Class 10 Notes - ACIDS, BASES AND SALTS

1)      Acids are sour in taste, turn blue litmus red, and dissolve in water to release H⁺ ions e.g. HCl, H₂SO₄, HNO₃ etc.

2)      Bases are bitter in taste, have soapy touch, turn red litmus blue and give hydroxide ions in solution.

e.g.  NaOH, KOH etc.

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

             e.g. sodium chloride.

3)      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.	INDICATORS	COLOUR IN ACIDIC MEDIUM	COLOUR IN BASIC MEDIUM
1	Litmus solution	Red	Blue
2	Methyl Orange	Pink	Orange
3	Phenolphthalein	Colourless	Pink
4	Methyl red	Yellow	Red

                            

5) Chemical properties of acids:

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

                     Zn + H₂SO₄àZnSO₄ + H₂

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

                    NaHCO₃ +HCl àNaCl + H₂O + CO₂

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

                    NaOH + HCl à NaCl +H₂O

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

                   CuO + H₂SO₄ à 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 à  Na₂ZnO₂ +H₂

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

                           KOH +HCl à 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 + CO₂à 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) à 2NaOH (aq) + Cl₂ (g) + H₂ (g)

This process is known as chlor-alkali process.

Properties:

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 + Cl₂àCaOCl₂ + 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 +NH₃à NH₄Cl + NaHCO₃

Properties:

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.

Uses:

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.

                     2NaHCO₃à Na₂CO₃ +H₂O +CO₂

                     Na₂CO₃ +10 H₂O  à Na₂CO₃. 10 H₂O

Uses:

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 à CaSO₄._1/2H₂O + 1_1/2H₂O

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

CaSO₄._1/2H₂O+1_1/2H₂OàCaSO₄.2H₂O

Uses:-

1. It is used by doctors for setting fractured bones.
2. It is used for making statues, models and other decorative materials.

Class 10 Notes - CHEMICAL REACTION AND EQUATIONS

 1)Chemical reaction—   Chemical changes or chemical reactions are the changes in

which one or more new substances are formed.

2)Chemical Equations – Representation of a chemical reaction in terms of symbols and

formulae of the reactants and products is known as chemical equation.

     3)Balanced Chemical equations – The chemical equation in which the no. of atoms of different

elements is same on both sides of the arrow is called balanced chemical equation.

 4) The chemical reactions can be classified into different types such as—

a)      Combination reaction – The reactions in which two or more substances combine to form a new substance are called combination reaction. For example,

       2Mg(s) + O₂ (g)  à  2 MgO (s)

b)     Decomposition reaction - The reaction in which a single compound breaks up into two or more simpler substances are called decomposition reactions. For example,

2Pb (NO₃)₂ (s) à 2PbO (s) + 4NO₂ (g) +O₂ (g)

The decomposition of a substance by passing electric current through it is known as electrolysis (Electrical Decomposition).

The decomposition of a substance on heating is known as thermal decomposition.

The decomposition of a substance by absorbing light energy is called photochemical decomposition.

c)      Displacement reactions -The chemical reactions in which a more reactive element displaces a less reactive element from a compound are known as displacement reactions. For example,

i)                    Zn (s) + CuSO₄ (aq)  à ZnSO₄ (aq) + Cu (s).

ii)                  Cu (s) + 2AgNO₃ (aq) à Cu (NO₃)₂ (aq) +2Ag (s).

d)     Double Displacement Reactions - The chemical reactions in which compounds react to form two different compounds by mutual exchange of ions are called double displacement reactions.

These reactions take place in solution two common types of this reaction are precipitation reactions and neutralization reactions

i)                    Precipitation reaction : In this reactions, aqueous solution of two salts are mixed whereby 

Some salts precipitate due to mutual exchange of ions between the two salts. For example

                          AgNO₃ (aq) + NaCI (aq) -----> AgCl(s) + NaNO₃.

ii)                  Neutralization reaction: In this type of reaction an acid reacts with a base to form salt and water by exchange of ions.

                                       NaOH (aq) + HCl (aq) à NaCl (aq) + H₂O.

e)      Redox reaction: Chemical reaction which shows both oxidation and reduction reaction.

Oxidation: Reaction that involves the gain of oxygen or loss of hydrogen.

Reduction: Reaction that shows the loss of oxygen or gain of hydrogen.

    Both oxidation and reduction take place simultaneously and hence called redox reaction.

                                                 ZnO + C à Zn +CO

                                                ZnO reduce to Zn ---- reduction

                                                C oxidize to CO ------oxidation

f)Exothermic reaction and endothermic reaction:  On the basis of energy changes during chemical

reaction, they can be classified as

i)                    Exothermic reaction: A chemical reaction in which heat energy is produced.

                             C + O₂à CO₂ (g) + heat

ii)                  Endothermic reaction: A chemical reaction in which heat energy is absorbed.

                  CaCO₃ + Heat à CaO + CO₂

5 Corrosion – The process of slow conversion of metals into their undesirable compounds due to their reaction with oxygen, water, acids, gases etc. present in the atmosphere is called corrosion.

Rusting – Iron when reacts with oxygen and moisture forms red substance called rust. Chemical composition of rust is Fe₂O₃.xH₂O. Its chemical name is Hydrated Iron (III) oxide.

6 Rancidity – The taste and odour of food materials containing fat and oil changes when they are left exposed to air for long time. This is called rancidity. It is caused due to oxidation of fat and oil present in food material.

It can be prevented by using various methods such as by adding antioxidants to the food materials. Storing food in air tight container and by flushing out air with nitrogen.