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3) A salt is a compound which is formed by neutralization reaction between an acid and base.

e.g. sodium chloride.

  1. Indicators – Indicators are substances which indicate the acidic or basic nature of the solution

by their colour change.

The colour of some acid – base indicators in acidic and basic medium are given below

Sr. No.





Litmus solution




Methyl Orange








Methyl red



5) Chemical properties of acids:

i) Acids react with active metals to give hydrogen gas.

Zn + H2SO4 ZnSO4 + H2

ii) Acids react with metal carbonate and metal hydrogen carbonate to give carbon dioxide.

NaHCO3 +HCl NaCl + H2O + CO2

iii) Acids react with bases to give salt and water. This reaction is called as neutralization reaction.

NaOH + HCl  NaCl +H2O

iv) Acids react with metals oxides to give salt and water.

CuO + H2SO4  CuSO4 + H2O

6) Chemical properties of Bases:

i) Reaction with Metals - Certain reactive metals such as Zinc, Aluminium, and Tin react with alkali solutions on heating and hydrogen gas is evolved.

2NaOH + Zn  Na2ZnO2 +H2

ii) Reaction with acids -Bases react with acids to form salt and water.

KOH +HCl  KCl +H2O

iii) Reaction with Non -metallic oxides – These oxides are generally acidic in nature. They react with bases to form salt and water.

2NaOH + CO2  Na2CO3 + H2O

7) PH Scale: The concentration of hydrogen ion in solution is expressed in terms of pH. The pH of a solution is defined as the negative logarithm of hydrogen ion concentration in moles per liter.

pH = - log [H+]

For water or neutral solutions, pH = 7 ; For acidic solutions, pH < 7; For basic solutions, pH > 7

8) Some Important Chemical Compounds:
a) Common Salt (NaCl)

Sodium chloride is known as common salt. Its main source is sea water. It is also exists in the form of rocks and is called rock salt.

Common salt is an important component of our food. It is also used for preparing sodium hydroxide, baking soda, washing soda etc.

b) Sodium Hydroxide or Caustic Soda (NaOH)

It is prepared by passing electricity through an aqueous solution of sodium chloride also known as brine.

2NaCl (aq) + 2 H2O (l)  2NaOH (aq) + Cl2 (g) + H2 (g)

This process is known as chlor-alkali process.


1. It is white translucent solid.

2. Crystals of sodium hydroxide are deliquescent.

3. It is readily soluble in water and gives strong alkaline solution.

c) Bleaching Powder (CaOCl2)

Its chemical name is calcium oxychloride. It is prepared by passing chlorine gas through dry slaked lime.

Ca (OH) 2 + Cl2 CaOCl2 + H2O

Uses –

1. For bleaching cotton and linen in textile industry and wood pulp in paper industry

2. For disinfecting drinking water.
d) Baking Soda (NaHCO3)

Chemical name is Sodium hydrogen carbonate.

It is prepared by passing CO2 gas through brine solution saturated with ammonia.

NaCl + H2O +CO2 +NH3  NH4Cl + NaHCO3


1. It is white crystalline solid and sparingly soluble in water at room temperature.

2. On heating it decomposes to give sodium carbonate and carbon dioxide.

3. It reacts with acids to give carbon dioxide gas.

4. It aqueous solution is weak alkaline due to hydrolysis.


1. It is used in soda – acid fire extinguisher.

2. It acts as mild antiseptic and antacid.

3. It is used as a component of baking powder. In addition to sodium hydrogen carbonate baking soda contains tartaric acid.

e) Washing Soda (Na2CO3.10 H2O)

Chemical name is sodium carbonate decahydrate.

It is prepared by heating baking soda. Recrystallisation of sodium carbonate gives washing soda.

2NaHCO3  Na2CO3 +H2O +CO2

Na2CO3 +10 H2O  Na2CO3. 10 H2O


1. It is used for removing permanent hardness of water.

2. It is used in glass, soap and paper industries.

3. It can be used as a cleaning agent for domestic purposes.

f) Plaster of Paris (CaSO4.1/2H2O)

Its chemical name is calcium sulphate hemihydrates. It is obtained by heating Gypsum upto 373K.

CaSO4.2H2O  CaSO4.1/2H2O + 11/2H2O

On treatment with water it is again converted into gypsum and sets as a hard mass.



