CBSE Class 7 Science Notes Chapter 2 - Exploring Substances PDF Download
Neha Tanna12 Jun, 2026
Different substances around us have different properties and uses. These CBSE Class 7 Science Notes Chapter 2 explain acids, bases, neutral substances, indicators, and neutralization in a simple and easy-to-understand format.
The chapter also covers the pH scale, acid rain, and the use of neutralization in daily life. These Exploring Substances notes help students revise important concepts quickly and prepare better for exams.
Exploring Substances Class 7 Notes
This part builds on basic ideas, laying the foundation for your Exploring Substances Class 7 notes. Acids are common in food and other items.
What Are Acids?
Acids are chemical substances. They have a sour taste. Many foods get their sourness from acids. Examples include lemons, curd, and oranges. Acidic substances contain acid.
Natural Acids
Some acids occur naturally. We find them in fruits and other organic sources.
|
Name of Acid |
Found In |
|---|---|
|
Acetic Acid |
Vinegar |
|
Formic Acid |
Ant's Sting |
|
Citric Acid |
Citrus fruits (oranges, lemons) |
|
Lactic Acid |
Curd |
|
Oxalic Acid |
Spinach |
|
Ascorbic Acid (Vitamin C) |
Amla, citrus fruits |
|
Tartaric Acid |
Tamarind, grapes, unripe mangoes |
Exploring Substances Notes: Bases and Neutral Substances
Continuing our journey, this section explains bases and neutral substances, expanding on your Exploring Substances notes.
What Are Bases?
Bases are chemical substances. They taste bitter and feel soapy. Bleach, ammonia, and soap contain bases. ases are also called alkaline. Basic substances contain a base.
Common Bases
Bases are found in many household products.
|
Name of Base |
Found In |
|---|---|
|
Calcium Hydroxide |
Limewater |
|
Ammonium Hydroxide |
Window cleaner |
|
Sodium Hydroxide |
Soap |
|
Potassium Hydroxide |
Soap |
|
Magnesium Hydroxide |
Milk of Magnesia |
Neutral Substances
A neutral substance is neither acidic nor basic. It has a balanced nature. Water is a common example.
Indicators and Their Use
We cannot taste every substance to find its nature. Indicators help us identify acids and bases safely. This is a vital concept in Exploring Substances Class 7 Science notes.
What Are Indicators?
An indicator is a substance. It changes color in acidic or basic solutions. This color change shows if a substance is acidic or basic. Natural indicators come from nature. Turmeric, China rose petals, and litmus are examples.
Types of Natural Indicators
-
Litmus: This natural indicator comes from lichens. It is available as a solution or paper strips (red and blue). Blue litmus turns red in acid. Red litmus turns blue in base.
-
Turmeric: Turmeric powder can be mixed with water to form a paste. This paste is spread on blotting paper to make turmeric paper. Turmeric paper turns red in a basic solution but shows no change in an acidic solution.
-
China Rose: Petals of China rose are soaked in warm water. This makes a colored solution. This solution turns dark pink (magenta) in acid. It turns green in a basic solution.
Indicator Effects
|
S.No. |
Name of Substance |
Effect on Litmus Paper |
Effect on Turmeric Paper |
Effect on China Rose Solution |
|---|---|---|---|---|
|
1. |
Hydrochloric Acid |
Blue litmus turns red |
No change |
Turns dark pink |
|
2. |
Sulphuric Acid |
Blue litmus turns red |
No change |
Turns dark pink |
|
3. |
Nitric Acid |
Blue litmus turns red |
No change |
Turns dark pink |
|
4. |
Acetic Acid |
Blue litmus turns red |
No change |
Turns dark pink |
|
5. |
Sodium Hydroxide |
Red litmus turns blue |
Turns red |
Turns green |
|
6. |
Ammonium Hydroxide |
Red litmus turns blue |
Turns red |
Turns green |
|
7. |
Calcium Hydroxide |
Red litmus turns blue |
Turns red |
Turns green |
pH Scale and Acid Rain
The pH scale measures how acidic or basic a substance is.
pH Scale
The pH value ranges from 1 to 14. A pH of 1 means highly acidic. A pH of 14 means highly basic. A pH of 7 is neutral. pH strips or solutions help determine the pH value. Acids are reactive. They are stored in glass containers, not metal ones, to prevent reactions.
Acid Rain
Acid rain occurs when rainwater has increased amounts of acid. Air pollutants like nitrogen dioxide, carbon dioxide, and sulfur dioxide cause it. These gases mix with rainwater. They form nitric acid, sulfuric acid, and carbonic acid. Acid rain harms plants, animals, and buildings.
Neutralization and Daily Life
Neutralization is a key chemical process.
What is Neutralization?
Neutralization is a reaction. An acid and a base mix. They neutralize each other's effects. This process forms a product called a salt. Salts can be acidic, basic, or neutral. Neutralization also releases heat, raising the mixture's temperature. Phenolphthalein solution is a synthetic indicator for neutralization. It is pink in the base and colorless in acid.
Formation of Salt
The general reaction is:
Neutralization in Everyday Life
-
Indigestion: Our stomach makes hydrochloric acid for digestion. Too much acid causes indigestion. Antacids, which are basic, neutralize this excess acid. Milk of magnesia is a common antacid.
-
Ant Bite: An ant bite injects formic acid into the skin. This causes irritation. Basic substances like baking soda or calamine solution neutralize the acid.
-
Soil Treatment: Plants need neutral soil. Chemical fertilizers can make soil acidic. Quicklime (calcium oxide) or slaked lime (calcium hydroxide) treats acidic soil. Adding organic matter treats basic soil.
-
Factory Wastes: Factory waste is often acidic. It cannot be dumped directly. Bases are added to it before disposal. This protects aquatic life in rivers and streams.
Exploring Substances Class 7 Science Notes PDF
Students can download the Exploring Substances Class 7 Science Notes PDF for quick revision and easy learning. It covers important topics like acids, bases, indicators, pH scale, acid rain, and neutralization in a simple format. These CBSE Class 7 Science Notes Chapter 2 PDF notes are useful for exam preparation, homework, and last-minute revision.
Exploring Substances Class 7 Science Notes PDF
How to Use Exploring Substances Class 7 Notes for Exam Preparation
Exploring Substances Class 7 notes help students revise important concepts quickly and understand the chapter more clearly. These notes are useful for remembering definitions, reactions, and examples before exams.
-
Revise acids, bases, and indicators regularly.
-
Learn examples of natural acids and bases.
-
Practice pH scale and neutralization concepts.
-
Study indicator color changes carefully.
-
Use the notes for quick revision before tests and exams.
CBSE Class 7 Science Notes Chapter 2 FAQs
What are indicators used for?
Name two natural indicators.
What is a neutralization reaction?
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