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General Chemistry

The Hook: The Salt That Built an Empire

In 1930, a frail man in a loincloth walked 240 miles to the sea at Dandi and picked up a handful of salt. That single act shook the British Empire. But have you ever wondered — what *is* salt, chemically? Why did the British tax it so heavily? Because sodium chloride (NaCl) is not just a seasoning — it is a compound so essential that life, industry, and even revolutions have been built around it.

Chemistry is not a subject locked in laboratories. It is in the iron that rusts on your gate, the baking soda in your kitchen, the LPG cylinder in your home, and the oxygen in your lungs. And in every competitive exam — SSC, Railway, Banking, State PCS — General Chemistry questions appear again and again, testing exactly these everyday substances.

This chapter will make you see chemistry everywhere — and score everywhere too.

🎯 Learning Objectives

By the end of this chapter, you will be able to:

1. Classify matter into elements, compounds, and mixtures — and spot exam traps between them.
2. Recall the most-asked elements, their symbols, and their discoverers.
3. Explain acids, bases, and salts with everyday examples and pH values.
4. Identify common chemical compounds by their common names (a favourite exam area!).
5. Understand metals, non-metals, and important alloys.
6. Answer questions on gases, fuels, and basic organic chemistry confidently.

1. Matter and Its Classification

Everything around you that has mass and occupies space is matter. Matter exists in three common states — solid, liquid, and gas (plasma and Bose-Einstein condensate are advanced states, rarely asked at this level).

Matter is classified as:

• Element — a pure substance made of only one kind of atom. Cannot be broken down further by chemical means. Example: Oxygen (O), Gold (Au), Iron (Fe). There are 118 known elements, of which 94 occur naturally.
• Compound — two or more elements chemically combined in a fixed ratio. Example: Water (H₂O), Carbon dioxide (CO₂), Salt (NaCl).
• Mixture — two or more substances physically mixed, in any ratio. Can be separated by physical methods. Example: Air, milk, soil, brass.

Key distinction the examiner loves: A compound has properties *completely different* from its constituent elements. Sodium is a violently reactive metal; chlorine is a poisonous gas — yet their compound, common salt, sits peacefully on your dining table!

🧠 Active Recall: Is air an element, compound, or mixture? Is water? Why can a mixture be separated physically but a compound cannot?

2. Elements, Symbols, and the Periodic Table

Chemical Symbols — Where Do They Come From?

Many symbols come from Latin names, and this is a classic exam trap:

🪄 Mnemonic for Latin-symbol elements: "Navratri Ke Feast mein Cup Ag Au Hg Pb Snack Wala" — silly, but you will never forget that these ten symbols don't match their English names!

The Periodic Table

• Developed by Dmitri Mendeleev (1869), who arranged elements by atomic mass and predicted undiscovered elements.
• The modern periodic table (based on Moseley's work) arranges elements by atomic number (number of protons).
• 18 groups (vertical columns) and 7 periods (horizontal rows).
• Group 1 — Alkali metals (very reactive: Na, K)
• Group 17 — Halogens (F, Cl, Br, I)
• Group 18 — Noble gases (He, Ne, Ar, Kr, Xe, Rn) — chemically inert, hence called "noble."

🧠 Active Recall: Why is the symbol of potassium 'K' and not 'P'? Who gave the modern periodic law based on atomic number?

3. Acids, Bases, and Salts — The Heart of Exam Chemistry

Acids

• Sour in taste, turn blue litmus red.
• Release H⁺ ions in water.
• Examples: Hydrochloric acid (HCl) — present in our stomach; Sulphuric acid (H₂SO₄) — called the "King of Chemicals"; Nitric acid (HNO₃); Acetic acid (CH₃COOH) — in vinegar; Citric acid — in lemons; Lactic acid — in curd/sour milk.

Bases

• Bitter in taste, soapy to touch, turn red litmus blue.
• Examples: Sodium hydroxide (NaOH) — caustic soda; Potassium hydroxide (KOH) — caustic potash; Calcium hydroxide (Ca(OH)₂) — slaked lime; Ammonium hydroxide — in window cleaners.
• Bases soluble in water are called alkalis.

The pH Scale

• Ranges from 0 to 14.
• pH 7 = neutral (pure water).
• pH < 7 = acidic; pH > 7 = basic.
• Human blood pH ≈ 7.4 (slightly alkaline).
• pH was introduced by Sørensen.

Salts and Neutralisation

Acid + Base → Salt + Water (Neutralisation reaction)

Famous salts (memorise this table — it appears in every exam!):

🪄 Mnemonic for vitriols: "Blue Copper, Green Iron, White Zinc" — Blue vitriol = Copper, Green vitriol = Iron (ferrous), White vitriol = Zinc.

🧠 Active Recall: What is the chemical formula of washing soda? Which acid is present in the stomach? What is the pH of pure water?

4. Metals, Non-Metals, and Alloys

Metals

• Lustrous, malleable (can be beaten into sheets), ductile (drawn into wires), good conductors of heat and electricity.
• Most ductile metal: Gold. Best conductor of electricity: Silver (then copper).
• Mercury is the only metal liquid at room temperature (Gallium also melts near room temperature).
• Most abundant metal in Earth's crust: Aluminium. Most abundant element overall: Oxygen.