  1. It is used by doctors for setting fractured bones.

  2. It is used for making statues, models and other decorative materials.




Blue litmus red

Sour to taste

Give H+ ions


Soapy to touch

Red litmus blue

Bitter to taste

Gives OH¯ ions





Indicates whether a substance is acid basic or neutral

pH Scale


Formed when an acid and a base reacts with each other

Common salt


Bleaching powder


Baking soda


Washing soda


Plaster of paris





  • Questions : 1 to 5 – 1 Mark each

  • Questions : 6 to 9 – 2 Marks each

  • Questions : 10 to 13 – 3 Marks each

  • Question 14 – 5 Marks

  1. Name the gas formed when sodium hydroxide reacts with zinc.

  2. Write the chemical name of baking soda.

  3. What happens when gypsum is heated at 373K?

  4. Which has a higher pH value 1M HCl or 1M NaOH solution?

  5. Hydrogen ion concentration of an acid is 1 x 10-2 mol/l. what is its pH?

  6. What is meant by ‘Water of Crystallisation’ of a substance? Describe an activity to show that.

  7. Why does tooth decay start when the pH of mouth is lower than 5.5?

  8. What is baking powder? How does it make the cake soft and spongy?

  9. Give Arrhenius definition of an acid and a base. Choose strong acid and strong base from the following:


  1. What happens when nitric acid is added to egg shell? Give the chemical equation.

  2. A student prepared solutions of an acid and a base in two separate beakers. She forgot to label the solutions and litmus paper is not available in the laboratory. Since both the solutions are colourless, how will she distinguish between the two?

  3. Identify the compound ‘X’ on the basis of the reactions given below. Write the names and chemical formulae of A, B, C

    + Zn

    1. + H2 (g)

    Compound X


    1. + H2O

    + CH3COOH

    1. + H2O

  4. How is plaster of Paris prepared? What is its chemical formula? Write is chemical name.

    1. Define strong acid and weak acid.

    2. A student working in the laboratory added some water to a syrupy liquid taken in tube. The tube immediately cracked and the liquid escaped out, that produced blisters on the skin of the student. Why?



In one of the industrial process used for manufacture of sodium hydroxide, a gas ‘X’ is formed as by – product. The gas ‘X’ reacts with lime water to give a compound ‘Y’ which is used as a bleaching agent in chemical industry. Identify ‘X’ and ‘Y’ giving the chemical equation of the reaction.


In the manufacture of sodium hydroxide, hydrogen gas and chlorine gas (X) are formed as by products. When chlorine gas (X) reacts with lime water, it forms calcium oxy chloride (bleaching powder) Y.

2NaCl (aq) + 2 H2O (L) 2NaOH (Aq) + Cl2 (G) + H2 (G)

‘X’  Cl2 gas

Ca(OH)2 + Cl2 CaOCl2 + H2O


Dry hydrogen chloride gas does not turn blue litmus, whereas hydrochloric acid does. Why?


In the dry state, hydrogen chloride (HCl) does not release H+ ions. Therefore, it cannot behave as an acid. When dissolved in water, it forms hydrochloric acid. It dissociates to give H+ ions in solution and behaves as an acid.


Acid when react with metals release hydrogen gas but there is one acid which when reacts with metals does not release hydrogen except for two metals. Prove this statement.


Acid + Metal  Salt + Hydrogen

e.g. 2HCl + 2Na  2NaCl + H2

H2SO4 + 2Na  Na2SO4 + H2

HNO3 + Na  No hydrogen gas.

Because nitric acid is strong oxidising agent. Nitric acid reacts only with Mg and Mn to give hydrogen gas.

Mg + 2HNO3 Mg(NO3)2 + H2

Mn + 2HNO3Mn(NO3)2 + H2

Q. 4

Name the properties responsible for the following uses of baling powder. (i) Baking industry (ii) As an antacid (ii) As soda-acid fire extinguisher.

Q. 5

What is meant by water of crystallisation of a substance? What is its importance?

Q. 6

What effect does an increase in concentration of ‘H’ ions in a solution have on the pH of a solution

Q. 7

Fresh milk has a pH Of 6. When it changes to curd, will its pH value increase or decrease? Why?

Q. 8

How does the flow of acid rain water into a river make the survival of aquatic life in a river difficult?

Q. 9

Arrange in the increasing order of their pH values: NaOH solution, Blood, Lemon juice,

Q. 10

Two solutions A and B have pH values of 5 and 8 respectively. Which solution will be basic in nature?

Q. 11

Why does an aqueous solution of acid conduct electricity?

Q. 12

How is alkali different from a base?

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