Chapter 2 Class 10 – Acids, Bases and Salts
Acids, Bases, and Salts in Daily Life
Acids, bases, and salts play a crucial role in our daily life and in various industrial applications. Acids are commonly used in food preservation (like vinegar), in cleaning products, and for medicinal purposes (e.g., stomach acids). Bases are often found in household cleaning products, soaps, and detergents, where they neutralize acids. Salts, which are the products of acid-base reactions, have various uses such as in cooking, water treatment, and in the preparation of other chemicals like baking soda and washing soda.
Point-wise:
- Acids: Found in food (vinegar), cleaning products, and medicines.
- Bases: Present in soaps, detergents, and cleaning agents.
- Salts: Used in cooking, water softening, and chemical production.
Indicators of Acids and Bases
Indicators are substances that change color when exposed to an acid or a base. Some common acid-base indicators include litmus paper, phenolphthalein, and methyl orange. Litmus paper turns red in acids and blue in bases. These indicators are widely used to determine the acidity or alkalinity of a solution and are essential in both laboratory experiments and industrial processes.
Point-wise:
- Litmus Paper: Turns red in acids and blue in bases.
- Phenolphthalein: Colorless in acids and pink in bases.
- Methyl Orange: Red in acids and yellow in bases.
Acids
Acids are substances that release hydrogen ions (H⁺) when dissolved in water. They are generally characterized by their sour taste, ability to turn blue litmus paper red, and their reactivity with metals to release hydrogen gas. Acids are further classified into strong and weak acids based on their ionization in water. Strong acids, such as hydrochloric acid (HCl), completely dissociate in water, while weak acids, like acetic acid (CH₃COOH), partially dissociate.
Point-wise:
- Definition: Release H⁺ ions in water.
- Characteristics: Sour taste, turns blue litmus paper red, reacts with metals.
- Examples: Hydrochloric acid (HCl), Sulfuric acid (H₂SO₄).
- Strong Acids: HCl, HNO₃.
- Weak Acids: CH₃COOH (acetic acid).
Classification of Acids
Acids can be classified into two main categories based on their chemical behavior: organic acids and inorganic acids. Organic acids are typically derived from plant or animal sources and contain carbon in their molecular structure (e.g., acetic acid). Inorganic acids, on the other hand, do not contain carbon and are usually derived from mineral sources (e.g., sulfuric acid).
Point-wise:
- Organic Acids: Contain carbon in their structure.
- Example: Acetic acid (CH₃COOH).
- Inorganic Acids: Do not contain carbon.
- Example: Sulfuric acid (H₂SO₄).
Bases
Bases are substances that release hydroxide ions (OH⁻) when dissolved in water. Bases have a bitter taste, slippery texture, and can turn red litmus paper blue. Strong bases, like sodium hydroxide (NaOH), completely dissociate in water, whereas weak bases, like ammonia (NH₃), only partially dissociate. Bases are commonly used in soaps, detergents, and as neutralizing agents for acids.
Point-wise:
- Definition: Release OH⁻ ions in water.
- Characteristics: Bitter taste, slippery texture, turns red litmus paper blue.
- Examples: Sodium hydroxide (NaOH), Calcium hydroxide (Ca(OH)₂).
- Strong Bases: NaOH, KOH.
- Weak Bases: Ammonia (NH₃).
Classification of Bases
Bases can be classified into strong and weak bases. Strong bases like NaOH dissociate completely in water, releasing a large number of OH⁻ ions. On the other hand, weak bases, such as ammonia (NH₃), do not dissociate completely and release fewer hydroxide ions. The strength of a base determines its reactivity with acids and its ability to neutralize them.
Point-wise:
- Strong Bases: Completely dissociate in water.
- Example: Sodium hydroxide (NaOH).
- Weak Bases: Partially dissociate in water.
- Example: Ammonia (NH₃).
Difference Between Acids and Bases
The fundamental difference between acids and bases lies in the ions they release in water. Acids release H⁺ ions, while bases release OH⁻ ions. Additionally, acids have a sour taste, turn litmus paper red, and are corrosive in nature, while bases have a bitter taste, turn litmus paper blue, and feel slippery to the touch. Acids are commonly used for digestion and cleaning, while bases are used in soaps and neutralizing agents.
