1. Acids and Bases: Introduction
- Acids: Substances that release H⁺ ions in aqueous solution.
🔸 Taste: Sour
🔸 Example: HCl, H₂SO₄, CH₃COOH - Bases: Substances that release OH⁻ ions in aqueous solution.
🔹 Taste: Bitter, slippery to touch
🔹 Example: NaOH, KOH, NH₄OH
2. Indicators
- Definition: Substances that change color in acidic/basic solutions.
Indicator | Acid Color | Base Color |
Litmus | Red | Blue |
Methyl Orange | Red | Yellow |
Phenolphthalein | Colorless | Pink |
Turmeric | Yellow | Reddish-Brown |
3. Chemical Properties of Acids and Bases
a) Reaction with Metals
- Acid + Metal → Salt + H₂ (Hydrogen gas)
- Test for H₂ gas: Burning matchstick gives a ‘pop’ sound.
Example:
Zn + 2HCl → ZnCl₂ + H₂↑
b) Reaction with Metal Carbonates and Bicarbonates
- Produces CO₂ gas, Salt, and Water.
- CO₂ turns lime water milky.
Example:
Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O
c) Reaction with Metal Oxides
- Acid + Metal Oxide → Salt + Water
(Metal oxides are basic in nature.)
Example:
CuO + H₂SO₄ → CuSO₄ + H₂O
d) Reaction of Base with Non-metal Oxides
- Base + Non-metal oxide → Salt + Water
(Non-metal oxides are acidic.)
Example:
Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
4. Acid-Base Reaction (Neutralization)
- Acid + Base → Salt + Water
Exothermic reaction.
Example:
HCl + NaOH → NaCl + H₂O
5. pH Scale
- pH: Potential of Hydrogen, ranges from 0 to 14.
- pH < 7: Acidic
- pH = 7: Neutral
- pH > 7: Basic
Importance of pH in Everyday Life:
- Soil treatment (acidic soil treated with lime)
- Tooth decay (caused by acid below pH 5.5)
- Digestion (stomach acid — HCl)
- Self-defense in animals (e.g., wasp stings are basic; bee stings are acidic)
🧂 6. Salts
- Definition: Ionic compounds formed by neutralization of an acid with a base.
Examples of Important Salts:
|
Salt |
Formula |
Use |
|
Sodium chloride |
NaCl |
Table salt |
|
Sodium carbonate |
Na₂CO₃ |
Washing soda |
|
Sodium bicarbonate |
NaHCO₃ |
Baking soda |
|
Calcium carbonate |
CaCO₃ |
Marble, chalk |
|
Calcium hydroxide |
Ca(OH)₂ |
Slaked lime |
|
Plaster of Paris |
CaSO₄·½H₂O |
Fracture casts |
🏗️ 7. Important Compounds
🔸 a) Washing Soda (Na₂CO₃·10H₂O)
- Prepared by heating baking soda.
- Removes hardness of water.
🔹 b) Baking Soda (NaHCO₃)
- Mild base.
- Used in baking, fire extinguishers.
🔸 c) Plaster of Paris (POP) (CaSO₄·½H₂O)
- Formed by heating gypsum:
CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O
- Used for making molds, casts.
💎 8. Important Reactions to Remember
- NaOH + HCl → NaCl + H₂O (Neutralization)
- Ca(OH)₂ + CO₂ → CaCO₃ + H₂O (CO₂ test)
- Zn + H₂SO₄ → ZnSO₄ + H₂ (Hydrogen gas)
- CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O (POP formation)
✅ 9. Mind Map / Summary
Acids → Sour → H⁺ ions → React with metals, bases, oxides.
Bases → Bitter → OH⁻ ions → React with acids, non-metal oxides.
Salts → Formed from Acid + Base → Examples: NaCl, Na₂CO₃, CaSO₄.
Frequently Asked Questions (FAQs) from “Acids, Bases and Salts” — CBSE Class 10 Board Exam
🔹 Very Short Answer Type Questions (1-2 Marks)
- Define acids and bases with examples.
- What is the pH of acidic, neutral, and basic solutions?
- Why does dry HCl gas not change the color of litmus paper?
- What is the chemical name and formula of baking soda?
- Name the acid present in:
- Vinegar
- Tamarind
- Why do we feel a burning sensation when an ant stings?
- Write the chemical formula of Plaster of Paris.
- Name the acid produced in the stomach that aids digestion.
🔸 Short Answer Type Questions (3 Marks)
- Write the chemical equation for the reaction of:
- HCl with zinc
- Na₂CO₃ with HCl
- List three chemical properties of acids.
- What happens when CO₂ is passed through lime water? Explain with an equation.
- Explain the importance of pH in everyday life with examples.
- Write the steps involved in the preparation of baking soda.
🔶 Long Answer Type Questions (5 Marks)
- Describe the chemical properties of acids with suitable chemical equations.
- Explain the chemical properties of bases with examples.
- Describe the preparation, properties, and uses of:
- Plaster of Paris (POP)
- Washing soda
- Explain the working of the pH scale and its significance.
- Explain neutralization with examples and a labeled diagram if possible.
📝 Common Diagram-Based Questions
- Draw a pH scale and label acidic, neutral, and basic ranges.
- Show the reaction of CO₂ with lime water in a diagrammatic form.
⭐ Most Repeated Questions
- What is the chemical name and formula of POP?
- Write the balanced equation for the reaction of zinc with HCl.
- Explain the importance of pH in tooth decay and soil treatment.
🎯 Tip:
Focus on reactions involving:
- Metals with acids
- Acids with carbonates/bicarbonates
- Neutralization reactions
- Importance of pH in daily life