ICSE Class 10 Chemistry Chapter 05 Mole Concept and Stoichiometry

Chapter 5: Mole Concept and Stoichiometry

Important Points to Remember

1. Gay Lussac's law - whenever the gases combine chemically, they do so in volumes which bear a simple ratio to each other as well as to the product if gaseous, under the same conditions of temperature and pressure.

2. Gay Lussac published the result of his experiment on different gases under the name: "The Law of Combining Volumes of Gases".

3. Gay Lussac's law is applicable only to gases and not to solids and liquids.

4. Atomic weight is the number which represents how many times one atom of a substance is heavier than 1/12th the mass of an atom of Carbon -12.

5. Molecular weight is the number which represents how many times one molecule of a substance is heavier than 1/12th the mass of an atom of Carbon -12.

6. Molecular weight expressed in grams is called gram molecular weight.

7. Avogadro's Law - According to Avogadro, under the similar conditions of temperature and pressure, equal volumes of all gases contain equal number of molecules.

8. The volume occupied by one mole of a gas at S.T.P. (Standard Temperature and Pressure) is called molar volume. It is equal to 22.4 dm³ or 22.4 litres.

9. The gram molecular weight of all gases at S.T.P. contains molecules equal to Avogadro's number which is 6.023 × 10²³ and it occupies a volume equal to molar volume which is 22.4 dm³ or 22.4 litres.

10. Number of moles = \[\frac{\text{Weight in grams of the substance}(W)}{\text{Molecular weight of the substance}(M)}\]

Or \[n = \frac{W}{M}\]

11. Number of molecules = No. of moles × Avogadro's number

12. The relationship between mole, gram molecular weight, molar volume, and number of molecules can be summarized as follows:

13. Atomicity is the number of atoms present in one molecule of an element.

14. Metals are monoatomic, i.e., containing one atom in its molecule.

Teacher's Note

When you bake a cake, the leavening agent (baking soda) reacts in precise proportions - just like how gases combine in simple volume ratios according to Gay-Lussac's law, showing how chemistry's laws help recipes work perfectly every time.

Continuation of Important Points

15. Inert gases are monoatomic.

16. Gases like Hydrogen (H₂), Oxygen (O₂), Nitrogen (N₂) are diatomic, i.e., containing two atoms in its molecule.

17. The elements containing more than two atoms in its molecule are called as polyatomic. Example - Ozone: O₃, Phosphorus: P₄, Sulphur: S₈

18. Vapour density is the ratio between the mass of certain volume of gas or vapour to the mass of same volume of hydrogen under the similar conditions of temperature and pressure.

\[\text{Vapour density} = \frac{\text{Mass of certain volume of gas or vapour}}{\text{Mass of same volume of Hydrogen}}\]

19. Vapour density is a ratio, so it has no units.

20. \[\text{Molecular weight} = 2 \times \text{Vapour density}\]

21. The percentage composition of a compound is defined as the percentage by weight of each element present in the molecule of a compound.

\[\text{Percentage composition of a compound} = \frac{\text{Weight of an element in a molecule of a compound}}{\text{Gram molecular weight of compound}} \times 100\]

22. Empirical formula is the formula of a chemical substance which tells the simplest whole number ratio of the atoms of different elements present in its one molecule.

23. Molecular formula is the formula of a chemical substance which represents the actual number of atoms of each element present in its single molecule.

24. In a chemical equation, reactants are written on the left side of the arrow and products are written on the right side of the arrow.

Reactants - Products

25. For the calculation of the numericals based on equation, the equation must be completely balanced.

26. The molecular weights of the products and reactants must be calculated which are required for solving the numerical.

27. Unitary Method is used to find the weight of product or reactant as per the requirement of the problem.

28. In case of gases, the volume required is 22.4 dm³ for every mole of a gas.

\[\text{Relative Atomic Mass} = \frac{\text{Mass of one atom of an element}}{\text{1/12th of mass of an atom of carbon-12}}\]

29. Relative atomic mass can also be defined with respect to hydrogen. It is the number that represents, how many times one atom of an element is heavier than one atom of hydrogen, whose weight has been taken as unity.

\[\text{Relative Atomic Mass} = \frac{\text{Mass of one atom of an element}}{\text{Mass of one atom of hydrogen (weight taken as unity)}}\]

30. The relative atomic mass of an element expressed in grams is called gram atomic mass or gram atom.

31. \[\text{Relative Molecular Mass} = \frac{\text{Mass of one molecule of a substance}}{\text{Mass of 1/12 th of an atom of C-12}}\]

32. Relative molecular mass can also be defined with respect to hydrogen. It is the number that represents how many times one molecule of a substance is heavier than one atom of hydrogen whose weight is taken as unity.

Teacher's Note

Understanding molecular formulas helps us determine exactly how much medicine to prescribe - the ratio of atoms in a drug molecule determines its effectiveness and safety, showing how chemistry directly impacts healthcare decisions.

This is a preview of the first 3 pages. To get the complete book, click below.