Here I am going to provide you CBSE Class 10 Science Chapter 2 Notes – Acids, Bases and Salts. You can also Download PDF of these notes. This chapter explains the nature, properties, and reactions of acids and bases. It discusses indicators, neutralization, pH scale, and preparation of salts. Students learn real-life applications like baking soda, bleaching powder, and plaster of Paris. It builds foundational understanding for chemistry and helps in daily life relevance. By going through Acids, Bases and Salts Class 10 Notes you will acquire a better command on this chapter. So, use these notes and do your best!!
Introduction
Acids and bases are not just chemical terms — they are active participants in reactions that shape everyday life. From fizzing tablets to baking cakes, the chemical behavior of acids and bases plays a crucial role. Let's dive into their chemical reactions in an easy, exam-friendly, and visual way.
1. Reaction of Acids with Metals
Reaction:
When acids react with metals, they liberate hydrogen gas and form salt.
General Reaction:
Acid + Metal → Salt + Hydrogen gas
Example:
Zn (s) + H₂SO₄ (aq) → ZnSO₄ (aq) + H₂ (g)
Observation: Bubbles of gas form in the test tube. If a burning matchstick is brought near, it makes a ‘pop’ sound — confirming the presence of H₂ gas.
Concept: Only metals that are more reactive than hydrogen can displace it from an acid.
2. Reaction of Bases with Metals
This reaction is less common, but some bases, especially strong ones like NaOH, can also react with certain metals to produce hydrogen gas and salt.
Example:
2Na + 2NaOH + 2H₂O → 2NaAlO₂ + 3H₂↑ (with aluminium)
Note: This is a specific reaction and doesn't occur with all metals or bases.
3. Reaction of Acids with Metal Carbonates and Metal Hydrogen Carbonates
Acids react with metal carbonates and metal hydrogen carbonates (bicarbonates) to produce:
- Salt
- Carbon dioxide gas (CO₂)
- Water
General Reaction:
Acid + Metal Carbonate → Salt + CO₂ + H₂O
Acid + Metal Hydrogen Carbonate → Salt + CO₂ + H₂O
Example:
Na₂CO₃ + 2HCl → 2NaCl + CO₂ + H₂O
NaHCO₃ + HCl → NaCl + CO₂ + H₂O
Observation: CO₂ gas turns lime water milky — this confirms carbon dioxide.
4. Reaction of Acids with Metal Oxides
Metal oxides are basic in nature. So, they neutralize acids and produce salt and water.
General Reaction:
Acid + Metal Oxide → Salt + Water
Example:
CuO (black) + HCl → CuCl₂ + H₂O
Concept: Metal oxides act as bases, proving that basicity is not only found in liquid substances like NaOH but also in solids like metal oxides.
5. Reaction of Bases with Non-metal Oxides
Non-metal oxides (like CO₂, SO₂) are acidic in nature. So they react with bases to form salt and water.
General Reaction:
Base + Non-metal Oxide → Salt + Water
Example:
Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
Insight: This reaction again shows that non-metal oxides are acidic, supporting the acid-base reaction theory.
LEARNING TABLE
| Type of Reaction | Reactants | Products | Real-life Example |
|---|---|---|---|
| Acid + Metal | HCl + Zn | ZnCl₂ + H₂ | Pickle reacting with metal lid |
| Acid + Metal Carbonate | HCl + NaHCO₃ | NaCl + CO₂ + H₂O | Antacids |
| Acid + Metal Oxide | HCl + CuO | CuCl₂ + H₂O | Metal cleaning |
| Base + Non-metal Oxide | Ca(OH)₂ + CO₂ | CaCO₃ + H₂O | CO₂ neutralized in lime water |
Takeaways:
- Hydrogen gas is always produced when acids react with active metals.
- Carbon dioxide is formed when acids meet carbonates/bicarbonates.
- Metal oxides behave like bases, while non-metal oxides act as acids.
- These reactions prove the neutralizing behavior of acids and bases in various forms.
How do Acids and Bases React with Water?
Understanding the Concept: Water Is Essential for Acids and Bases to Show Their True Nature
Did you know?
Acids and bases do not show their acidic or basic behavior unless they are dissolved in water.
This is because the presence of water allows acids and bases to ionize — they break into charged particles called ions, which are responsible for their characteristic properties.
