Class 10 Science Notes (Class 10)

Acid Bases And Salt – CBSE Class 10 Science Chapter 2

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Acid Bases and Salts

Acid Bases and Salts

Acid Bases and Salts

Introduction

Acids: All acids are sour in taste. 
Type of acids: 

(i) Natural acids: This type of acid is obtained from natural sources e.g Ascorbic acid (Amla and Guava), Lactic acid (Milk), Citric acid (Lemon and Orange) etc.

(ii) Mineral acids: Such type of acid is obtained from minerals e.g Hydrochloric acid, Sulphuric acid and Nitric acid. 

Properties of Acids

(i) Acids are sour in taste.
(ii) All acids give (H+) hydrogen ion with water. 
(iii) It turns the colour of blue litmus to red. 
(iv) Acids conduct electrical current.
(v) It reacts with metals produces salt and hydrogen gas. 
(vi)Bases are bitter in taste and soapy touch. 
 

Properties of Bases

(i) Bases are bitter in taste.
(ii) All bases give (OH ) hydroxide ion with water.
(iii) It turns the colour of red litmus to blue. 
(iv) Bases conduct electrical current. 
(v) It also reacts with metals gives salt and hydrogen gas.

Types of Indicators and its Properties

Indicators: Substance which changes their colour/smell in different types of substance (acids & bases)_.
Types of Indicators
 
(i) Natural Indicators: Found in nature in plants. Example: Litmus, red cabbage leaf extract, flowers of hydrangea plant, turmeric.
(ii) Synthetic Indicators: These are chemical substances. Example: Methyl orange, phenolphthalein.
(iii) Olfactory Indicators: These substances have a different odour in acid and base.

The reaction of Acids & Bases with Metals

  • Acids react with the metal to form metal salt and release Hydrogen Gas.

Acid + Metal → Hydrogen Gas

  • Example: Zinc granules react with dilute Hydrochloric Acid in a test tube.

2HCl + Zn = ZnCl2 + H2

 

The reaction of Base with Metal

  • Bases react with the metal to evolve hydrogen gas. Also, note that all metal does not react with bases. The metal must be more reactive than the metals present in the base for the reaction to take place.

Base + Metal → Salt + Hydrogen Gas

  • Example: Zinc granules react with NaOH solution to form Sodium Zincate & evolve Hydrogen Gas.

2NaOH + Zn = Na2ZnO2 + H2

  • Hydrogen Gas released can be tested by bringing a burning candle near gas bubbles, it burst with a pop sound.

The reaction of Acids with Metal Carbonates and Metal Hydrogencarbonates

  • Acids react with Metal Carbonates And Metal Hydrogencarbonates to form Salt, carbon dioxide and Water. Metal Carbonate/Metal Hydrogen Carbonate + Acid → Salt + Carbon dioxide + Water.
  • Examples: (i) 2HCl + Na2CO3 = 2NaCl + CO2 + H2O

(ii) HCl + NaHCO3 = NaCl + CO2 + H2O

  • CO2 can be tested by passing it through lime water. It turns Lime Water Milky.

Ca(OH)2 + CO2 = CaCO3 +  H2O

  • When excess CO2 is passed, milkiness disappears.

CaCO3 + CO2 + H2O → Ca(HCO)3

  • Bases do not react with Metal Carbonates and Metal hydrogencarbonates. Base + Metal Hydrogen Carbonate → No Reaction.

