Class 7 Science - CBSE
Exploring Substances: Acidic, Basic and Neutral
In this chapter, Class 7 students explore the chemical nature of various substances around us by classifying them into acids, bases, and salts. You will learn how to identify these substances using natural indicators like litmus, turmeric, and China rose. The chapter also covers the crucial concept of neutralization reactions, explaining how acids and bases cancel each other out. This topic is essential for CBSE exams as it builds the foundational chemical knowledge required for higher classes and frequently features in application-based questions, conceptual queries, and practical-based multiple-choice questions.
Start Learning FreeKey Concepts
Acids
Substances that taste sour and turn blue litmus red. They contain hydrogen ions and are found in citrus fruits like lemons and oranges.
Bases
Substances that are bitter in touch and soapy to touch, turning red litmus blue. Examples include baking soda, soap, and lime water.
Indicators
Special substances used to test whether a given substance is acidic or basic by changing their color in different mediums.
Neutral Substances
Substances that are neither acidic nor basic, such as distilled water, and do not change the color of litmus paper.
Neutralization Reaction
A reaction between an acid and a base that produces salt, water, and heat energy, effectively canceling out each other's properties.
Important Formulas
Board Exam Info
In CBSE Class 7 Science exams, this chapter typically carries around 5 to 8 marks. Common question types include defining neutralization, identifying color changes in indicators, explaining real-life applications like treating ant bites or soil treatment, and short conceptual reasons.
Frequently Asked Questions
Why does turmeric stain on clothes turn reddish-brown when washed with soap?
Turmeric is a natural indicator. Soap is basic in nature, and indicators turn red or reddish-brown when they come in contact with a base.
What happens during a neutralization reaction?
Why do we take an antacid when suffering from acidity?
Our stomach produces hydrochloric acid for digestion, but excess acid causes indigestion. An antacid contains a mild base like milk of magnesia that neutralizes the excess acid and provides relief.
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