1. Acids in Water – Ionization of Acids
When an acid is added to water, it releases hydrogen ions (H⁺).
These ions are responsible for the sour taste, corrosive nature, and their ability to turn blue litmus red.
Example:
HCl (Hydrochloric Acid) + H₂O → H⁺ (aq) + Cl⁻ (aq)
Here, HCl dissociates into H⁺ and Cl⁻ ions only in the presence of water.
Key Point:
Without water, HCl gas does not show acidic behavior. It must be in aqueous form (HCl(aq)).
2. Bases in Water – Ionization of Bases
When a base is dissolved in water, it releases hydroxide ions (OH⁻).
These OH⁻ ions are what make the solution bitter, slippery, and able to turn red litmus blue.
Example:
NaOH (Sodium Hydroxide) + H₂O → Na⁺ (aq) + OH⁻ (aq)
Just like acids, bases must be in aqueous form to exhibit their basic properties.
Case Study: Blue Litmus and Dry HCl Gas
The NCERT textbook gives a simple but powerful experiment to understand this concept:
Experiment:
Take a dry strip of blue litmus paper and bring it near dry HCl gas — no color change.
Now, moisten the litmus strip with water and expose it to HCl gas — it turns red.
Inference:
Dry HCl gas doesn't ionize (no H⁺ ions), so no acidic property. But with water, H⁺ ions are released, and the acid shows its nature.
Moral of the experiment:
Acids and bases need water to liberate ions, and ions cause the characteristic properties.
Why Water Matters? | The Ion Connection
| Substance | Without Water | With Water |
|---|---|---|
| HCl | No ionization, no acidity | Releases H⁺ → Shows acidic nature |
| NaOH | No ionization, no basicity | Releases OH⁻ → Shows basic nature |
This explains why dry substances may not act acidic or basic, even if they are chemically acids or bases.
Analogy:
Think of water like a power socket,
- The acid or base is the plug.
- Without plugging it in (adding water), the device (acid/base) won't work!
- Once plugged in (water is added), electricity (ions) flows and powers the action.
pH Scale – Measuring Acidity and Basicity
What is the pH Scale?
The pH scale is a special tool used to measure how acidic or basic a solution is.
It ranges from 0 to 14, and each number tells us something important about the concentration of H⁺ ions (Hydrogen ions) in the solution.
Full Form of pH:
> pH = “potential of Hydrogen” or “power of Hydrogen”
The pH value tells us how strongly acidic or basic a substance is:
- More H⁺ ions → lower pH → more acidic
- More OH⁻ ions → higher pH → more basic (alkaline)
Visual Representation of pH Scale
| pH Value | Nature of Solution | Colour on Universal Indicator | Example Substances |
|---|---|---|---|
| 0 – 3 | Strongly Acidic | Red | Hydrochloric acid (HCl), Gastric juice |
| 4 – 6 | Weakly Acidic | Orange to Yellow | Vinegar, Lemon juice |
| 7 | Neutral | Green | Pure Water |
| 8 – 10 | Weakly Basic | Blue | Baking soda, Soap solution |
| 11 – 14 | Strongly Basic | Dark Blue to Violet | Sodium hydroxide (NaOH), Bleach |
Concept: Hydrogen Ion Concentration
The pH value is inversely related to H⁺ ion concentration:
- Every 1 unit change in pH means a 10-fold change in H⁺ concentration.
> Example: A solution with pH = 3 has 10 times more H⁺ ions than a solution with pH = 4.
That’s why acids with pH = 1 or 2 are very corrosive, like concentrated HCl or H₂SO₄.
Case Study: pH of Some Common Substances
| Substance | Nature | Approx. pH |
|---|---|---|
| Lemon Juice | Acidic | 2 – 3 |
| Vinegar | Acidic | 3 |
| Pure Water | Neutral | 7 |
| Baking Soda | Basic | 8 – 9 |
| Milk of Magnesia | Basic | 10 |
| Stomach acid (HCl) | Strong Acid | 1 – 2 |
| Toothpaste | Mild Base | 8 |
Remember: Our body fluids like blood have a pH of around 7.4 – slightly basic. Even a small change in blood pH can be fatal.
Why is pH Important in Daily Life?
1. Tooth Decay and pH
- Tooth enamel is made of calcium phosphate, which starts to corrode below pH 5.5
- That’s why sugary foods (which produce acids) can lower pH and cause cavities.
