Acids, Bases and Salts class 10 notes 2021

 Acids  

Substances which are sour in taste and turns blue litmus paper into to red are called acids.  Some common fruits like lemon, orange, tamarind etc. are sour in taste. Acids gives H+ ions when dissolve in water. 

Chemical Properties of Acids

(i) When acid reacts with metal it gives salt and hydrogen.  

Example -  2HCL + Zn  ⟶  ZnCl2 + H2

(ii)  When acid reacts with metal carbonates or metal hydrogen carbonates it gives salt, carbon dioxide and water 

Example •  2HCL + Na2 CO3   ⟶  2NaCl2 + CO2 + H2O

•  HCL + 2NaHCO3  ⟶  NaCL + CO2 + H2O

(iii) When acid reacts with metallic oxide  it  gives salt and water.

Example -  2HCL + CaO   ⟶  CaCl2  + H2O

(iv) Strong acid like (HCL, H2SO4, HNO3  etc.) are completely ionised in water while weak acid line (H2S, HCN, etc.) ionises partially in water.

Some naturally occurring acids are :

Bases 

Substances which are bitter  in taste and turns red litmus paper into to blue are called bases. When bases are dissolve in water it gives  (OH-)  ions

Chemical properties of Bases

(i) When base reacts with metal it gives salt and hydrogen.

Example -  2NaOH + Zn   ⟶  Na2ZnO2 + H2

(ii) When base reacts with non - metallic oxide it gives salt and water.

Example -  Ca(OH)2 + CO2 ⟶  CaCO3 + H2O

(iii) Bases does not react with metal and metal hydrogen carbonates because metals carbonates are itself base so, base reaction with base it gives no reaction.

(iv) Strong bases like NaOH, KOH etc. melt on heating while weak bases like NH4OH, Mg(OH)2 are decompose on heating.   

Acids and Base in Water Solution

In the presence of water, acids gives H positive ions. As H⁺ ion cannot exist alone, so it combines with water molecules and form H3O+ (hydronium ion.)

Example -   HCl + H2O ⟶ H3O⁺  + Cl-

H⁺ +  H2O  ⟶  H3O⁺

Reaction between acid and base

When acid and base reacts which each other and forms salt and water, that reaction is known as neutralization reaction.

Example -   HCl +NaOH   ⟶ NaCl + H2O

^Dilution 

Mixing of acid or base with water is called dilution. It decrease in the concentration of ions per unit volume.

Indicator

Indicator are those substances that change their color when added in acidic and basic solution.

Types of Indicator 

1. Natural Indicator 

These  Indicator are found in nature in the plants e.g. Litmus solution is a purple color dye extracted from the lichen plant. 

2. Synthetic Indicator 

These  Indicator are used in laboratory or industry are known as  Synthetic Indicator. 

 

3. Olfactory  Indicator  

Those substance change their smell when came contact in acid and base.

4. Universal Indicator 

It is mixture of several indicators and it show different color at different concentration of Hydrogen positive ions in the solutions.

pH scale 

pH scale is used to measuring hydrogen ions concentration. It has values ranging from 0 very acidic to 14 very alkaline. pH is a number which indicates the acidic or basic nature of solution.

* If pH is greater than 7 then it is basic solution.

* If pH is less than  than 7 then it is acidic solution.

* If pH is equal to 7 then it is neutral.

 

Importance of pH is Everyday Life

(i) Plants and Animals are pH Sensitive

Our body works normally within a pH range of 7.0 to 7.8. When pH of water goes below 5.6 it is called acid rain if pH of rain water less than 5.6 then it harmful of aquatic animal.

(ii) pH of the Soil

Nature  of  soil  is  known  by  testing  its  pH  and  then  a  particular  crop  is  grown  in  it  by selecting fertilizer.

(iii) pH is our digestive System 

During indigestion our stomach produce to much gases it cause pain and irritation to prevent from this we use eno because eno have present antacid.

(iv) pH of Tooth Decay

If the pH of our teeth less than 5.5 then it becomes decaying to prevent from this we using toothpaste after eating because toothpaste is basic which neutralise the acid. 

(v) Self defence by animal

When honeybee bite we feel pain because it inject acid into skin and produce methanoic acid to prevent from this we use baking soda applied on effected area, it gives relief.

Salts

Salts are produced by sodium chloride and sodium hydroxide / neutralization reaction.

Salts are strong acid and base neutral with pH value of 7.

Properties of Salts and Uses

1. Sodium hydroxide
2. Bleaching powder
3. Baking Soda
4. Washing Soda
5. Plaster of Paris

Sodium hydroxide

Chemical Name - Sodium hydroxide

Common Name - Caustic Soda

Molecular Formula - NaOH

Preparation Method of Sodium hydroxide

When electricity is passed through an aqueous solution of NaCl it decompose to form sodium hydroxide, this process is called chlor- alkali process.

Reaction 

Uses:

(i) It is used to make soap and detergents.

(ii) It is used in oil refining.

(iii) It is used paper manufacture.

(iv) It is used pesticides.

(v) It is also used in purification of petroleum and bauxite refining. 

 Bleaching powder

Chemical Name - Calcium hypochlorite

Common Name - Bleaching powder

Molecular Formula - CaOCl2

Preparation Method Bleaching powder

It is produced by the action of chlorine on dry slaked lime.

Reaction

 Uses :

(i) It is used to cleaning process of sugar.

(ii) It is used for manufacture chloroform.

(iii) It is used to disinfecting in water.

(iv) It is used agent for cotton, linen and wood pulp.

Baking Soda

Chemical Name - Sodium bicarbonate

Common Name - Baking soda

Molecular Formula - NaHCO3 

Preparation Method Baking Soda

It is prepared by using sodium chloride as one of the raw material.

Reaction

Uses :

(i) It is used an ingredient antacid.

(ii) It is used in fire extinguisher.

(iii) It is used for making baking powder which is mixture of baking soda and tartaric acid.

(iv) It is used in medicines.

When Baking soda is heated

 NaHCO3 + HCl →  NaCl + CO2 + H2O

 Washing Soda

Chemical Name - Sodium Carbonate

Common Name - Soda ash

Molecular Formula - Na2CO3 . 10H2O

Preparation Method of Washing soda

Sodium Carbonate can be obtained by heating baking soda. The recrystallisation of sodium carbonate gives washing soda. It is also basic salt.

Reaction

 

Uses :

(i) It is used washing purpose.

(ii) It is used to removing permanent hardness of water.

(iii) It is used in medicine eye.

(iv) It is used to making glass, detergent caustic soda etc.

Plaster of Paris

Chemical Name - Calcium sulphate hemihydrate

Common Name - Plaster of paris

Preparation Method Plaster of paris

When calcium sulphate dihydrate is heated at 373K, plaster of paris is formed by dehydration.

Plaster of paris is a white powder and on mixing with it changes into gypsum giving a hard solid mass.

Reaction

Uses :

(i) It is used to join broken bones.

(i) It is used to making toys and others decorative material.

(i) It is used to making surface smooth.