Acids, Bases and Salts 🌡️

An acid is a chemical substance that, when dissolved in water, produces hydrogen ions, as the only positively charged ions. An acid can also be defined as a proton donor 🧪.

Note: Hydrogen ions give acids their characteristic properties, and all acids behave similarly because they contain hydrogen ions. ⚗️

Types of Acids

Mineral Acids

Mineral acids, also known as inorganic acids, are prepared from minerals obtained from the earth. These are generally strong acids 💪. Examples include:

• Hydrochloric acid (HCl) 🧪
• Nitric acid (HNO3) 💧
• Sulphuric acid (H2SO4) ⚗️
• Phosphoric acid (H3PO4) 🌱

Organic Acids

Organic acids are naturally occurring in living organisms and are prepared from organic sources like plants 🌿. These are generally weak acids. Examples include:

• Methanoic acid (HCOOH) 🍃
• Ethanoic acid (CH3COOH) 🥗
• Propanoic acid (C2H5COOH) 🍏
• Butanoic acid (C3H7COOH) 🍋

Ionization of Acids

Ionization is the process of forming ions. An ion is a charged particle. When acids dissolve in water, they produce hydrogen ions (H⁺) as the only positively charged ions. 💧

Examples of Ionization of Acids

• Hydrochloric acid (HCl): HCl(aq) → H⁺(aq) + Cl^-(aq)
• Nitric acid (HNO₃): HNO₃(aq) → H⁺(aq) + NO₃^-(aq)
• Ethanoic acid (CH₃COOH): CH₃COOH(aq) → H⁺(aq) + CH₃COO^-(aq)

Strength of Acids

The strength of an acid is a measure of its ability to produce hydrogen ions. Acids are categorized as weak or strong based on their ionization level. ⚖️

Weak Acids

A weak acid partially ionizes when dissolved in water. They have reversible ionization. Examples include:

• Ethanoic acid 🍏
• Carbonic acid 💧

Strong Acids

A strong acid completely ionizes in water. Examples include:

• Hydrochloric acid (HCl) 🧪
• Nitric acid (HNO₃) 💧
• Sulphuric acid (H₂SO₄) ⚗️

Definition: Basicity of an acid (also called protocity) is the number of moles of hydrogen ions (H⁺) produced from one mole of an acid. 🔍

Monobasic Acids

A monobasic acid produces one hydrogen ion. 🔹

• Hydrochloric acid (HCl) 🧪
• Ethanoic acid (CH₃COOH) 🍏

Dibasic Acids

A dibasic acid produces two hydrogen ions. Example:

• Carbonic acid (H₂CO₃) 💧
• Sulphuric acid (H₂SO₄) ⚗️

Tribasic Acids

A tribasic acid produces three hydrogen ions. Example:

• Phosphoric acid (H₃PO₄) 🌱

Physical Properties of Acids

• Acids have a pH less than 7. 📉
• Acids turn blue litmus paper red. 🔴
• Acids have a sour taste. 😋

Chemical Properties of Acids

Acids react with metals, bases, alkalis, and carbonates. Below are some examples:

Reaction with Reactive Metals

Acids react with metals to form a salt and hydrogen gas:

• 2Na(s) + 2HCl(aq) → 2NaCl(aq) + H₂(g) ⚗️
• Ca(s) + H₂SO₄(aq) → CaSO₄(aq) + H₂(g) ⚗️

Note: Metals below hydrogen in the reactivity series cannot react with acids. 🚫

Reaction with Bases (Neutralization)

Acids react with bases or alkalis to form a salt and water:

• NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l) ⚖️
• CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l) ⚖️

• Benzoic acid: Used as a food preservative. 🍽️
• Carbonic acid: Carbonated drinks. 🥤
• Ethanoic acid: Main component of vinegar, used in pickling. 🥒
• Hydrochloric acid: Used in metal cleaning, leather processing, and pool maintenance. 🧼
• Nitric acid: Production of fertilizers, explosives, and metal purification. 💣
• Sulphuric acid: Used in detergents, fertilizers, and car batteries. 🔋

Bases

A base is a substance that reacts with an acid to form a salt and water. A soluble base is called an alkali, and alkalis produce hydroxide ions (OH^-) in water. 💧

