Introduction
Chapter 2 of Class 10 Science is one of the most important chapters for board exams. It covers the properties, reactions, and uses of Acids, Bases, and Salts in our daily life. Let’s understand this chapter in a simple and easy way!
What are Acids?
Acids are substances that taste sour and turn blue litmus paper red. They release hydrogen ions (H⁺) when dissolved in water. Common examples include:
- Hydrochloric Acid (HCl) – found in our stomach
- Sulphuric Acid (H₂SO₄) – used in car batteries
- Acetic Acid (CH₃COOH) – found in vinegar
- Citric Acid – found in lemons and oranges
What are Bases?
Bases are substances that taste bitter, feel slippery, and turn red litmus paper blue. They release hydroxide ions (OH⁻) in water. Common examples include:
- Sodium Hydroxide (NaOH) – used in soap making
- Calcium Hydroxide Ca(OH)₂ – used in whitewashing
- Magnesium Hydroxide Mg(OH)₂ – used in antacids
What are Salts?
When an acid reacts with a base, a salt and water are formed. This reaction is called a Neutralisation Reaction. Example: HCl + NaOH → NaCl + H₂O. Common salts and their uses:
- Common Salt (NaCl) – used in cooking and food preservation
- Baking Soda (NaHCO₃) – used in cooking and as an antacid
- Washing Soda (Na₂CO₃) – used in cleaning
- Bleaching Powder – used for disinfecting water
pH Scale
The pH scale measures how acidic or basic a solution is. It ranges from 0 to 14:
- pH less than 7 = Acidic
- pH equal to 7 = Neutral
- pH greater than 7 = Basic/Alkaline
Our body works best at a specific pH. For example, blood has a pH of about 7.4.
Important Reactions to Remember
- Acid + Metal → Salt + Hydrogen gas
- Acid + Metal Oxide → Salt + Water
- Acid + Base → Salt + Water (Neutralisation)
- Acid + Metal Carbonate → Salt + Water + CO₂
Key Questions for Board Exam
Q1. What happens when an acid is mixed with a base?
Ans: A neutralisation reaction takes place, forming salt and water.
Q2. Why does tooth decay occur?
Ans: Bacteria in our mouth produce acids by breaking down sugar. These acids lower the pH in the mouth and damage tooth enamel.
Q3. What is the use of baking soda?
Ans: Baking soda (NaHCO₃) is used in cooking as a leavening agent, and also as an antacid to neutralise excess acid in the stomach.
Q4. Why do we use indicators?
Ans: Indicators like litmus, phenolphthalein, and methyl orange help us identify whether a substance is acidic, basic, or neutral.
Quick Revision Tips
- Remember: Acids are sour, Bases are bitter
- pH less than 7 = Acid, pH more than 7 = Base
- Neutralisation = Acid + Base → Salt + Water