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This Story also Contains

What is a Mole?
Relationship of Mole
To Find the Total Number of Identities
Some Solved Examples
Conclusion

Mole Concept Basics - Definition, Formula, Examples, FAQs

What is a Mole?

A mole is a unit that represents 6.023 x 10²³ particles, atoms, molecules ions, etc., irrespective of their nature.
Mole is related to the mass of the substance, the volume of the gaseous substance, and the number of particles
Mole $=\frac{W}{M}=\frac{(\text { Wt. of substance in gm. })}{(\text { Molar mass of substance (G.m.m) }}$

Here G.m.m. = Gram molecular mass or molar mass which is the mass of 1 mole of any substance

Mole $=\frac{\text { (Volume of substance in litre })}{22.4 \text { litre }}$
The volume of one mole of any gas is equal to 22.4 liters or dm³ at STP. It is known as molar volume.
Mole $=\frac{\text { Number of identities }}{\text { Avogadro's number }}$

Relationship of Mole

A mole of any substance (like O₂) stands for:

6.023 x 10²³molecules of O₂
2 x 6.023 x 10²³ atoms of Oxygen
32 gm of Oxygen
22.4 litre of O₂ at STP.

To Find the Total Number of Identities

Total number of Molecule = mole(n) x N_A
Total number of Atoms = mole (n) x N_A x No. of atoms present in one molecule (atomicity).
Total number of Electrons = mole (n) x N_A x No. of electrons present in one atom.
The total charge on any ion = mole (n) x N_A x charge on one ion x 1.6 x 10^-19 C

Some Solved Examples

Qu 1: Number of atoms in 558.5 gram Fe (at. wt. of Fe = 55.85 g mol^-1) is:

1) twice that in 60 g carbon

2) 6.023 × 10²²

3) half that in 8 g He

4) 558.5 × 6.023 × 10²³

Solution

Number of moles of Fe atom $=\frac{558.5}{55.85}=10 \mathrm{Mole}$

Total number of atom

$\begin{aligned} & =10 \times 6.022 \times 10^{23}=6.022 \times 10^{24} \\ & =10 \times N_A\end{aligned}$

12 g of carbon means Avogadro's number,

therefore, 60 g of carbon means, 5 moles of carbon and thus contains 5×N_A atoms, twice of this equals 10N_A atoms of carbon.

Hence, the answer is the option (1).

Qu 2: If we consider that 1/6, in place of 1/12, the mass of the carbon atom is taken to be the relative atomic mass unit, the mass of one mole of a substance will

1) decrease twice

2) increase two-fold

3) remain unchanged

4) be a function of the molecular mass of the substance.

Solution

When you consider 1/6 in place of 1/12 since the mass of the carbon atom is still the same, new amu1 = 2amu ( where amu1 is the new amu unit and amu is the old amu unit). So now Na1 (Avogadro's number) becomes half ( Na/2) since the weight of carbon corresponding to atomic weight becomes 6gm in place of 12. ( where Na1 is the new Avogadro's number and Na is the old Avogadro's number). And we know that the mass of one mole of a substance is = Na x amu. So new atomic mass= Na1 x amu1 = Na/2 x 2amu = Na x amu = old atomic weight.

Hence, the answer is the option (3).

Qu 3: What is the total number of moles if we have a mixture of 34g of Ammonia, 78g of Benzene, and 10g of Hydrogen?

1) 8

2) 9

3) 7

4) 10

Solution

Number of moles of ammonia $=\frac{\text { mass of ammonia }}{\text { molar mass of ammonia }}=\frac{34}{17}=2$

Number of moles of benzene $=\frac{78}{78}=1$

Number of moles of hydrogen $=\frac{10}{2}=5$

Total number of moles = 2 + 1 + 5 = 8

Hence, the answer is (8).

Qu 4: We have a substance x. What is the molar mass (in g) of x if 2 moles of it weigh 196g?

1) 147

2) 196

3) 98

4) 49

Solution

Molar mass of $x=\frac{196}{2} g=98 g$

Hence, the answer is (98g).

Qu 5. 14 g of Nitrogen gas and 22 g of CO₂ gas are mixed together. Find the volume of the gaseous mixture at STP.

(Response should be up to only one decimal digit like 78.7).

1) 22.4

2) 11.2

3) 44.8

4) 52.8

Solution

Number of Moles of a gas at STP -

no. of moles of a gas at STP = given volume of gas / 22.4 liter

Moles of N₂=0.5

moles of CO₂=0.5

So total moles 0.5+0.5=1

So vol. at STP $=1 \times 22.4=22.4 \mathrm{lit}$

Hence, the answer is the option (1).

Conclusion

The number 6.022 x 10²³ is called the Avogadro number or Avogadro constant. It is denoted by N_A in honor of nineteenth-century Italian scientist, Amedeo Avogadro. In other words, a mole is an Avogadro number of particles. It may be noted that the mole concept is also applicable to ionic compounds which do not contain molecules. The mass of one mole of any substance will be its molar mass and it contains 6.022 x 10²³ particles of that substance.

Also check-

NCERT Chemistry Notes:

Frequently Asked Questions (FAQs)

1. What is the significance or what Mole concept Basics?

In chemistry, moles define everything. The Mole concept Basics is the subject of most quantitative chemical calculations, so understanding the Mole concept Basics is important in chemistry. An understanding of how mass, number of entities, and moles relate.

2. How does chemistry work with moles?

An atom or molecule is a very small object, such as an atom, a molecule, or some other object. In chemistry, the Mole concept Basics is used to calculate the amount of such a small object.

3. What is the purpose of mole unit fraction?

A mole unit fraction is defined as the number of single component molecules (or moles) divided by the total number of molecules (or moles) in the mixture. If two reactive components are mixed, a mole fraction is useful since the ratio of the two components can be understood if a mole fraction is known for each component.

4. What does mole fraction mean in terms of partial pressure?

A mixture's partial pressure depends on the relative mole fraction of each gas. It is independent of the pressure exerted by any other gas present in the mixture that each gas exerts (its partial pressure).