Non-Metals

• Generally brittle, non-lustrous, poor conductors.
• Exception (exam favourite!): Graphite (a form of carbon) is a good conductor of electricity — that's why it's used in electrodes.
• Diamond (also carbon!) is the hardest natural substance and a *non-conductor*.
• Bromine is the only non-metal liquid at room temperature.

Important Alloys

⚠️ Trap alert: German silver contains no silver at all — examiners love this!

🧠 Active Recall: Which non-metal conducts electricity? What is the composition of bronze? Why is duralumin used in aircraft?

5. Important Gases and Fuels

• Oxygen (O₂): Supports combustion; discovered by Joseph Priestley (named by Lavoisier).
• Hydrogen (H₂): Lightest element; discovered by Henry Cavendish; called "inflammable air."
• Nitrogen (N₂): ~78% of air; discovered by Daniel Rutherford; used in fertilizers (urea).
• Carbon dioxide (CO₂): Used in fire extinguishers; solid CO₂ = dry ice.
• Laughing gas (N₂O): Used as an anaesthetic; discovered by Priestley, anaesthetic use by Humphry Davy.
• LPG: Mainly propane and butane; the smell comes from added ethyl mercaptan (a safety measure — LPG itself is odourless!).
• CNG: Mainly methane (CH₄) — the cleanest fossil fuel.
• Biogas: Mainly methane, produced from cow dung/organic waste.
• Tear gas: Chloropicrin / CS gas.
• Mustard gas: A chemical warfare agent (sulphur-based).

🧠 Active Recall: Why does LPG smell if it is odourless? Which gas is called laughing gas? What is the main component of CNG?

6. Carbon and Its Allotropes

• Allotropes = different physical forms of the same element.
• Carbon's allotropes: Diamond (hardest, non-conductor), Graphite (soft, conductor, used in pencil leads and lubricants), Fullerene (Buckminsterfullerene, C₆₀).
• Pencil "lead" contains no lead — it is graphite mixed with clay. (Another classic trap!)

7. Basic Organic Chemistry

• Organic chemistry = chemistry of carbon compounds (term linked to "vital force theory," broken by Wöhler in 1828 when he synthesised urea from an inorganic compound).
• Methane (CH₄): Simplest hydrocarbon; marsh gas.
• Ethanol (C₂H₅OH): Alcohol in beverages; used in hand sanitisers.
• Methanol (CH₃OH): Poisonous — causes blindness/death (spurious liquor tragedies).
• Formaldehyde (HCHO): Used to preserve biological specimens (formalin).
• Chloroform (CHCl₃): Early anaesthetic.
• Iodoform (CHI₃): Antiseptic.

🔗 Static-Dynamic Link

Green Hydrogen Mission: Hydrogen — the lightest element you studied above — is at the centre of India's National Green Hydrogen Mission (approved 2023), which aims to make India a hub for hydrogen produced using renewable energy. When exams ask "which element is called the fuel of the future," the answer is hydrogen — a static fact with a live current-affairs connection.

🗣️ Linguistic Bridge: In Hindi We Say This, In English We Say That

⚠️ Caution: Examiner's Trap

Trap 1 — "लगभग सही कथन" (Almost-Correct Statement):
"German silver is an alloy of copper, zinc, and silver." — Sounds 90% right, but German silver contains nickel, not silver. Similarly: "Pencil lead contains lead" — wrong, it's graphite. The examiner changes just one word in a true statement.

Trap 2 — "समान नाम/वर्ष" (Similar Names Confusion):
Washing soda (Na₂CO₃) vs Baking soda (NaHCO₃) vs Caustic soda (NaOH) — three "sodas," three different compounds. Similarly, Quicklime (CaO) vs Slaked lime (Ca(OH)₂) vs Limestone (CaCO₃). Examiners deliberately place these side by side in options.

Trap 3 — "नकारात्मक वाक्यांश" (Hidden Negative):
"Which of the following is NOT an allotrope of carbon?" or "All are alloys EXCEPT." Students who read fast mark the first correct-looking option (diamond, brass) and lose the mark. Always circle the NOT/EXCEPT before reading options.

📋 High-Yield Facts Table (Revise Daily!)

📅 Revision Planner

🔁 Review after 2 days: Blurt out (write from memory) the table of common names & formulas (salt, soda, lime, vitriols) and the 10 Latin-symbol elements. Check against the chapter. Whatever you missed — that's your weak zone.

🔁 Weekly review: Attempt one practice set. Re-read only the sections where you made mistakes. Re-blurt the alloys table and gases list.

🔁 Monthly blurting: Take a blank sheet. Write everything you remember about: (1) acids-bases-salts, (2) alloys, (3) gases & fuels, (4) periodic table facts. Compare with the chapter. Three rounds of this, and General Chemistry becomes your highest-scoring section.

Remember: Chemistry in exams is not about understanding reactions deeply — it's about remembering names, formulas, and exceptions. And exceptions are exactly where the examiner hides. Master the exceptions, and you master the exam. 💪