2. pH and Soil Health
- Some plants grow best in acidic soils, others in alkaline soils.
- Farmers use pH testing to decide whether to add lime (base) or manure (acidic) to balance the soil.
3. Shampoos and Soaps
- Our skin is naturally slightly acidic.
- Shampoos are formulated to maintain neutral or slightly acidic pH, so they don’t irritate the skin.
4. Industrial Waste and Rivers
- Industries must neutralize acidic/basic waste before releasing it into rivers.
- Fish and aquatic life can die if the pH becomes too acidic or basic.
5. Animal Stings
- Bee sting: injects acid → use baking soda (base) to neutralize
- Wasp sting: injects base → use vinegar (acid) to neutralize
Tip to Remember pH Scale
Think of a pH scale as a tug of war between acids and bases:
Acidic (0) ←←← 7 →→→ Basic (14)
More H⁺ More OH⁻
- Left side = Angry acids (Red-hot!)
- Right side = Calm bases (Cool-blue!)
- Middle = Peaceful water (Green-neutral)
Salts – The Hidden Compounds in Everyday Life
What Are Salts?
In simple terms, a salt is a neutral substance formed when an acid reacts with a base.
This reaction is called a Neutralisation Reaction, and the formula is:
Acid + Base → Salt + Water
Example:
HCl (Hydrochloric acid) + NaOH (Sodium hydroxide) → NaCl (Sodium chloride) + H₂O
Here, NaCl is the salt, which we also know as common salt – the one we sprinkle on our food!
Formation of Salts: The Reaction of Opposites
Salts are the peace treaties between the warring acids and bases. When the acidic hydrogen ions (H⁺) and basic hydroxide ions (OH⁻) neutralize each other, they create:
- A Salt (from the leftover ions of acid and base)
- Water
This makes the reaction:
→ Exothermic (i.e., releases heat)
Types of Salts – More Than Just NaCl!
Although we mostly hear about table salt, there are many types of salts depending on the acid and base involved.
| Type of Salt | Made From | Example |
|---|---|---|
| Normal Salt | Complete neutralization | NaCl (Sodium chloride) |
| Acidic Salt | Strong acid + weak base | NH₄Cl (Ammonium chloride) |
| Basic Salt | Weak acid + strong base | Na₂CO₃ (Sodium carbonate) |
| Double Salt | Two different salts crystallized together | Mohr’s salt (FeSO₄.(NH₄)₂SO₄·6H₂O) |
| Mixed Salt | Two acidic or basic radicals | CaOClCl (Bleaching powder) |
Common Salt – More Than Just a Kitchen Item
Common Salt (Sodium Chloride – NaCl) is:
- Formed from: HCl (acid) + NaOH (base)
- White crystalline solid
- Essential for life (in blood, nerves, etc.)
- Used as raw material to manufacture many other compounds
It’s extracted from:
- Sea water
- Rock salt deposits (called Sendha namak)
The Salt Cycle – Chain Reactions of Chemistry
From common salt (NaCl), we can make:
| Product | Use |
|---|---|
| Sodium Hydroxide (NaOH) | Soap making, cleaning agents |
| Bleaching Powder (CaOCl₂) | Whitening clothes, disinfecting water |
| Baking Soda (NaHCO₃) | Cooking, baking, medicines |
| Washing Soda (Na₂CO₃) | Detergents, glass industry |
| Hydrochloric Acid (HCl) | Laboratory acid, digestion |
This is called the Salt Industry Cycle, and it shows how one simple salt can give rise to many useful compounds.
Creative Analogy: The Salt Kingdom
Imagine a kingdom called Saltland:
- Queen Acid brings H⁺ soldiers
- King Base brings OH⁻ soldiers
- They fight, but in the end, peace is signed – a baby is born called Salt, and peace is celebrated with Water!
Key Facts
- Salts may be acidic, basic, or neutral depending on the strength of parent acid and base.
- Salts are electrolytes, meaning they conduct electricity in solution.
- pH of salt solutions can vary:
- NaCl solution: Neutral (pH ~ 7)
- NH₄Cl solution: Acidic (pH < 7)
- Na₂CO₃ solution: Basic (pH > 7)
Summary
Salts are neutral substances formed by acid-base reactions. Common salt (NaCl) is the most familiar, but other salts like baking soda and washing soda are equally important. Salts play a big role in chemistry, daily life, and industry.