The reaction of Acids and Bases with each other

  • Acids and bases react to form salt and water.                                                                                             Acid + Bases → Salt + CO2
  • Neutralisation Reaction: Reaction of acid with a base is called a neutralization reaction.       Example: HCl + NaOH → NaCl + H2O
  • Strong Acid + Weak Base → Acidic salt + H2O
  • Weak Acid + Strong Base → Base salt + H2O
  • Strong Acid + Strong Base → Neutral salt + H2O
  • Weak Acid + Weak Base → Neutral salt + H2O
The reaction of Metallic Oxides with Acid
Metallic oxides react with acids to give salts and water. Let us consider the reaction of copper oxide with dilute hydrochloric acid.
CuO + 2HCl → CuCl2 + H2O
After the reaction takes place the colour of the solution becomes blue-green due to the formation of copper (II) chloride and the copper oxide dissolves. This proves that metallic oxides are basic oxides.
CuO + HCl → CuCl2 + H2O

The reaction of Non-Metallic Oxides with Base

Non-metallic oxides are formed by the reaction of non-metals with oxygen. They react with a base to give salts and water. Let us consider the reaction of Calcium hydroxide (base) with carbon dioxide (non-metallic oxide) to produce salt and water.
Ca(OH)2  + CO2 → CaCO3 + H2O

Importance of pH in everyday life

Acid Bases and Salts

pH Scale

  • Our body works within the pH range of 7.0 to 7.8. The pH of saliva ranges from 6.5-7.5.
  • When the pH of rainwater is less than 5.6, it is called acid rain that lowers the pH of the river water and makes it difficult for marine creatures to survive.
  • The pH of surface water is 6-8.5 and that of groundwater is nearly 6.5-8.5
  • Plants require a specific pH range for their healthy growth.
  • The pH of tomato juice ranges from 4.1 to 4.6 whereas the pH of carrot juice is 6.4.
  • Our stomach produces hydrochloric acid during digestion of food causing no harm. But during indigestion, an excess amount of acid is produced causing pain and irritation.
  • Bacteria present in the mouth generates acids by decomposing the remaining sugar and food particles in the mouth that lowers the pH to 5.5 and corrodes calcium phosphate present in our teeth enamel.
  • Ant sting injects formic acid and nettle stings and injects methanoic acid causing pain and irritation. Use of a mild base like baking soda on the stung area can provide relief to some extent due to neutralization reaction between acid and base.

Chemical from Common Salt

  • Salts formed by the blend of hydrochloric acid and sodium hydroxide solution is called sodium chloride.
  • The salt we commonly consume. It is neutral.
  • This neutral common salt acts as preliminary raw material for extracting several other materials of daily use, like sodium hydroxide, baking soda, washing soda, bleaching powder etc.

Water of crystallisation

  • The fixed number of water molecules present in one formula unit of salt is called water of crystallisation.
  • For instance, there are five molecules of water in one formula unit of copper sulphate and hence the chemical formula for hydrated copper sulphate is CuSO4. 5H2
  • Gypsum has two molecules of water as the water of crystallisation and hence the chemical formula for hydrated gypsum stands out to be CaSO4.2H2
  • This gypsum on getting heated loses water molecules and becomes calcium sulphate hemihydrate (CaSO4.1/2 H2O). This is known as plaster of Paris.
  • Uses of Plaster of Paris are as follows:
  • Plaster for supporting fractured bones in their appropriate position.
  • When mixed with water, it again changes to gypsum giving a hard solid mass. The reaction is as follows: CaSO1/2 H2O → CaSO4.2H2O.
  • It is also used for making toys, materials for decoration and for making smooth surfaces.

 

SCIENCE Revision Notes

Chapter:01  Chemical Reaction & Equation
Chapter:02  Acid-Base & Salt
Chapter:03  Metals & Non Metals
Chapter:04  Carbon & its Components
Chapter:05  Periodic Classification of Elements
Chapter:06  Life Processes
Chapter:07  Control & Coordinates
Chapter:08  How do Organisms Reproduce
Chapter:09  Heredity & Evolution
Chapter:10  Light Reflection Refraction
Chapter:11  The Human Eye & the Colourful World
Chapter:12  Electricity
Chapter:13  Magnetic Effect of Electric Current
Chapter:14  Source Of Energy
Chapter:15  Our Environment
Chapter:16  Management of Natural Resource

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