Have you ever thought about how toothpaste protects your teeth, lemon tastes sour, or antacids relieve stomach acidity? All of these are connected to acids, bases, and salts. This chapter is one of the most important and high-scoring chapters in CBSE Class 10 Science. If students understand the concepts clearly, they can easily score good marks in board exams.
What are Acids?
Acids are substances that release Hydrogen ions (H⁺) when dissolved in water.
Properties of Acids
Sour in taste
Turn blue litmus paper red
React with metals to produce hydrogen gas
Have pH less than 7
Conduct electricity in aqueous solution
Examples of Acids
Hydrochloric Acid (HCl)—Present in stomach, helps digestion
Sulphuric Acid (H₂SO₄) – Used in car batteries
Nitric Acid (HNO₃)—Used in fertilizers
Acetic Acid (CH₃COOH) – Found in vinegar
What are bases?
Bases are substances that produce hydroxide ions (OH⁻) in water.
Note:A base that dissolves in water is called an Alkali.
Properties of Bases
Bitter in taste
Slippery to touch
Turn red litmus paper blue
Have pH greater than 7
Neutralize acids
Examples of Bases
Sodium Hydroxide (NaOH)—Used in soap making
Calcium Hydroxide [Ca(OH)₂] – Used in whitewashing
Magnesium Hydroxide – Used as antacid
Ammonium Hydroxide – Used in cleaning liquids
Indicators
Indicators are substances that show whether a solution is acidic or basic by changing color.
Natural Indicators
Litmus – Acid turns it red, base turns it blue
Turmeric – Turns reddish-brown in base
China Rose – Acid turns it pink, base turns it green
Synthetic Indicators
Phenolphthalein – Colorless in acid, pink in base
Methyl Orange – Red in acid, yellow in base
Olfactory Indicators
These indicators change smell in acidic or basic mediums.
Examples:
Onion
Vanilla
Clove oil
In bases, their smell becomes faint or disappears.
pH Scale
The pH scale tells how acidic or basic a solution is.
0 \leq pH \leq 14
pH < 7 → Acidic
pH = 7 → Neutral
pH > 7 → Basic
Importance of pH
Stomach acid for digestion has pH around 1–2
Tooth decay starts below pH 5.5
Farmers add lime to acidic soil
Sudden pH changes harm aquatic life
Important Reactions of Acids and Bases
1. Acid + Metal → Salt + Hydrogen Gas
Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2\uparrow
Hydrogen gas burns with a pop sound.
2. Acid + Carbonate → Salt + Water + Carbon Dioxide
Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2\uparrow
Carbon dioxide turns lime water milky.
3. Neutralization Reaction
HCl + NaOH \rightarrow NaCl + H_2O
Acid reacts with base to form salt and water.
4. Base + Non-Metal Oxide
Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O
Lime water turns milky.
What are salts?
Salts are compounds formed when acids react with bases.
Examples
Strong Acid + Strong Base → Neutral Salt (NaCl)
Strong Acid + Weak Base → Acidic Salt (NH₄Cl)
Weak Acid + Strong Base → Basic Salt (Na₂CO₃)
Important Salts for Exams
Common Salt (NaCl)
Used in food preservation
Raw material for many sodium compounds
Washing Soda (Na₂CO₃·10H₂O)
Cleaning agent
Softens hard water
Used in glass and soap industry
Baking Soda (NaHCO₃)
Used in baking powder
Used as antacid
Used in fire extinguishers
Bleaching Powder (CaOCl₂)
Disinfects drinking water
Used for bleaching clothes
Plaster of Paris (CaSO₄·½H₂O)
Used in making casts for fractured bones
Used for decorative items
Caustic Soda (NaOH)
Used in soap, paper and textile industries
Prepared by chlor-alkali process
Quick Revision Points
Acids release H⁺ ions
Bases release OH⁻ ions
pH less than 7 means acid
pH more than 7 means base
Acid + Base gives Salt + Water
Indicators help identify acids and bCBSE Class 10 Science: Acids, Bases and Salts Notes (100% Original)
Have you ever thought about how toothpaste protects your teeth, lemon tastes sour, or antacids relieve stomach acidity? All of these are connected to Acids, Bases and Salts. This chapter is one of the most important and high-scoring chapters in CBSE Class 10 Science. If students understand the concepts clearly, they can easily score good marks in board exams.
What are Acids?
Acids are substances that release Hydrogen ions (H⁺) when dissolved in water.
Properties of Acids
Sour in taste
Turn blue litmus paper red
React with metals to produce hydrogen gas
Have pH less than 7
Conduct electricity in aqueous solution
Examples of Acids
Hydrochloric Acid (HCl)—Present in stomach, helps digestion
Sulphuric Acid (H₂SO₄) – Used in car batteries
Nitric Acid (HNO₃)—Used in fertilizers
Acetic Acid (CH₃COOH) – Found in vinegar
What are bases?
Bases are substances that produce hydroxide ions (OH⁻) in water.
Note:
A base that dissolves in water is called an Alkali.
Properties of Bases
Bitter in taste
Slippery to touch
Turn red litmus paper blue
Have pH greater than 7
Neutralize acids
Examples of Bases
Sodium Hydroxide (NaOH)—Used in soap making
Calcium Hydroxide [Ca(OH)₂] – Used in whitewashing
Magnesium Hydroxide – Used as antacid
Ammonium Hydroxide – Used in cleaning liquids
Indicators
Indicators are substances that show whether a solution is acidic or basic by changing color.
Natural Indicators
Litmus – Acid turns it red; base turns it blue
Turmeric – Turns reddish-brown in base
China Rose – Acid turns it pink; base turns it green
Synthetic Indicators
Phenolphthalein—Colorless in acid, pink in base
Methyl Orange—Red in acid, yellow in base
Olfactory Indicators
These indicators change smell in acidic or basic medium.
Examples:
Onion
Vanilla
Clove oil
In bases, their smell becomes faint or disappears.
pH Scale
The pH scale tells how acidic or basic a solution is.
0 \leq pH \leq 14
pH < 7 → Acidic
pH = 7 → Neutral
pH > 7 → Basic
Importance of pH
Stomach acid for digestion has pH around 1–2
Tooth decay starts below pH 5.5
Farmers add lime to acidic soil
Sudden pH change harms aquatic life
Important Reactions of Acids and Bases
1. Acid + Metal → Salt + Hydrogen Gas
Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2\uparrow
Hydrogen gas burns with a pop sound.
2. Acid + Carbonate → Salt + Water + Carbon Dioxide
Na_2CO_3 + 2HCl \ rightarrow 2NaCl + H_2O + CO_2\uparrow
Quick Revision Points
Acids release H⁺ ions
Bases release OH⁻ ions
pH less than 7 means acid
pH more than 7 means base
Acid + Base gives Salt + Water
Indicators help identify acids and bases
Conclusion
Acids, bases, and salts are an important chapter of chemistry and very useful in daily life. If you understand the pH scale, indicators, and reactions properly, this chapter becomes easy and highly scoring for CBSE Class 10 board exams.