Notes: Materials of Daily use | Science & Pedagogy Paper 2 for CTET & TET Exams - CTET & State TET PDF Download

The advancement of chemistry as a science has given us a wide range of materials that we use in our daily lives. Acids, bases, and salts are fundamental to the production of such materials. Soaps, polymers, and cements are a few examples of these materials, which have not only made human life easier but also led to unprecedented improvements in our lifestyle.

Acids

Acids are substances that have a sour taste and turn blue litmus paper red. They ionize in water to produce hydrogen ions (H⁺). Acids can be classified into organic acids (obtained from living sources) and mineral acids (obtained from non-living sources).

Properties of Acids

• Acids are conductors of electricity.
• Acids evolve hydrogen gas when reacting with active metals.
• Acids react with metal carbonates and bicarbonates to produce carbon dioxide gas.
• Acids react with bases to produce salts and water; this reaction is known as neutralization.
• Acids are corrosive in nature.

Classification of Acids

Class I: Based on Degree of Dissociation

• Strong acids: Completely dissociate even in concentrated solutions, e.g., HCl, HNO₃, H₂SO₄, HClO₄.
• Weak acids: Partially dissociate when dissolved in water, e.g., acetic acid (CH₃COOH), formic acid (HCOOH).

Class II: Based on Presence of Oxygen or Hydrogen

• Hydracids: Do not contain oxygen, include hydrochloric acid (HCl), hydrofluoric acid (HF).
• Oxyacids: Contain both oxygen and hydrogen, include sulfuric acid (H₂SO₄), nitric acid (HNO₃).

Sources and Uses of Some Important Acids

Acid Burns

When preparing dilute solutions of acids (e.g., H₂SO₄, HCl, HNO₃), it's crucial to add acid to water slowly with continuous stirring. Adding water to acid can produce significant heat, potentially causing the glass container to break and resulting in serious acid burns if the hot contents splash onto clothes or skin.

Aqua-regia

Aqua-regia is a mixture of hydrochloric acid and nitric acid in a ratio of 1:3. It is a powerful chemical reagent capable of dissolving even noble metals like gold and platinum.

Acid Rain

Rain that contains an excess of acids such as carbonic acid, sulfuric acid, and nitric acid is termed acid rain. This phenomenon occurs when CO₂, SO₂, and NO₂ dissolve in raindrops. Acid rain causes severe environmental pollution, damaging animal skins, plants and crops, and eroding buildings and bridges.

Acid-Containing Biomolecules

Important biomolecules in living systems are acids. DNA and RNA are nucleic acids, while proteins and fats consist of amino acids and fatty acids, respectively.

Bases

Bases have a bitter taste, a soapy touch, and turn red litmus paper blue. They dissociate in water to produce hydroxyl ions (OH^-). Not all bases have a bitter taste, and those that dissolve in water are called alkalies.

Properties of Bases

• Bases are conductors of electricity.
• They evolve hydrogen gas only with certain metals.
• Bases react with acids to form salt and water (neutralization reaction).
• Bases can be corrosive.

Sources and Uses of Some Important Bases

Lewis Acids and Bases

According to the Lewis concept, a base donates an electron pair to form a coordinate bond, and an acid accepts the electron pair. Lewis acids are electron deficient species (electrophiles) like AlCl₃, Co²⁺, Mg²⁺, etc. Lewis bases are electron rich species (nucleophiles) like H₂O, NH₃, OH^-, NO, CO^-, etc.

Limitations of Lewis Concept

• The strength of Lewis acids and bases depends on the type of reaction; they cannot be arranged in a consistent order of relative strength.
• The Lewis concept does not explain the behavior of protonic acids such as HNO₃, HCl, and H₂SO₄.
• Many acids act as catalysts due to their ability to release H⁺ ions, which Lewis acids do not.

Soaps and Detergents

Soaps are sodium or potassium salts of higher fatty acids, made by reacting fats or oils with sodium hydroxide through a process called saponification. The reaction produces soap and glycerol as a byproduct. Soap molecules have hydrophobic (water-repelling) and hydrophilic (water-attracting) ends, which help in cleaning by attaching to grease and dirt particles and dispersing them in water.

