General Awareness
Chemistry Guide & Practice
Learn chemical formulas, types of reactions, pH scale, common compounds and their uses for SSC, Banking and Defence exam GK sections. Explore dynamic solver blueprints, master fundamental equations, examine step-by-step solved examples, and practice with real exam-grade mock test sets.
1. Fundamentals & Definitions
- Matter: Anything that has mass and occupies space. Exists in states like solid, liquid, and gas.
- Pure Substance: Consists of only one type of particle (e.g., elements, compounds).
- Mixture: Consists of two or more substances physically mixed but not chemically combined.
- Element: A pure substance consisting of only one type of atom (e.g., Oxygen, Iron).
- Compound: A pure substance formed when two or more elements are chemically bonded together (e.g., Water - H₂O).
- Molecule: The smallest particle of an element or compound that can have a stable independent existence.
- Atom: The smallest unit of an element that maintains the properties of that element.
- Ion: An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.
- Valency: The combining power of an element.
- Physical Change: A change in which no new substance is formed, and which is often reversible (e.g., melting of ice).
- Chemical Change: A change that results in the formation of new chemical substances (e.g., rusting of iron).
2. Core Concepts & Formulas
Common Compounds
| Common Name | Chemical Name | Formula | Common Uses |
|---|---|---|---|
| Water | Dihydrogen Monoxide | H₂O | Universal solvent, essential for life processes. |
| Common Salt | Sodium Chloride | NaCl | Food preservation, food seasoning, chemical industry. |
| Baking Soda | Sodium Bicarbonate | NaHCO₃ | Antacid, baking, fire extinguisher. |
| Washing Soda | Sodium Carbonate | Na₂CO₃·10H₂O | Cleaning agent, softening hard water. |
| Bleaching Powder | Calcium Oxychloride | CaOCl₂ | Bleaching textiles, disinfectant, water treatment. |
| Quick Lime | Calcium Oxide | CaO | Manufacturing of cement and glass. |
| Slaked Lime | Calcium Hydroxide | Ca(OH)₂ | Whitewashing, neutralizing acidic soil. |
| Plaster of Paris (POP) | Calcium Sulphate Hemihydrate | CaSO₄·½H₂O | Casts for fractures, molds, decorative materials. |
| Gypsum | Calcium Sulphate Dihydrate | CaSO₄·2H₂O | Manufacturing of cement and Plaster of Paris. |
| Vinegar | Acetic Acid (dilute) | CH₃COOH | Food preservative, flavoring agent. |
| Marble / Chalk | Calcium Carbonate | CaCO₃ | Building material, manufacturing of cement. |
Acids, Bases, and Salts
- Acid Properties: Sour taste, turn blue litmus paper red, have a pH below 7.
- Base Properties: Bitter taste, feel soapy to the touch, turn red litmus paper blue, have a pH above 7.
- Neutral Solution: Has a pH of exactly 7 (e.g., pure water).
- Indicators: Substances that change color to show whether a substance is an acid or a base (e.g., litmus, turmeric).
- Neutralization Reaction:
Acid + Base → Salt + Water - Important Acids: HCl (Hydrochloric acid), H₂SO₄ (Sulfuric acid), HNO₃ (Nitric acid), CH₃COOH (Acetic acid).
- Important Bases: NaOH (Sodium hydroxide), KOH (Potassium hydroxide), Ca(OH)₂ (Calcium hydroxide), NH₄OH (Ammonium hydroxide).
Chemical Reactions
- Combination: Two or more reactants combine to form a single product. (e.g.,
CaO + H₂O → Ca(OH)₂) - Decomposition: A single compound breaks down into two or more simpler substances.
- Displacement: A more reactive element displaces a less reactive element from its compound.
- Double Displacement: An exchange of ions between two compounds.
- Oxidation: Addition of oxygen or removal of hydrogen.
- Reduction: Removal of oxygen or addition of hydrogen.
- Exothermic: A reaction that releases heat.
- Endothermic: A reaction that absorbs heat.
Metals and Non-metals
- Properties of Metals: Lustrous (shiny), malleable (can be beaten into sheets), ductile (can be drawn into wires), good conductors of heat and electricity.
- Properties of Non-metals: Generally non-lustrous, brittle, poor conductors.
- Exceptions: Graphite (a non-metal) is a good conductor of electricity. Iodine (a non-metal) is lustrous.
- Reactivity Series: A list of metals arranged in order of decreasing reactivity: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au.
- Corrosion: The deterioration of a metal as a result of chemical reactions with its environment. Rusting of iron is a common example.
Carbon and Its Compounds
- Carbon Basics: Exhibits tetravalency (can form 4 bonds) and catenation (can form long chains with other carbon atoms).
- Hydrocarbons: Compounds of carbon and hydrogen.
- Saturated: Contain only single bonds (e.g., Methane, Ethane).
- Unsaturated: Contain double or triple bonds (e.g., Ethene, Ethyne).
- Polymers: Large molecules made of repeating smaller units called monomers (e.g., plastic, rubber, PVC).
- Fuels: Coal, petroleum, LPG (Liquefied Petroleum Gas), CNG (Compressed Natural Gas).
Must-Know Fact Sheet
| Area | Key Points |
|---|---|
| pH Scale | pH < 7 is acidic, pH = 7 is neutral, pH > 7 is basic. |
| Neutralization | Acid + Base → Salt + Water. |
| Rusting | Iron + Oxygen + Moisture → Hydrated Iron (III) Oxide. |
| Photosynthesis | CO₂ + H₂O → (in presence of sunlight) Glucose + Oxygen. |
| Hard vs Soft Water | Hard water contains dissolved mineral ions (like calcium and magnesium) and does not lather easily with soap. |
| Water Purification | Methods include chlorination, boiling, and filtration. |
| Fertilizers | Key components are often Nitrogen (N), Phosphorus (P), and Potassium (K) - NPK. |
Solved Examples
1Example 1 (Easy)
Question: Which compound is commonly known as Baking Soda and is used as an antacid?
2Example 2 (Moderate)
Question: The process of rusting of an iron pipe is an example of which type of chemical reaction?
3Example 3 (Hard)
Question: What happens when a piece of zinc metal is dropped into a blue-colored solution of copper sulfate? Explain with the reaction type.