Important Salts and Their Uses
Why Are Salts So Important?
Salts are not just what we add to food for taste — they are essential building blocks in our homes, industries, and even inside our bodies! While common salt (NaCl) is the most famous, there are many other salts with very important and diverse uses.
Let’s explore the star salts featured in the chapter, their preparation, properties, and amazing roles in our daily lives.
1. Sodium Hydroxide (NaOH) – The Caustic Creator
How is it Made?
It is produced by the electrolysis of an aqueous solution of sodium chloride (brine). This is known as the Chlor-Alkali Process.
2NaCl (aq) + 2H₂O (l) → 2NaOH (aq) + Cl₂ (g) + H₂ (g)What Else is Produced?
- Chlorine gas (Cl₂) → Used for disinfectants and PVC.
- Hydrogen gas (H₂) → Used in fuel and making ammonia.
Uses of Sodium Hydroxide:
- Making soap and detergents
- In paper and textiles
- As a cleaning agent in drain cleaners
- In petroleum refining
Fact: Think of NaOH as the “Housekeeper” of Chemistry — always cleaning and helping other compounds get made!
2. Bleaching Powder (CaOCl₂) – The Fabric Whitener
How is it Made?
Bleaching powder is made by passing chlorine gas over dry slaked lime [Ca(OH)₂].
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂OUses of Bleaching Powder:
- Bleaching cotton and linen in textiles
- Disinfecting drinking water
- Used in laundries and paper industries
- Used in manufacturing chloroform
Tip: Bleaching powder is like a laundry wizard — removing stains, whitening cloth, and killing germs all in one magic puff!
3. Baking Soda (NaHCO₃) – The Kitchen Chemist
Chemical Name:
Sodium Hydrogen Carbonate
How is it Made?
Made using sodium chloride, water, carbon dioxide, and ammonia in the Solvay Process.
NaCl + H₂O + CO₂ + NH₃ → NaHCO₃ + NH₄ClUses of Baking Soda:
- As a baking agent – it releases CO₂ on heating, making food soft and fluffy.
- As an antacid – it neutralizes excess stomach acid.
- Used in fire extinguishers and cleaning.
Fact: Without NaHCO₃, your cake would be as flat as a dosa!
4. Washing Soda (Na₂CO₃·10H₂O) – The Laundry Hero
Chemical Name:
Sodium Carbonate Decahydrate
How is it Made?
By heating baking soda (NaHCO₃) strongly to form sodium carbonate, and then crystallizing it with water.
1. 2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O
2. Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂OUses of Washing Soda:
- Softening hard water
- Used in laundry as a cleaning agent
- In glass, soap, and paper industries
- Acts as a mild antiseptic
Visual: Washing soda is like a detergent warrior — battling hard water ions and leaving your clothes fresh and clean!
5. Plaster of Paris (CaSO₄·½H₂O) – The Sculptor’s Friend
How is it Made?
Made by heating gypsum (CaSO₄·2H₂O) to remove water.
CaSO₄·2H₂O (Gypsum) → CaSO₄·½H₂O (POP) + 1½H₂OUses of Plaster of Paris:
- For immobilizing broken bones (orthopedic uses)
- In making statues and decorative items
- For moulding and false ceilings
- In dentistry and sculpting
Analogy: POP is the "magic clay" that freezes beauty, art, or healing into shape in minutes.
Summary Table – Important Salts & Their Wonders
| Salt Name | Chemical Formula | Common Use |
|---|---|---|
| Sodium Hydroxide | NaOH | Soap making, paper, cleaners |
| Bleaching Powder | CaOCl₂ | Water treatment, whitening clothes |
| Baking Soda | NaHCO₃ | Baking, antacid, fire extinguisher |
| Washing Soda | Na₂CO₃·10H₂O | Water softening, detergent making |
| Plaster of Paris (POP) | CaSO₄·½H₂O | Moulds, casts, interior decoration |
Always remember:
- NaOH comes from electrolysis of brine.
- Bleaching powder is made using chlorine gas.
- Baking soda produces CO₂ on heating.
- Washing soda has 10 water molecules of crystallization.
- POP sets quickly with water but cannot be exposed to moisture.