Detergents, made from petroleum hydrocarbons, also have hydrophobic and hydrophilic ends. They are effective in both soft and hard water.

Natural Fibres

Natural fibres are obtained from plant or animal sources:

• Cotton: Obtained from cotton plants grown in regions with black soil and warm climate like Gujarat. It is composed of cellulose.
• Jute: Obtained from the stem of jute plants grown in Bihar, West Bengal, and Assam. Fibres are separated by soaking the stems in water.
• Wool: Obtained from animals like sheep, goat, and yak. Shearing is done to remove the fleece, which is then washed and sorted. Wool is a protein fibre.
• Silk: Obtained from silkworms through the process of sericulture. Silk fibres are extracted from cocoons and used in textiles.

Synthetic Fibres

Synthetic fibres are man-made polymers with high molecular weight:

• Rayon: Derived from natural cellulose by chemical treatment. It has a silky appearance and is used in blends with cotton and wool.
• Nylon: The first fully synthetic fibre, made from coal, water, and air. It is strong, heat-resistant, and used in various applications from textiles to industrial products.
• Polyester: Made from ester units, it is durable, wrinkle-resistant, and used widely in textiles and PET bottles.
• Acrylic: Resembles wool and is used in sweaters, blankets, etc. It is cheaper and available in various colors.

Testing of Fibres

Plastics

Plastics are polymers with different arrangements, classified into:

• Thermoplastic: Soften on heating and can be reshaped, e.g., polythene, polystyrene, PVC.
• Thermosetting: Do not soften on heating, retain their shape permanently due to cross-linking, e.g., bakelite, melamine.

Properties of plastics:

• Non-reactive and corrosion-resistant.
• Lightweight, strong, and durable.
• Poor conductor of electricity and heat.
• Environmentally hazardous and causes pollution.

Important Plastics

• Polythene: Chemically inactive, water-resistant, tough, flexible, and strong. It can be molded into desired shapes.
• Polyvinyl Chloride (PVC): Tougher than polythene, a good insulator.
• Polystyrene: Very light, easily blown, and more moldable than polythene.
• Perspex: Extremely tough, lightweight, very transparent, and has high optical clarity.
• Teflon: Very tough, resistant to acids and bases, a poor conductor of heat. Also known as the best plastic.
• Bakelite: Hard and strong, fire-resistant, becomes brittle upon excessive heating.
• Melamine: Versatile, resistant to fires, can tolerate heat better than other plastics.

Plastics & Environmental Concerns

Plastics, like polythene bags, are difficult to dispose of and can remain undecomposed for hundreds of years. When burned, they produce poisonous fumes. Animals can suffer serious health issues if they ingest plastics. Hence, it is important to find biodegradable alternatives like vegetable-based materials, paper, wood, and cotton clothes.

Biodegradable materials can be decomposed by microorganisms like bacteria, whereas non-biodegradable materials like plastics and non-metals cannot.

Bleaching Agents

Drugs

A drug is a chemical substance that affects human metabolism and provides cure from ailments. Drugs are classified based on their therapeutic actions:

• Analgesics: Drugs that give relief from pain, e.g., Morphine, Heroin, Aspirin, etc.
• Antiseptics: Chemicals that check the growth of microorganisms without harming human tissues, e.g., Dettol, Bithinol, Tincture of Iodine, etc.
• Disinfectants: Chemicals that prevent the growth of microorganisms and are used on inanimate objects, e.g., Phenol solution, chlorine in aqueous solution, etc.
• Antibiotics: Inhibit the growth or destroy microorganisms by interfering with their metabolic processes, e.g., Penicillin.
• Antacids: Substances that neutralize excess stomach acid, e.g., Sodium hydrogen carbonate, Aluminium and Magnesium hydroxide.
• Tranquilizers: Chemicals used to treat stress and mental problems, also called anti-depressant drugs, e.g., Equanil, Serotonin, Chlorodiazepoxide.

There are many other important classes of drugs based on their action, such as anti-histamines, anti-microbials, anti-fertility drugs, antipyretics, etc.