Point-wise:
- Acids:
- Release H⁺ ions.
- Taste sour.
- Turn blue litmus paper red.
- Example: HCl, H₂SO₄.
- Bases:
- Release OH⁻ ions.
- Taste bitter.
- Turn red litmus paper blue.
- Example: NaOH, Ca(OH)₂.
Reactions of Acids and Bases
Acids and bases react with a variety of substances, forming different products. When an acid reacts with a metal, hydrogen gas is released, and a salt is formed. When acids react with bases, a neutralization reaction occurs, forming a salt and water. Acids also react with metal carbonates to release carbon dioxide gas, forming a salt and water.
Point-wise:
- Acid + Metal: Forms a salt and H₂ gas.
- Example: HCl + Zn → ZnCl₂ + H₂.
- Acid + Base: Forms a salt and water.
- Example: HCl + NaOH → NaCl + H₂O.
- Acid + Metal Carbonate: Forms a salt, CO₂, and H₂O.
- Example: HCl + Na₂CO₃ → NaCl + CO₂ + H₂O.
Neutralization Reaction
A neutralization reaction occurs when an acid reacts with a base to produce a salt and water. This reaction is essential in many real-world applications, such as in antacids that neutralize stomach acid or in soil treatment to neutralize acidic or basic soil conditions. The general equation for a neutralization reaction is:
Acid + Base → Salt + Water
Point-wise:
- Neutralization: Acid + Base → Salt + Water.
- Example: HCl + NaOH → NaCl + H₂O.
Strength of Acids and Bases
The strength of an acid or a base depends on the extent of dissociation in water. Strong acids (like HCl) dissociate completely in water, releasing a large number of H⁺ ions. Similarly, strong bases (like NaOH) dissociate completely to release OH⁻ ions. Weak acids and weak bases dissociate partially in water. The strength of acids and bases can be measured using the pH scale.
Point-wise:
- Strong Acids: Completely dissociate in water.
- Example: HCl, H₂SO₄.
- Weak Acids: Partially dissociate in water.
- Example: CH₃COOH.
- Strong Bases: Completely dissociate in water.
- Example: NaOH, KOH.
- Weak Bases: Partially dissociate in water.
- Example: NH₃.
Importance of pH in Everyday Life
The pH scale plays a critical role in various aspects of life and science. The pH of substances can affect biological processes, chemical reactions, and industrial processes. For example, the pH of soil influences plant growth, and the pH of the human stomach affects digestion. The pH scale also helps in water treatment, food preservation, and medicine. A pH of 7 is neutral, while values below 7 are acidic, and above 7 are basic.
Point-wise:
- pH Scale: Ranges from 0 to 14.
- pH 7: Neutral (e.g., water).
- pH < 7: Acidic.
- pH > 7: Basic/Alkaline.
- Importance:
- Soil pH affects plant growth.
- Stomach pH aids digestion.
- Water pH affects water quality.
Salts
Salts are ionic compounds formed by the reaction between acids and bases. When acids and bases neutralize each other, they form salts and water. Some salts, like sodium chloride (NaCl), are common table salts, while others are used in various industrial processes. Salts like baking soda (NaHCO₃) and washing soda (Na₂CO₃·10H₂O) have diverse applications in daily life and industries.
Point-wise:
- Salts: Formed by the reaction of acids and bases.
- Example: NaCl (table salt).
- Uses: In cooking, water softening, cleaning, and chemical production.
Chemicals from Common Salt
Common salt, or sodium chloride (NaCl), is used to produce a variety of useful chemicals. Through the process of electrolysis of sodium chloride (brine), products like sodium hydroxide (NaOH), chlorine gas (Cl₂), and hydrogen gas (H₂) are produced. Sodium hydroxide is used in soap making and paper production, while chlorine gas is used to produce bleaching powder and disinfectants.
Point-wise:
- Sodium Chloride (NaCl): Source of various chemicals.
- Sodium Hydroxide (NaOH): Used in soap making.
- Chlorine Gas (Cl₂): Used to make bleaching powder.