CBSE Class 10 Science Chapter 2 - Acid, Bases and Salts Revision Notes

Class Notes of Ch 2 : Acid, Bases and Salts
Class 10th Science

Acid, Bases and Salts

      Topics:

• Introduction
• Properties of Acids
• Properties of Bases
• Types of Indicators and its Properties
• Reaction of Acids and Bases with Metals
• Reaction of Acids with Carbonates and Metal Hydrogencarbonates
• Reaction of Acids and Bases with each other
• Reaction of Metallic Oxide with Acid
• Reaction of Non-metallic Oxide with Bases
• Similarities between all Acids and Bases solutions
• Importance of pH in everyday life
• Chemical from Common Salt
• Water of Crystallization

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 colour of blue litmus to red. 

(iv) Acids conduct electricity current.

(v) It reacts with metals produces salt and hydrogen gas. 

Bases: 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 color of red litmus into blue. 

(iv) Bases conduct electricity current. 

(v) It also reacts with metals gives salt and hydrogen gas.

Types of Indicators and its Properties

Indicators: Substance which change their color/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, phenolpthalein.

(iii) Olfactory Indicators: These substances have different odour in acid and base.

Reaction of Acids & Bases with Metals

Reaction of Acids with Metal

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

           Acid + Metal → Hydrogen Gas

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

           2HCl + Zn = ZnCl₂ + H₂

Reaction of Base with Metal

• Bases react with metal to evolve hydrogen gas. Also, note that all metal do 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 burning candle near gas bubbles, it burst with pop sound.

Reaction of Acids with Metal Carbonates and Metal Hydrogencarbonates

• Acids reacts 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

• CO_{2 can be tested by passing it through lime water. It turns Lime Water Milky.}

                        Ca(OH)2 + CO_{2 = CaCO}3 +  H₂O

• When excess CO_{2 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. 

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 base is called as 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

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 color 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

Reaction of Non-Metallic Oxides with Base

Non-metallic oxides are formed by the reaction of non-metals with oxygen. They react with 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  +} CO_{2 →} CaCO3 + H₂O

Importance of pH in everyday life

• Our body works within the pH range of 7.0 to 7.8. The pH of saliva ranges from 6.5-7.5.
• When pH of rain water 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 ground water is nearly 6.5-8.5
• Plants require a specific pH range for their healthy growth.
• 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 a 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 a 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 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: CaSO4  1/2 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  Heridity & 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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