Comprehensive Study Notes: Acids, Bases, and Salts

Acids, Bases, and Salts

Introduction

This chapter explores the classification, properties, and uses of acids, bases, and salts, which are fundamental concepts in general chemistry. Understanding these substances is essential for grasping chemical reactions, laboratory techniques, and real-world applications.

• Acids are substances that release hydrogen ions (H+) in aqueous solutions.

• Bases are substances that release hydroxide ions (OH-) in aqueous solutions.

• Salts are ionic compounds formed from the neutralization reaction between acids and bases.

Classification of Acids

Based on Source of Origin

• Organic acids: Derived from living organisms (e.g., citric acid, acetic acid).

• Mineral acids (Inorganic acids): Derived from minerals (e.g., hydrochloric acid, sulfuric acid).

Organic acids	Source
Citric acid	Citrus fruits
Acetic acid	Vinegar
Tartaric acid	Tamarind

Mineral acids	Chemical formula
Hydrochloric acid	HCl
Sulfuric acid	H2SO4
Nitric acid	HNO3

Strength of Acids and Bases

• Strong acids: Completely ionize in water (e.g., HCl, HNO3).

• Weak acids: Partially ionize in water (e.g., CH3COOH).

• Strong bases: Completely dissociate in water (e.g., NaOH, KOH).

• Weak bases: Partially dissociate in water (e.g., NH4OH).

Example equations:

• Strong acid: $\mathrm{HCl} \rightarrow \mathrm{H^+} + \mathrm{Cl^-}$

• Weak acid: $\mathrm{CH_3COOH} \rightleftharpoons \mathrm{CH_3COO^-} + \mathrm{H^+}$

• Strong base: $\mathrm{NaOH} \rightarrow \mathrm{Na^+} + \mathrm{OH^-}$

• Weak base: $\mathrm{NH_4OH} \rightleftharpoons \mathrm{NH_4^+} + \mathrm{OH^-}$

Methods of Preparation

Acids

• By direct combination of elements: e.g., $\mathrm{H_2} + \mathrm{Cl_2} \rightarrow 2\mathrm{HCl}$

• From non-metals: e.g., $\mathrm{S} + \mathrm{O_2} \rightarrow \mathrm{SO_2}$, then $\mathrm{SO_2} + \mathrm{H_2O} \rightarrow \mathrm{H_2SO_3}$

Bases

• From metals: e.g., $2\mathrm{Na} + 2\mathrm{H_2O} \rightarrow 2\mathrm{NaOH} + \mathrm{H_2}$

• Preparation of slaked lime: $\mathrm{CaO} + \mathrm{H_2O} \rightarrow \mathrm{Ca(OH)_2}$

Physical Properties of Acids and Bases

Property	Acids	Bases
Taste	Sour	Bitter
Feel	Corrosive	Soapy
Solubility	Soluble in water	Some bases insoluble in water

Chemical Properties

Acids

• React with metals to produce hydrogen gas.

• React with carbonates to produce carbon dioxide.

• Neutralize bases to form salt and water.

Bases

• React with acids to form salt and water.

• React with ammonium salts to release ammonia gas.

Indicators

Indicators are substances that change color in the presence of acids or bases.

Indicator	Color in Acid	Color in Base
Litmus	Red	Blue
Methyl orange	Red	Yellow
Phenolphthalein	Colorless	Pink

Types of Salts

• Normal salts: All H+ ions replaced by metal ions (e.g., NaCl).

• Acidic salts: Only some H+ ions replaced (e.g., NaHSO4).

• Basic salts: Contain OH- ions (e.g., Mg(OH)Cl).

• Double salts: Contain two different cations (e.g., alum).

• Mixed salts: Contain more than one acid or base radical (e.g., CaNaPO4).

• Complex salts: Contain complex ions (e.g., K4[Fe(CN)6]).

Properties of Salts

• Salts are solid at room temperature.

• Some salts are hydrated (contain water of crystallization).

• Salts may be neutral, acidic, or basic depending on their parent acid and base.

Uses of Acids, Bases, and Salts

Name	Use
Hydrochloric acid	Cleaning metals
Sulfuric acid	Manufacture of fertilizers
Sodium hydroxide	Soap making
Calcium carbonate	Manufacture of cement

Points to Remember

• Strength of acids and bases depends on the extent of ionization.

• Acids react with bases to form salts and water (neutralization reaction).

• Indicators help identify acids and bases.

• Salts can be classified as normal, acidic, basic, double, mixed, or complex.

Key Equations

• Neutralization: $\mathrm{Acid} + \mathrm{Base} \rightarrow \mathrm{Salt} + \mathrm{Water}$

• Example: $\mathrm{HCl} + \mathrm{NaOH} \rightarrow \mathrm{NaCl} + \mathrm{H_2O}$

Additional info:

• The pH scale measures the acidity or basicity of a solution, ranging from 0 (strongly acidic) to 14 (strongly basic), with 7 being neutral.

• Acids have pH less than 7, bases have pH greater than 7.