ICSE Class 10 Chemistry Chapter 03 Study of Acids Bases and Salts

Chapter 3

Study of Acids, Bases and Salts

Important Points To Remember

1. Acids: The chemical compounds which on dissolving in water produce Hydrogen ions or Hydronium ions as the only positively charged particles. All acids essentially contain Hydrogen.

2. Hydronium ion: Hydronium ion is hydrated hydrogen ion. When hydrogen ion combines with water molecule it forms ionized hydrogen ion called hydronium ion. The formation of hydronium ion takes place by the coordinate bond formation. In water molecule, oxygen atom has two lone pairs of electrons, oxygen atom shares one of its lone pair of electrons to hydrogen ion to complete its doublet thereby the formation of hydronium ion takes place.

(i) Formation of Water molecule

H-O-H with lone pair of electrons shown, and H-O-H structure with lone pair of electrons labeled.

(ii) Formation of Hydrogen ion (H+)

H - e- - H+

(iii) Formation of Hydronium ion

H2O + H+ - H3O+

H-O-H with H below and coordinate bond shown, forming Hydronium ion with H-O-H and H structure.

3. Acids can be classified on the basis of

(i) Strength of an acid - (ii) Basicity of an acid - (iii) Concentration

4. Strong acids are those which almost completely ionized in their aqueous solutions. The solution of strong acid contains mostly ions. e.g., Hydrochloric acid (HCl), Sulphuric acid (H2SO4), Nitric acid (HNO3).

5. Weak acids are those which partially or incompletely ionized in their aqueous solutions. The solution of weak acids contains ions as well as molecules. e.g., Acetic acid (CH3COOH), Sulphurous acid (H2SO3), Carbonic acid (H2CO3).

6. Basicity of an acid is defined as the number of replaceable Hydrogen ions present per molecule of an acid in its aqueous solution.

7. Monobasic acids: Acids which contain only one replaceable Hydrogen ion per molecule are called Monobasic acids. e.g., HCl, HNO3, HNO3, CH3COOH

Monobasic acids form single series of salts, i.e., normal salts

NaOH + HCl - NaCl + H2O

HCl - H+ + Cl-

NaOH + HNO3 - NaNO3 + H2O

HNO3 - H+ + NO3-

NaOH + CH3COOH - CH3COONa + H2O

CH3COOH - CH3COO- + H+

Teacher's Note

Acids are found in everyday products like vinegar (acetic acid) and lemon juice (citric acid), which is why these foods taste sour and can be used in cooking and cleaning.

8. The names of the salts formed by some monobasic acids are given below:

9. Dibasic acids are those which contain two replaceable Hydrogen ions per molecule of an acid in its aqueous solution. e.g., H2SO4, H2SO3, H2CO3, etc.

For example (i) Ionization of Sulphuric acid

H2SO4 - H+ + HSO4-

HSO4- - H+ + SO42-

H2SO4 - 2H+ + SO42-

Dibasic acids form two series of salts, one acid salt and one normal salt

NaOH + H2SO4 - NaHSO4 + H2O

Sodium bisulphate (Acid salt)

NaHSO4 + NaOH - Na2SO4 + H2O

Sodium sulphate (Normal salt)

(ii) The ionization/dissociation of sulphurous acid

H2SO3 - H+ + HSO3-

HSO3- - H+ + SO32-

H2SO3 - 2H+ + SO32-

NaOH + H2SO3 - NaHSO3 + H2O

Sodium bisulphite

NaHSO3 + NaOH - Na2SO3 + H2O

Sodium sulphite

10. The names of the salts formed by some dibasic acids are given below:

11. Tribasic acids: The acids which ionize on dissolving in water to produce three replaceable Hydrogen ions per molecule of an acid are called tribasic acids. e.g., H3PO4.

Ionization of Phosphoric acid

H3PO4 - H+ + H2PO4-

H2PO4- - H+ + HPO42-

HPO42- - H+ + PO43-

H3PO4 - 3H+ + PO43-

Tribasic acids form two different acid salts and one normal salt.

NaOH + H3PO4 - NaH2PO4 + H2O

(Acid salt)

NaH2PO4 + NaOH - Na2HPO4 + H2O

(Acid salt)

Na2HPO4 + NaOH - Na3PO4 + H2O

(Normal salt)

12. Concentration of an acid is the measure of the amount of water present in the acid.

13. Concentrated acid contains negligible quantities of water.

14. Dilute acid contains more quantity of water and less quantity of acid.

15. Strong acid will remains strong even if the solution is diluted and weak acid will remains weak even if the solution is concentrated.

16. Methods of preparation of acids: Acids are generally prepared by the following methods:

(a) By synthesis or direct combination:

H2 + Cl2 - 2HCl

Hydrogen - Chlorine - Hydrochloric acid

H2 + Br2 - 2HBr

Hydrogen - Bromine - Hydrobromic acid

H2 + S - H2S

Hydrogen - Boiling sulphur - Hydrogen sulphide

(b) By dissolving acidic oxide or acid anhydride in water:

Acidic oxides are also called as acid anhydrides. Acidic oxides on dissolving in water produces acids.

CO2 + H2O - H2CO3

Carbon dioxide - Carbonic acid

SO2 + H2O - H2SO3

Sulphur dioxide - Sulphurous acid

P2O5 + 3H2O - 2H3PO4

Phosphorus pentaoxide - Phosphoric acid

2NO2 + H2O - HNO2 + HNO3

Nitrogen dioxide - Nitrous acid - Nitric acid

(c) By the reaction of non-volatile acid with the salts of more volatile acids:

Concentrated sulphuric acid is the non-volatile or least volatile acid which reacts with metallic nitrates and metallic chlorides to form Nitric acid and Hydrochloric acid respectively.

Teacher's Note

The preparation of acids in the laboratory mirrors industrial processes, showing how chemistry knowledge directly applies to manufacturing important chemicals we use daily.

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