Chapter 2: Acids, Bases, and Salts

Introduction

 In this chapter, we’ll explore the fascinating world of acids, bases, and salts, which are fundamental chemistry concepts.

Acids are substances that release hydrogen ions (H+) when dissolved in water. They typically have a sour taste and can turn blue litmus paper red. Common examples include citric acid in lemons and acetic acid in vinegar.

Bases, on the other hand, are substances that release hydroxide ions (OH-) in water. They usually have a bitter taste and feel slippery to the touch, capable of turning red litmus paper blue. Household cleaners such as ammonia and baking soda are everyday examples of bases.

Salts are the products of reactions between acids and bases, characterized by their crystalline nature and varying degrees of solubility in water. Table salt (sodium chloride) is perhaps the most well-known example. Salts can also form during metal-acid /non metal – base reactions and have extensive uses in daily life, from food seasoning to manufacturing processes. Understanding these properties is essential not only for your academic knowledge but also because they apply directly to numerous real-world situations.

Throughout this chapter, students will delve into the various properties and behaviors of acids, bases, and salts. You will learn about their unique characteristics, how they interact with each other, and their countless applications in everyday life. Additionally, the chapter covers the pH scale, indicators to identify acidic and basic solutions, and the types of salts formed from different reactions. By the end of this chapter, you will have a comprehensive understanding of these vital chemical compounds and their roles in our world.

1. UNDERSTANDING THE CHEMICAL PROPERTIES OF ACID BASE AND SALTS (FEW KEY TERMS)

• Litmus paper:- Litmus paper is made by soaking filter paper in a solution of litmus dye, then drying it. The dye is a mixture of several different dyes extracted from lichen plant. it is a natural indicator used to determine whether a solution is acidic or basic (alkaline). It comes in two forms: red litmus paper and blue litmus paper.

• FUNCTIONALITY OF LITMUS PAPER

RED LITMUS

• • ACID     NO CHANGE
  • BASE      CHANGES TO BLUE COLOUR

 BLUE LITMUS

•   CHANGES TO RED COLOUR
• NO CHANGE

(In neutral Solution litmus paper changes to purple)

Acids

All those Substances that taste sour, turn blue litmus red, and release H⁺ ions in water all called acid. Following are the characteristics of acid

• Sour in taste
• Conduct electricity in aqueous solution ( because of presence of H+ ions)
• React with metals to produce hydrogen gas
• Examples: Hydrochloric acid (HCl), Sulfuric acid (H₂SO₄), Acetic acid (CH₃COOH)

Types of acid : Acids are divided into two types on the basis of their occurrence i.e., Natural acids and Mineral acids. And on the basis of power they are of two types I.e., Concentric and dilute acid

• Natural acid:- Acids which are obtained from natural sources are called Natural Acids or Organic Acids. They are generally weak and of high ph value as compared to mineral acid
  Examples:
  Methanoic acid (HCOOH)
  Oxalic acid (C2H2O4) etc.
• Mineral acid: – Acids that are prepared from minerals are known as Mineral Acids, Inorganic acids, man-made acids or synthetic acids. Following are the few examples,
• Hydrochloric acid (HCl)
• Sulphuric acid (H2SO4)
• Nitric acid (HNO3) etc.

Concentric and dilute acids: – All those acids whose ph. value is low is termed as concentric acid and vice versa dilute acid. Adding concentric acids in water make it dilute.

Bases

All those substances that taste bitter, feel slippery, turn red litmus blue, and release OH⁻ ions in water are called base. All bases are not soluble in water, those soluble in water are called alkali base. following are the characteristics of bases

• Bitter taste
• Slippery feel
• Conduct electricity in aqueous solution
• Examples: Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Calcium hydroxide [Ca(OH)₂]

Types of bases

• Water soluble (Alkali) these are powerful bases
• Water insoluble (Non alkali) These are less powerful

 Dilution of acid and base: – The concentration of H+ ions in an acid and -OH ion in a base, per unit volume, shows the concentration of acid or base and its power.

Dilution involves adding acid or base to water, decreasing the concentration of H⁺ or OH⁻ ions. This process is exothermic, so acid or base must be added to water, not the reverse. Adding water to concentrated acid or base can release excessive heat, causing dangerous splashing, as these substances are highly corrosive.

Salts

Formed when acids react with bases, neutralizing each other this reaction is also known as neutralization reaction. It is also formed during metal-acid reaction and non metal-base reaction

Salts are mostly crystalline solids and can be transparent or opaque. They generally dissolve in water, conduct electricity in molten form, and can have various tastes like salty, sour, or sweet. Neutral salts are odorless and can be either colorless or colored. Remember not all the salts are edible. Salts with the same acidic or basic radicals belong to the same family, e.g., sodium chloride and calcium chloride are in the chloride family, while calcium chloride and calcium sulfate are in the calcium family.

2. Indicators

Indicators are substances used to detect or measure specific properties of a material. In the context of acids and bases, certain indicators are used to identify the presence of these substances. They undergo a distinct change in color or smell when exposed to an acid or a base, making them useful tools in chemical analysis.

