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Welcome to Class 10 Chemistry

Class 9 showed you what matter is made of. Class 10 Chemistry is about how matter changes — reactions, acids and bases, metals, and the carbon compounds of life and industry.

1. From what matter is to how matter changes

In Class 9 you learned that everything around you is made of atoms, that atoms join to form molecules and ions, and that every pure substance has a formula — $\mathrm{H_{2}O}$, $\mathrm{NaCl}$, $\mathrm{CO_{2}}$. That is the alphabet of chemistry. Class 10 teaches you to read and write its sentences: what happens when substances meet, which new substances form, and how much of each is involved.

The course follows the four chemistry chapters of the CBSE Class 10 Science syllabus. You will write and balance chemical equations, sort reactions into families and meet oxidation and reduction (Chapter 1); test acids and bases with indicators and the pH scale and make useful salts (Chapter 2); compare metals and non-metals, see why some metals are extracted with carbon and others only by electricity, and fight corrosion (Chapter 3); and explore carbon, the element of fuels, plastics, soaps and life itself (Chapter 4).

📦 Class 9 gave you…

symbols, valency and formulas: $$\mathrm{Na^{+}\ Cl^{-} \rightarrow NaCl},\qquad \mathrm{Al^{3+}\ O^{2-} \rightarrow Al_{2}O_{3}}$$

🚀 Class 10 begins with…

equations that obey conservation of mass: $$\mathrm{4Al(s) + 3O_{2}(g) \rightarrow 2Al_{2}O_{3}(s)}$$

2. A day full of chemistry

Follow one ordinary school day and you will meet every chapter of this course before lunch.

☕ 6:30 am · Chapter 1The gas stove burns LPG: $\mathrm{2C_{4}H_{10} + 13O_{2} \rightarrow 8CO_{2} + 10H_{2}O}$. A tin of cooking oil left open for weeks turns rancid — an oxidation.
🪥 7:00 am · Chapter 2Toothpaste is basic and neutralises the acids that bacteria make in your mouth; tooth enamel starts to dissolve below pH 5.5.
🚲 7:30 am · Chapter 3The iron chain of your bicycle rusts in the rain, but its galvanised, zinc-coated parts do not.
🧼 1:00 pm · Chapter 4Soap lifts the curry stain off your shirt: its molecules have a water-loving head and an oil-loving carbon tail.

Every one of these is a chemical change that can be written as an equation, and every equation is built from correct formulas. That is why the course starts with a quick refresher on formulas. The chapter introductions — 1, 2, 3, 4 — give the map of each chapter.

3. Warm-up: building formulas from ions

An ionic compound is electrically neutral: the total positive charge of its cations must cancel the total negative charge of its anions. The size of an ion's charge is its valency. To write the formula, take just enough of each ion for the charges to cancel — the familiar “criss-cross” of valencies is a shortcut for exactly that.

Interactive 1 — Formula Builder: Make the Charges Cancel

Choose a cation and an anion. The lab brings in just enough of each ion for the positive and negative charges to balance — the two bars must end equal — and writes the formula and the name.

formula—
name—
total positive charge—
total negative charge—
✏️ Example 1 — Writing a formula by balancing charges
Write the formulas of (a) aluminium sulphate and (b) calcium phosphate.
Ions (a) $\mathrm{Al^{3+}}$ and $\mathrm{SO_{4}^{2-}}$. The smallest charge both can make is $6$: two $\mathrm{Al^{3+}}$ give $+6$, three $\mathrm{SO_{4}^{2-}}$ give $-6$.
Formula $\mathrm{Al_{2}(SO_{4})_{3}}$ — the bracket shows that the subscript 3 multiplies the whole sulphate group.
(b) $\mathrm{Ca^{2+}}$ and $\mathrm{PO_{4}^{3-}}$: three $\mathrm{Ca^{2+}}$ give $+6$ and two $\mathrm{PO_{4}^{3-}}$ give $-6$, so $\mathrm{Ca_{3}(PO_{4})_{2}}$ — the main mineral in your bones and teeth.
Check (a) $2(+3)+3(-2)=0$ ✓; (b) $3(+2)+2(-3)=0$ ✓.
✏️ Example 2 — Counting atoms and formula mass
How many atoms of each element are there in one formula unit of calcium hydroxide, $\mathrm{Ca(OH)_{2}}$ (slaked lime, used in whitewash)? Find its formula mass, using $\mathrm{Ca}=40\ \mathrm{u}$, $\mathrm{O}=16\ \mathrm{u}$, $\mathrm{H}=1\ \mathrm{u}$.
Count The 2 outside the bracket doubles everything inside: 1 Ca, 2 O and 2 H — 5 atoms in all.
Mass $40+2\times16+2\times1=74\ \mathrm{u}$.
Why it matters Counting atoms correctly inside brackets is exactly the skill you need to balance equations in Section 1.1.
🧭 How to use this course
  • Read with a pen and a notebook. Try every worked example yourself before opening its solution, then compare step by step.
  • Play with the labs. Each section has two interactives — balance equations atom by atom, slide along the pH scale, race metals against each other. Predict what will happen before you press ▶ Play.
  • Do the exercises in order. They run from routine to challenging, and every part has a full solution.
  • Practise for the board exam. Every section has a 🎯 Exam corner of board-style questions (MCQ, assertion–reason, case-based, short and long answers), with an occasional JEE / NEET foundation problem.
  • Two kinds of extra boxes. A 🚀 box goes beyond the board syllabus and names the entrance exams that list its topic; board-only students may skip it. A 📘 box (periodic classification of elements, in Section 3.2) is in the CBSE syllabus and tested in school, but not in the year-end board exam.
  • Use the quiz as a gate. Five questions end every section; if you score below 4, reread before moving on.
  • Look up words. Dotted words show their meaning when you tap them. The Glossary and Formula Sheet collect every term and key equation in one place.

4. Readiness check — are you ready?

Eight quick questions on the Class 9 ideas this course uses most. Answer all of them; for each one you miss you will get a short reminder.

Q1. The formula of calcium chloride is
Q2. The valency of aluminium in $\mathrm{Al_{2}O_{3}}$ is
Q3. The formula of ammonium sulphate is
Q4. How many atoms are there in one molecule of $\mathrm{H_{2}SO_{4}}$?
Q5. The molecular mass of $\mathrm{CO_{2}}$ ($\mathrm{C}=12\ \mathrm{u}$, $\mathrm{O}=16\ \mathrm{u}$) is
Q6. The symbol of sodium is
Q7. Which of these is a compound?
Q8. Solid sodium chloride is made of

When you are ready, start with Chapter 1 — Chemical Reactions and Equations. When you finish this course, Class 11 Chemistry takes every idea here further.

← Class 10 Chemistry — ContentsChapter 1 — Chemical Reactions and Equations →