Acids, Bases and Salts Class 10: Complete Notes, Reactions, pH & Important Questions
Acids, Bases and Salts is one of the most important chapters in Class 10 Chemistry. It connects everyday substances such as lemon juice, soap, baking soda and antacids with concepts such as indicators, pH, neutralisation, salts and chemical reactions.
These Class 10 notes cover the chapter in a revision-friendly format with definitions, important reactions, balanced equations, pH concepts, common salts, uses, solved examples, exam mistakes and frequently asked questions.
- What Are Acids, Bases and Salts?
- Indicators and Their Colour Changes
- Important Reactions of Acids
- Important Reactions of Bases
- pH Scale and Its Importance
- Important Salts for Class 10
- Baking Soda
- Washing Soda
- Bleaching Powder
- Plaster of Paris
- Water of Crystallisation
- Acids, Bases and Salts in Everyday Life
- Common Exam Mistakes
- One-Minute Revision Table
- Important Class 10 Questions
- Frequently Asked Questions
1. What Are Acids, Bases and Salts?
An acid is a substance that produces hydrogen ions in aqueous solution. For Class 10 Chemistry, acids can be recognised through their characteristic reactions and indicator changes. Common examples include hydrochloric acid (HCl), sulphuric acid (H2SO4) and nitric acid (HNO3).
A base is a substance that produces hydroxide ions in aqueous solution. Common bases include sodium hydroxide (NaOH), calcium hydroxide [Ca(OH)2] and magnesium hydroxide [Mg(OH)2].
A salt is an ionic compound that can be formed when an acid reacts with a base. Common salts studied in this chapter include sodium chloride, baking soda, washing soda, bleaching powder and plaster of Paris.
| Substance | Example | Typical Indicator Behaviour |
|---|---|---|
| Acid | HCl | Blue litmus → red |
| Base | NaOH | Red litmus → blue |
| Neutral substance | Pure water | Litmus generally shows no change |
| Salt | NaCl | Depends on the salt and solution |
2. Indicators and Their Colour Changes
An indicator is a substance that changes colour depending on whether a solution is acidic or basic. Indicators are useful because they allow us to identify the nature of a solution without tasting it.
| Indicator | Acidic Medium | Basic Medium |
|---|---|---|
| Blue litmus | Turns red | Remains blue |
| Red litmus | Remains red | Turns blue |
| Phenolphthalein | Colourless | Pink |
| Methyl orange | Red | Yellow |
| Universal indicator | Shows different colours across the pH scale | |
3. Important Reactions of Acids
3.1 Acid + Metal → Salt + Hydrogen
Many acids react with suitable metals to release hydrogen gas and form a salt.
Here zinc reacts with hydrochloric acid to produce zinc chloride and hydrogen gas.
3.2 Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
3.3 Acid + Metal Hydrogen Carbonate → Salt + Water + Carbon Dioxide
Carbon dioxide can be identified because it turns limewater milky.
3.4 Acid + Base → Salt + Water
This is called a neutralisation reaction.
4. Important Reactions of Bases
4.1 Base + Acid → Salt + Water
4.2 Base + Non-Metal Oxide → Salt + Water
This reaction is particularly useful for understanding why carbon dioxide is described as an acidic oxide.
5. pH Scale: The Most Important Concept
The pH scale is used to express the acidity or basicity of an aqueous solution. At the Class 10 level, the scale is commonly represented from 0 to 14.
| pH | Nature of Solution |
|---|---|
| Less than 7 | Acidic |
| 7 | Neutral |
| Greater than 7 | Basic / Alkaline |
A lower pH generally indicates a higher concentration of hydrogen ions in an aqueous solution. The NCERT Class 10 chapter explains pH as a measure related to hydrogen-ion concentration. :contentReference[oaicite:10]{index=10}
6. Strong and Weak Acids
A strong acid ionises extensively in aqueous solution, while a weak acid ionises only partially. Strength should not be confused with concentration.
