Class 7 Science - PUNJAB
Exploring Substances: Acidic, Basic and Neutral
In the chapter 'Exploring Substances: Acidic, Basic and Neutral', Class 7 Punjab (PSEB) students learn to identify different materials based on their chemical nature. The chapter covers natural indicators like turmeric, litmus, and China rose to test substances safely. Students explore how acids taste sour and turn blue litmus red, while bases are bitter, soapy to touch, and turn red litmus blue. Neutral substances show no change in indicator color. Understanding this chapter is crucial for board exam preparation as it forms the foundation of chemistry and frequently appears in PSEB question papers through practical-based applications and conceptual queries.
Start Learning FreeKey Concepts
Acids
Substances that taste sour and turn blue litmus paper to red. Examples include lemon juice, vinegar, and hydrochloric acid.
Bases
Substances that taste bitter, feel soapy to the touch, and turn red litmus paper to blue. Examples include baking soda, soap, and lime water.
Indicators
Special chemical substances used to test whether a given substance is acidic or basic by changing their color.
Neutralization
The reaction between an acid and a base resulting in the formation of salt and water, releasing heat in the process.
Neutral Substances
Substances that are neither acidic nor basic and do not change the color of red or blue litmus paper, such as pure water.
Important Formulas
Board Exam Info
In the Punjab (PSEB) Class 7 Science examinations, this chapter typically carries around 4 to 6 marks. Common question types include short answer questions on definitions of indicators, fill-in-the-blanks regarding color changes, and application-based questions like treating ant stings or soil treatment.
Frequently Asked Questions
What is the natural color of litmus paper?
Litmus is extracted from lichens and its natural color is purple.
Why does an ant sting cause pain and how is it cured?
An ant sting injects formic acid into the skin, causing pain. It is cured by rubbing moist baking soda (a base) which neutralizes the acid.
Are all substances safe to taste to check if they are acidic or basic?
No, many laboratory acids and bases are corrosive and harmful to the skin and body. We must always use indicators to test them.
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