Types of Indicators

1. Natural Indicators: found naturally used to test presence of acid/base
   • Litmus: Extracted from lichens. They are generally are of two types 1. Blue litmus 2. Red litmus. Blue litmus turns red in acid, red litmus turns blue in base.
   • Turmeric: Turns reddish-brown in base, no change in acid.
   • Red Cabbage Juice: Turns red in acid, green in base.
2. Olfactory Indicators: those substances which changes its odor in presence of acid/base is known as olfactory indicator
   • Onion: Loses smell in base, no change in acid.
   • Vanilla: Smell vanishes in base, no change in acid.
3. Synthetic Indicators: indicators which are prepared in labs to test acidity/basicity of any substance
   • Phenolphthalein: Colorless in acid, pink in base.
   • Methyl Orange: Red in acid, yellow in base.

UNIVERSAL INDICATOR

 A universal indicator determines both the acidic or basic nature and the strength of a solution, unlike litmus paper, phenolphthalein, or methyl orange, which only indicate acidity or basicity. It displays a range of colors corresponding to pH values from 1 to 14 and is available as strips or in solution. Made from a mix of indicators like phenolphthalein, methyl red, and bromothymol blue, it comes with a color chart to match pH values accurately.

 pH Scale

 pH stands for “potential of hydrogen. It is an instrument used to measure acidity or basicity of any thing

pH paper is a type of universal indicator. It is treated with a combination of different indicators that change colour based on the pH level of a solution, providing an estimate of the solution’s acidity or basicity across the pH scale from 0 to 14.

• Scale ranges from 0 to 14:
  • pH < 7: Acidic
  • pH = 7: Neutral
  • pH > 7: Basic

Important Ph value

• Human body (blood): pH 7.35–7.45 (slightly alkaline)
• Stomach acid: pH 1.5–3.5 (highly acidic for digestion)
• Urine: pH 4.5–8 (varies depending on diet and health)
• Soil: pH 6–7.5 is generally considered ideal for most plants, though different plants prefer different levels.
• Tooth decay: Enamel starts to demineralize at a pH below 5.5 (acidic environment).

 Common Salt and Various Salts Obtained from It 

Common Salt (Sodium Chloride): Sodium chloride (NaCl) is also known as Common or Table Salt. It is formed after the reaction between sodium hydroxide and hydrochloric acid. It is a neutral salt. The pH value of sodium chloride is about 7. Sodium chloride is not just used to enhance the taste of food but also used in the manufacturing of many chemicals.

Salts Obtained from Common Salt

Various salts are derived from common salt through different chemical processes. Some of the most important salts are:

1. Sodium Hydroxide (NaOH) – Caustic Soda

Preparation: Sodium hydroxide is produced by the Chlor-Alkali process, where brine (a concentrated solution of NaCl) is electrolyzed.

Equation

2NaCl(aq)+2H2​O(l)→2NaOH(aq)+Cl2​(g)+H2​(g)

    Uses:

• Soap and detergent manufacturing
• Paper production
• Textile industry

2. Bleaching Powder (CaOCl₂)

• Preparation: Bleaching powder is produced by reacting chlorine (obtained in the chlor-alkali process) with dry slaked lime [Ca(OH)₂].
• Equation: Ca(OH)2​+Cl2​→CaOCl2​+H2​O
• Uses:
  • Disinfecting drinking water
  • Bleaching fabrics and paper
  • Cleaning and sanitizing surfaces

3. Baking Soda (Sodium Bicarbonate – NaHCO₃)

• Preparation: Baking soda is produced by passing carbon dioxide gas through a concentrated solution of sodium carbonate (Na₂CO₃).

• Equation: Na2​CO3​+CO2​+H2​O→2NaHCO3

Uses:

• As a leavening agent in baking
• As an antacid to relieve indigestion
• In fire extinguishers

4. Washing Soda (Sodium Carbonate – Na₂CO₃·10H₂O)

• Preparation: Washing soda is obtained by heating sodium bicarbonate, which decomposes into sodium carbonate. The sodium carbonate is then crystallized from a water solution to form washing soda.
• Equation

2NaHCO3 →​heat​ →Na2​CO3​+H2​O+CO2​

Uses:

• As a cleaning agent for domestic purposes
• In glass, soap, and paper manufacturing
• To soften hard water

5. Plaster of Paris (Calcium Sulphate Hemihydrate – CaSO₄·½H₂O)

Preparation: Plaster of Paris is obtained by heating gypsum (CaSO₄·2H₂O) at around 100°C. It loses water molecules and forms calcium sulfate hemihydrate.

 Equation:

CaSO4​⋅2H2​O →heat​→CaSO4​⋅½H2​O+1.5H2​O

 Uses:

• In making sculptures, casts, and moulds
• In construction (for plastering walls and ceilings)
• In orthopaedic casts for fractured bones

6. Sodium Carbonate (Na₂CO₃) – Soda Ash

Preparation: It is obtained from sodium chloride by the Solvay process, which involves the reaction of brine with ammonia and carbon dioxide.

Equation:

• NaCl+NH3​+CO2​+H2​O→NaHCO3​+NH4​Cl

Sodium bicarbonate is then heated to form sodium carbonate.

Uses:

• In the manufacturing of glass
• As a water softener in laundering
• In the production of chemicals

Reactions Involving Acids and Bases

Important Tables

Table: Indicators and Their Colour Changes