NCERT Class 10 Basic concepts of chapter—2

Basic concepts of Acids, Bases and Salts

1. Acids are sour in taste and change the colour of blue litmus to red.

2. Bases are bitter in taste and change the colour of red litmus to blue.

3. Acids and some bases react with active metals and give out hydrogen gas with the formation of salt.

4. Acids react with sodium carbonate or bicarbonate to give carbon dioxide gas.

5. Acids neutralize bases or metal oxides to give corresponding salt and water.

6. All acids generate H+ ions and all bases generate OH- ions in the presence of water and this helps acids and bases to conduct electricity.

7. The amount of H+ ions or OH- ions in a solution can be measured by the PH scale.

8. The PH of a neutral solution is 7. Values less than 7 represent an acidic solution while more than 7 an alkaline solution.

9. Values of pH are very important in living organisms and our digestive system.

10. Mixing strong nitric acid and strong sulphuric acid with water is a highly exothermic process.

11. Water of crystallization is a definite number of water molecules attached to each formula unit of a salt in its crystalline form.

12. Salt of hydrochloric acid and sodium hydroxide is sodium chloride. It is an important raw material for preparing materials used in everyday life and in industries.

13. Sodium carbonate is obtained by Solvay-ammonia process, i.e., by passing CO2 through sodium chloride saturated with ammonia. The reaction takes place in the following steps: 

             CaCO3 —–› CaO + CO2

    (i) NH3 + H2O + CO2 —–› NH4HCO3

                                                 Ammonium 

                                                 bicarbonate

   (ii) NH4HCO3 + NaCl —–› NH4Cl + NaHCO3

                                                                Sodium

                                                          bicarbonate

   (iii) 2NaHCO3 —–› Na2CO3 + H2O + CO2

Ammonia (as ammonium chloride) and carbon dioxide are regenerated and so only limestone and sodium chloride are consumed to produce sodium carbonate.

Sodium carbonate is mainly used in detergents and softening of hard Water.

14. Sodium hydroxide is an important alkali used for laboratory work. It is produced by electrolysis of sodium chloride (chlor-alkali process).

15. Baking powder is chemically sodium bicarbonate. It is used as a cooking agent and in fire extinguishers as per the following reaction:   

2NaHCO3 +H2SO4 —–›Na2SO4+2H2O+ 2CO2

A stream of CO2 is produced which cuts of the supply of air and thus fire is extinguished. 

 

16. Bleaching powder is calcium oxychloride. This is prepared by passing Chlorine gas over slaked lime for a long time.

     Ca(OH)2 + Cl2 —–› CaOCl2 + H2O

It is mainly used for bleaching clothes and for disinfecting drinking water.

17. CaSO4.1/2H2O is known as plaster of Paris. When watted with water it sets to hard porous mass within 10-15 minutes. It is prepared by heating gypsum to 120- 130°C.

18. The interaction of a salt with water to give an acid and a base is called salt hydrolysis.

19. The solution obtained as a result of hydrolysis may be acidic, basic or neutral depending upon the nature of salt.

20. Salts of strong acid and strong base like sodium chloride (NaCl), sodium sulphate (Na2SO4) give neutral solution. Salts of weak base and strong acid like ammonium chloride (Nh4Cl), copper sulphate (CuSO4) give acidic solution. Salts of weak acid and strong base like sodium carbonate (Na2CO3), Potassium acetate (CH3COOK) give basic solution.