| Concept | Meaning |
|---|---|
| Strong acid | Ionises extensively in water |
| Weak acid | Ionises partially in water |
| Concentrated solution | Contains a relatively large amount of solute |
| Dilute solution | Contains a relatively smaller amount of solute |
7. Important Salts in Class 10 Chemistry
Several salts have important laboratory, industrial and household applications. The following compounds are especially useful for Class 10 examination revision.
| Salt | Formula | Common Name / Use |
|---|---|---|
| Sodium chloride | NaCl | Common salt |
| Sodium hydrogen carbonate | NaHCO3 | Baking soda |
| Sodium carbonate decahydrate | Na2CO3·10H2O | Washing soda |
| Calcium oxychloride | CaOCl2 | Bleaching powder |
| Calcium sulphate hemihydrate | CaSO4·½H2O | Plaster of Paris |
8. Baking Soda — NaHCO₃
Baking soda is sodium hydrogen carbonate, represented by NaHCO3. It is commonly used in baking and is also used in some antacid formulations.
Heating of Baking Soda
The carbon dioxide released in this reaction helps dough or batter expand during baking.
9. Washing Soda — Na₂CO₃·10H₂O
Washing soda is sodium carbonate containing water of crystallisation. It is represented as:
It has applications as a cleaning agent and in several industrial processes.
10. Bleaching Powder
Bleaching powder is commonly represented at school level by the formula CaOCl2. It is associated with bleaching and disinfecting applications.
For examination purposes, remember its formula, common name and major uses.
11. Plaster of Paris
Plaster of Paris is calcium sulphate hemihydrate:
When mixed with water, it sets into gypsum:
Plaster of Paris is used for making casts, moulds and decorative materials.
12. What Is Water of Crystallisation?
Water of crystallisation is the fixed number of water molecules associated with one formula unit of a crystalline salt.
For example, washing soda contains ten water molecules:
Copper sulphate crystals are another familiar example:
13. Acids, Bases and Salts in Everyday Life
Indigestion and Antacids
Excess acid in the stomach can cause discomfort. Antacids contain basic substances that react with excess acid and help neutralise it.
Tooth Decay
Tooth enamel can be damaged when the mouth becomes sufficiently acidic. Maintaining oral hygiene and limiting frequent exposure to sugary foods can help reduce the conditions associated with tooth decay.
Soil pH
The pH of soil affects plant growth. Farmers and gardeners may need to consider whether soil is too acidic or too basic for particular crops.
Bee Stings and Acidic Substances
Certain insect stings can involve acidic substances, which is why neutralisation is often discussed in school-level applications of acids and bases. In real first-aid situations, however, the appropriate treatment depends on the insect and local medical guidance.
14. Dilution of Acids and Bases
Diluting a concentrated acid or base with water can release considerable heat. Therefore, laboratory safety matters.
15. Acids, Bases and Salts — Important Reaction Sheet
| Reaction | Equation |
|---|---|
| Acid + metal | Zn + 2HCl → ZnCl2 + H2 |
| Acid + carbonate | Na2CO3 + 2HCl → 2NaCl + H2O + CO2 |
| Acid + hydrogen carbonate | NaHCO3 + HCl → NaCl + H2O + CO2 |
| Acid + base | HCl + NaOH → NaCl + H2O |
| Base + non-metal oxide | Ca(OH)2 + CO2 → CaCO3 + H2O |
| Heating baking soda | 2NaHCO3 → Na2CO3 + H2O + CO2 |
16. Common Mistakes Students Make
- Confusing strong acids with concentrated acids.
- Writing the wrong formula for baking soda or washing soda.
- Forgetting that pH 7 is neutral.
- Mixing up red and blue litmus changes.
- Forgetting CO2 formation in acid-carbonate reactions.
- Writing an unbalanced chemical equation.
- Confusing baking soda with washing soda.
- Forgetting the water of crystallisation in hydrated salts.