Examples of Alkalis

• Sodium hydroxide (NaOH): Known as caustic soda. 🧼
• Potassium hydroxide (KOH): Known as caustic potash. 🌾
• Ammonium hydroxide (NH₄OH): Also called aqueous ammonia. 💨

Ionization of Alkalis

When alkalis dissolve in water, they produce hydroxide ions (OH^-) as the only negatively charged ions. 💧

• NaOH(aq) → Na⁺(aq) + OH^-(aq)
• NH₄OH(aq) → NH₄⁺(aq) + OH^-(aq)

Strength of Alkalis

The strength of an alkali measures its ability to produce hydroxide ions. Alkalis can be weak or strong. ⚖️

Weak Alkalis

Partially ionize in water. Example:

• Ammonium hydroxide (NH₄OH) 💧

Strong Alkalis

Completely ionize in water. Examples include:

• Sodium hydroxide (NaOH) 🧼
• Potassium hydroxide (KOH) 🌾

• Ammonia: Used in fertilizers and nitric acid production. 🌱
• Calcium hydroxide: Used in cement production and soil neutralization. 🏗️
• Sodium hydroxide: Manufacturing of soaps and detergents. 🧼

The pH Scale

Definition: The pH scale measures the degree of acidity or alkalinity of a substance and ranges from 0 to 14. 📊

• pH values from 0 to 7 indicate an acidic medium. 🔴
• pH value of 7 indicates a neutral medium (e.g., water). ⚪
• pH values from 7 to 14 indicate an alkaline medium. 🟢

The ion responsible for acidity is the hydrogen ion (H⁺), while the hydroxide ion (OH^-) is responsible for alkalinity. 💧

pH measurements are important across various fields, including industry, agriculture, pharmacy, and medicine. 🌍

Control of pH in Agriculture

Plants have specific pH requirements for optimal growth. For example, some plants thrive in slightly acidic soils (pH ~6.5), while others prefer alkaline soils (pH ~7.5). If the soil becomes too acidic due to acid rain, it can be treated with slaked lime (calcium hydroxide) to neutralize the acidity. 🌱

Acid Rain

Acid rain is formed when gaseous acidic oxides dissolve in atmospheric rainwater, resulting in acidic compounds like nitric acid, carbonic acid, and sulfuric acid. Acid rain causes environmental pollution, leading to acidic soils, damaged crops, and vegetation loss. 🌧️

Examples of Acid Formation

• Nitric Acid: Formed when nitrogen dioxide dissolves in rainwater (NO₂ + H₂O → HNO₃) 🌧️
• Carbonic Acid: Formed when carbon dioxide dissolves in rainwater (CO₂ + H₂O → H₂CO₃) 🌧️
• Sulfuric Acid: Formed when sulfur trioxide dissolves in rainwater (SO₃ + H₂O → H₂SO₄) 🌧️

Indicators

An indicator is a chemical that shows different colors in acidic and alkaline solutions. Common indicators include: 🎨

1. Describe how acid rain is formed and suggest ways to prevent it. 🌧️

2. What pH value indicates a neutral solution? ⚖️

Oxides

Definition: An oxide is a compound formed when oxygen combines with another element. Oxides are categorized as acidic, basic, amphoteric, or neutral. 🌬️

Acidic Oxides

These are oxides of non-metals that react with water to form acids or with alkalis to form salts. ⚗️

• Examples: CO₂, NO₂, SO₂, SO₃

Basic Oxides

These are oxides of metals that react with acids to form salts and water. ⚗️

• Examples: Na₂O, MgO, CaO

Amphoteric Oxides

These oxides can act as both acidic and basic, reacting with both acids and alkalis to form salts and water. ⚖️

• Examples: ZnO, Al₂O₃

Neutral Oxides

These oxides do not show acidic or basic properties and do not react with acids or bases. ⚪

• Examples: CO, NO

Salts

Definition: A salt is formed when the hydrogen ions in an acid are replaced by metal or ammonium ions. Salts are classified into normal salts, acid salts, and basic salts. 🧂

