Chemistry Basics – Puducherry PSC
(General Awareness & Current Affairs)
Purpose – To give a quick, clear overview of the fundamentals of chemistry that frequently appear in PSC exams and in general‑awareness questions.
1. Simple Explanation
Chemistry is the science that studies the composition, structure, properties, and changes of matter.
In the PSC syllabus we need to know:
| Area | What it covers | Why it matters for PSC |
|---|---|---|
| Atoms & Elements | Structure of atoms, periodic table trends | Basic facts about elements and their uses |
| Chemical Bonding | Ionic, covalent, metallic | Explains how substances are formed |
| States of Matter & Changes | Solids, liquids, gases, phase changes | Common processes (e.g., heating water) |
| Acids, Bases & Salts | pH, neutralisation | Everyday chemistry (food, medicine) |
| Solutions & Concentrations | Molarity, normality | Nutrients in water, industrial solutions |
| Redox Chemistry | Oxidation‑reduction, galvanic cells | Batteries, corrosion |
| Chemical Equilibrium | Le Chatelier’s principle | Catalysts, industrial processes |
| Thermodynamics | Enthalpy, entropy | Energy in combustion, refrigeration |
| Basic Analytical Techniques | Titration, spectroscopy | Quality control, environmental testing |
2. Key Points
| Topic | Important Facts & Terms |
|---|---|
| Atomic Structure | • Protons (+1), neutrons (0), electrons (‑1) • Atomic number = protons • Mass number = protons + neutrons • Isotopes: same element, different neutrons |
| Periodic Table | • Periodic trends: electronegativity ↑ left→right, ionization energy ↑, atomic radius ↓ • Groups: 1 – Alkali metals, 2 – Alkaline earth, 17 – Halogens, 18 – Noble gases |
| Types of Bonding | • Ionic: electron transfer (metal + non‑metal) • Covalent: electron sharing (non‑metals) • Metallic: delocalised electrons (metals) |
| States of Matter | • Solid: fixed shape & volume • Liquid: fixed volume, takes container shape • Gas: neither fixed shape nor volume |
| Phase Changes | • Melting (solid→liquid) • Freezing (liquid→solid) • Vaporisation (liquid→gas) • Condensation (gas→liquid) • Sublimation (solid→gas) |
| Acids & Bases | • Acid (H⁺ donor) – pH < 7 • Base (OH⁻ donor) – pH > 7 • Neutralisation: acid + base → salt + water |
| Solution Concentration | • Molarity (M) = moles solute / litres solution • Normality (N) = equivalents / litre (important for acid‑base reactions) |
| Redox Reactions | • Oxidation: loss of electrons • Reduction: gain of electrons • Galvanic cell: spontaneous redox, gives electric current |
| Equilibrium | • Dynamic balance: forward = reverse • Le Chatelier’s principle: system shifts against change in concentration, pressure, temperature |
| Thermodynamics | • ΔH (enthalpy) – heat content • ΔS (entropy) – disorder • ΔG = ΔH – TΔS (Gibbs free energy; ΔG < 0 = spontaneous) |
| Common Analytical Methods | • Titration (acid–base, redox) • Spectrophotometry (colour intensity ↔ concentration) • Chromatography (separating mixtures) |
3. Worked Example
Problem:
A 0.25 M solution of hydrochloric acid (HCl) is titrated with a 0.10 M sodium hydroxide (NaOH) solution. How many millilitres of NaOH are required to neutralise 50 ml of the HCl solution?
Solution:
-
Write the neutralisation reaction
[ \text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O} ]
Stoichiometry: 1 : 1.
-
Find moles of HCl in 50 ml
[ \text{Moles HCl} = 0.25,\text{M} \times 0.050,\text{L} = 0.0125,\text{mol} ]
-
Same moles of NaOH needed (1 : 1)
[ \text{Moles NaOH required} = 0.0125,\text{mol} ]
-
Convert to volume of 0.10 M NaOH
[ \text{Volume} = \frac{\text{Moles}}{\text{Concentration}} = \frac{0.0125}{0.10} = 0.125,\text{L} = 125,\text{ml} ]
Answer: 125 ml of 0.10 M NaOH are required to neutralise 50 ml of 0.25 M HCl.
4. Quick Revision Summary
| Concept | Recall Point |
|---|---|
| Atomic number | Number of protons – unique identity |
| Periodic trends | Electronegativity ↑ right, radius ↓ |
| Bond types | Ionic (metal + non‑metal), covalent (non‑metal + non‑metal), metallic (metal) |
| Phase changes | Melting, freezing, vaporisation, condensation, sublimation |
| pH scale | <7 acid, >7 base, =7 neutral |
| Molarity | Moles solute per litre solution |
| Redox | Oxidation = loss of |