- Writing Plaster of Paris as CaSO4·2H2O instead of CaSO4·½H2O.
- Learning reactions without understanding what type of reaction is occurring.
17. One-Minute Revision Table
| Topic | Remember |
|---|---|
| Acid | Produces H+ ions in aqueous solution |
| Base | Produces OH− ions in aqueous solution |
| Neutralisation | Acid + Base → Salt + Water |
| Acid + Metal | Salt + Hydrogen |
| Acid + Carbonate | Salt + Water + CO2 |
| pH < 7 | Acidic |
| pH = 7 | Neutral |
| pH > 7 | Basic |
| Baking soda | NaHCO3 |
| Washing soda | Na2CO3·10H2O |
| Bleaching powder | CaOCl2 |
| Plaster of Paris | CaSO4·½H2O |
18. Important Class 10 Questions
Question 1: What is neutralisation?
Neutralisation is the reaction between an acid and a base to form salt and water.
Question 2: What happens when an acid reacts with a metal carbonate?
It generally produces salt, water and carbon dioxide.
Question 3: What is the pH of a neutral solution?
At the standard school-level description of the pH scale, a neutral solution has pH 7.
Question 4: What is baking soda?
Baking soda is sodium hydrogen carbonate, NaHCO3.
Question 5: What is washing soda?
Washing soda is sodium carbonate decahydrate, Na2CO3·10H2O.
Question 6: What is Plaster of Paris?
Plaster of Paris is calcium sulphate hemihydrate, CaSO4·½H2O.
🎯 Try the Class 10 Mathematics 7-Day Demo Test Series — ₹10 Practice chapter-wise questions, detailed solutions and performance analysis.19. Related Class 10 Study Resources
20. Official References for Class 10 Chemistry
For textbook-level study, students should always cross-check the prescribed textbook and current board curriculum. The official NCERT Class 10 Science Chapter 2 covers acids, bases, salts, pH, neutralisation and water of crystallisation.
- NCERT Class 10 Science — Chapter 2: Acids, Bases and Salts
- CBSE Academic — Curriculum 2026–27
- NCERT Exemplar Problems
21. Frequently Asked Questions
What are acids and bases in Class 10?
Acids are substances that produce H+ ions in aqueous solution, while bases produce OH− ions in aqueous solution.
What is the pH scale?
The pH scale is used to express the acidity or basicity of an aqueous solution. At Class 10 level, pH below 7 is acidic, 7 is neutral and above 7 is basic.
What happens when an acid reacts with a metal?
A suitable acid can react with a metal to produce a salt and hydrogen gas. For example: Zn + 2HCl → ZnCl2 + H2.
What happens when an acid reacts with a metal carbonate?
An acid reacts with a metal carbonate to produce salt, water and carbon dioxide.
What is neutralisation?
Neutralisation is the reaction of an acid with a base to form salt and water.
What is baking soda?
Baking soda is sodium hydrogen carbonate, NaHCO3.
What is washing soda?
Washing soda is sodium carbonate decahydrate, Na2CO3·10H2O.
What is Plaster of Paris?
Plaster of Paris is calcium sulphate hemihydrate, CaSO4·½H2O.
What is water of crystallisation?
Water of crystallisation is the fixed number of water molecules associated with one formula unit of a crystalline salt.
Why should concentrated acid be added to water during dilution?
Dilution can release considerable heat. Adding acid slowly to water with stirring helps control the heat released and is the safer laboratory practice.
22. Final Revision Strategy
For fast revision, learn this chapter in four layers:
- Understand: acids, bases, indicators and pH.
- Practise: important reactions and balanced equations.
- Memorise: baking soda, washing soda, bleaching powder and Plaster of Paris.
- Apply: solve NCERT exercises and exam-style questions.
These notes are designed as a revision resource. For examination-specific requirements, students should follow their current school instructions and the latest official CBSE/NCERT curriculum and textbook.
