Note on Molecular Weight and Concept of Mole

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Atomic weight:

The sum total of the number of protons and neutrons present in the nucleus of an atom is called atomic weight.

Molecular weight: The sum total of the atomic weights of various atoms present in a substance is called molecular weight. For example:

Molecular weight of CaCO3 = ( 40 + 12 + 16×3)
= (40 + 12+ 48)
= 100

Similarly,
Molecular weight of water = H2O
= (1×2 + 16)
= 18

Gram Molecular weight:

The molecular weight of a substance which is expressed in terms of gram is called gram molecular weight. For example:

The gram molecular weight of CaCO3 is 100 gm.

Avogrado Number:

Each mole of any substance contains 6.023 x 1023 particles or ions or atoms or molecules and this number is called Avogrado number.

Mole:

The collection of 6.023 x 1023 particles or ions or atoms of a substance is called its one mole. Mole is equal to the gram molecular weight of a substance. For example:

Gram molecular weight of CaCO3 = 100 gm.
1 mole of CaCO3 = 100 gm.
100 gram of CaCO3 = 6.023 x 1023 particles

Rate of reaction:

It is defined as the change in concentration of any one of the reactants or products per unit time to complete the reaction.

Factors affecting rate of reaction:

  1. In general, increase in temperature increases the rate of almost all chemical reaction while decrease in temperature decreases the reaction rate.
  2. The rate of reaction increases with increase in the concentration of reactants.
  3. The rate of reaction also depends upon the nature of the atom.

  • The sum total of the number of protons and neutrons present in the nucleus of an atom is called atomic weight.
  • The sum total of the atomic weights of various atoms present in a substance is called molecular weight.
  • The molecular weight of a substance which is expressed in terms of gram is called gram molecular weight.
.

Very Short Questions

2KClO3 = 2KCl + 3O2 (Balanced chemical equation)
or, 2(39 + 35 + 3 × 16) = 2 (39 + 35) + 3(2 × 16)
or, 2 × 122 = 148 + 96
or, 244 = 148 + 96

244 gms of potassium chlorate on strongly heating gives 148 gms of potassium chloride and 96 gms of oxygen.
∵ 244 gms of KClO3 will yield 148 gms of KCl
1 gm of KClO3 will yield 148/244 gms of KCl
∴ 10 gms of KClO3 ­will yield (10 × 148) / 244 = 6.06 gms of KCl
∵ 244 gms of KClO3 will yield 96 gms of O2
1 gm of KClO3 will yield 96 / 244 gms of O2
∴ 10 gms of KClO3 will yield (10 × 96 ) / 244 = 3.93 gms of O2

Balanced chemical equation: CaCO3 → CO2 + CaO
Molecular weight: 40 + 12 + (3 × 16) = [12 + (2 × 16)] + (40 + 16)
or, 100 = 44 + 56
100 gms of CaCO3 gives 44 gms of CO2 and 56 gms of CaO
1 gm of CaCO3 gives 44/100 gms of CO2 and 56/100gms of CaO
10 gms of CaCO3 gives 44/100 ×10 gms of CO2 and 56/100 ×10 gms of CaO
So, 10 gms of CaCO3 gives 4.4 gms of CO2 and 5.6 gms of CaO.

Balanced chemical equation: 2Mg + O2 → 2MgO
Molecular weight: (2 × 24) + (2 × 16) = 2 (24 + 16)
or, 48 + 32 = 80

48 gm of Mg gives 80 gm of MgO
or, 1 gm of Mg gives 80/48 gm of MgO
or, 10 gm of Mg gives 80/48 × 10 gm of MgO
So, 10 gm of Mg gives 16.66 gm of MgO.

Here, balanced chemical equation: 2KOH + H2SO4 → K2SO4 + 2H2O
Molecular weight:
2 (39 + 16+ 1) + [(2 × 1) + 32 + (4 × 16)] = [(39 × 2) + 32 + (4 × 16)] + 2 [(2 × 1) + 16]
or, 112 + 98 = 174 + 36
112 gm of KOH gives 174 gm of K2SO4
1 gm of KOH gives 174/112 gm of K2SO4
10 gm of KOH gives 174/112 × 10 gm of K2SO4
So, 10 gm of KOH gives 15.32 gm of K2SO4

When the concentration of reacting compounds is increased, the reacting molecules become close together due to increase of the number of reacting molecules. As the result, the reacting molecules collide together to increase the rate of chemical reaction.

The amount of the reactant that is converted into the product in per unit time is called the rate of chemical reaction.

When the temperature of the reactants increases, the kinetic energy of the molecules of the reactants also increases. As the result, the molecules of the reactants collide together faster to increase the rate of chemical reaction.

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  • The sum total of the number of protons and neutrons present in the nucleus of an atom is called _______.

    Atomic weight
    Molecular weight
    Avogrado Number
    Gram Molecular weight
  • What is the molecular weight of water?

    18
    15
    17
    16
  • The gram molecular weight of CaCO3 is.....

    200gm
    Can't say
    150gm
    100gm
  • _______ is the collection of 6.023 x 1023 particles or ions or atoms of a substance.

    Atomic mass
    Mole
    Atomic weight
    Avogrado Number
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Shikshya

What is 4 mile of carbon dioxide?


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Anzila

How many moles is there in 110gm of co2 ?


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