Normal Salts

Formed when all hydrogen ions in an acid are replaced by metal ions. 🧂

• Examples: NaCl, CaSO₄, CuSO₄

Acid Salts

Formed when only part of the hydrogen ions in an acid are replaced by metal ions. 🧂

• Examples: NaHSO₄, Ca(HCO₃)₂

Solubility of Salts

Salts vary in solubility based on their types. For instance:

• All nitrates are soluble. 💧
• Chlorides are generally soluble, except AgCl and PbCl₂. 💧
• Sulphates are soluble, except BaSO₄ and PbSO₄. 💧

Salts are prepared using methods like neutralization, displacement, synthesis, and precipitation. The chosen method depends on the salt’s solubility and how it can be isolated from other products. 🧪

Neutralization

Neutralization involves the reaction between an acid and a base to form a salt and water. ⚖️

• Example: NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)

Displacement

In displacement reactions, a more reactive metal displaces a less reactive metal from its compound. ⚙️

• Example: Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

Precipitation

Precipitation occurs when two soluble salts react to form an insoluble salt. 💧

• Example: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

Hydrated and Anhydrous Salts

Hydrated salts contain water molecules within their crystal lattice, while anhydrous salts lack these water molecules. 💧

Example: When blue copper sulfate crystals (CuSO₄•5H₂O) are heated, they lose water, turning into anhydrous copper sulfate (CuSO₄). 🔥

Efflorescence

Efflorescence is the loss of water of crystallization to the atmosphere, as seen in sodium carbonate crystals. 🌬️

Deliquescence

Deliquescent salts absorb water from the atmosphere and form a solution. Calcium chloride is a deliquescent salt. 💧

Hygroscopic Substances

Hygroscopic substances absorb water from the air but do not change state. An example is anhydrous cobalt chloride, which changes from blue to pink upon absorbing water. 🌈

Oxidation and Reduction

Oxidation and reduction can be defined in terms of oxygen, hydrogen, electrons, and oxidation number. 🔄

Oxidation

• In terms of oxygen: Oxidation is the addition of oxygen to a substance. 🌬️
• In terms of hydrogen: Oxidation is the removal of hydrogen from a substance. 🔥
• In terms of electrons: Oxidation is the loss of electrons from a substance. ⚡
• In terms of oxidation number: Oxidation is an increase in oxidation number. 📈

Examples of Oxidation

• Oxidation of Magnesium: 2Mg(s) + O₂(g) → 2MgO(s) 🔥
• Oxidation of Copper: Cu → Cu²⁺ + 2e^- ⚡

Reduction

• In terms of oxygen: Reduction is the removal of oxygen from a substance. 🌬️
• In terms of hydrogen: Reduction is the addition of hydrogen to a substance. 🔥
• In terms of electrons: Reduction is the gain of electrons by a substance. ⚡
• In terms of oxidation number: Reduction is a decrease in oxidation number. 📉

Examples of Reduction

• Reduction of Carbon Dioxide: CO₂(g) + C(s) → 2CO(g) 🔥
• Reduction of Copper Ions: Cu²⁺ + 2e^- → Cu(s) ⚡

Oxidizing and Reducing Agents

An oxidizing agent is a substance that brings about oxidation by accepting electrons and is itself reduced. Common oxidizing agents include oxygen, chlorine, and potassium permanganate. 🌬️

A reducing agent is a substance that brings about reduction by donating electrons and is itself oxidized. Common reducing agents include hydrogen, carbon, and ammonia. 🔥

Redox Reactions

Redox reactions involve simultaneous oxidation and reduction. When one substance is oxidized, another is reduced. 🔄

Examples of Redox Reactions

• Fe₂O₃(s) + 2Al(s) → Al₂O₃(s) + 2Fe(s) 🔄
• Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s) 🔄

1. Determine if the following reactions are examples of oxidation or reduction: 🔄

• Al³⁺ + 3e^- → Al
• Cl₂ + 2e^- → 2Cl^-

2. Identify which substance is oxidized and which is reduced in the following reactions: 🔄

• CO₂ + C → 2CO
• 2FeO₃ + 2Al → Al₂O₃ + 2Fe

Tests for Gases

Various tests can identify gases based on color, odor, and reactions with specific indicators. 🔍