04. Acids, Bases and Salts Class 7 Science NCERT Notes for Chapter 3 CBSE
Welcome to Acids, Bases and Salts Class 7 Science NCERT Notes for Chapter 3 CBSE
Exam Notes: Acids, Bases, and Salts
Introduction
In this article, we will delve into the fascinating world of Acids, Bases, and Salts. We encounter various substances in our daily life, and they often have distinct tastes. Let’s explore these tastes and understand the chemical nature behind them.
Substances and Their Tastes
Table 4.1 provides an overview of different edible substances and their tastes. It’s essential to note these taste differences for better understanding.
Table 4.1
| Substance | Taste |
|---|---|
| Lemon juice | Sour (Acid) |
| Orange juice | Sour (Acid) |
| Vinegar | Sour (Acid) |
| Curd | Sour (Acid) |
| Tamarind (imli) | Sour (Acid) |
| Sugar | Sweet |
| Common salt | Salty |
| Amla | Sour (Acid) |
| Baking soda | Bitter, Soapy (Base) |
| Grapes | Sweet |
| Unripe mango | Sour (Acid) |
| Cucumber | Any Other |
Understanding Acids
4.1 Acids and Bases
Curd, lemon juice, orange juice, and vinegar taste sour because they contain acids. Acids are characterized by their acidic nature, deriving their name from the Latin word “acere,” meaning sour. These acids are natural.
Bases
Not all substances taste sour. For instance, baking soda is bitter and feels soapy when touched. Such substances are known as bases, and their nature is considered basic.
Testing for Acidity or Basicity
To determine whether a substance is acidic or basic, we use special substances called indicators. These indicators change color when added to acidic or basic solutions. Turmeric, litmus, China rose petals (Gudhal), etc., are examples of naturally occurring indicators.
CAUTION: Never taste or touch unknown substances without proper guidance.
Natural Indicators
Litmus: A Natural Dye
Litmus, extracted from lichens, is a commonly used natural indicator. It’s mauve (purple) in distilled water, turns red in acidic solutions, and blue in basic solutions. Litmus is available as red and blue litmus paper.
Acid: A substance with a sour taste that turns blue litmus paper red.
Base: A substance with a bitter taste and soapy feel that turns red litmus paper blue.
Turmeric as an Indicator
Turmeric, when used as an indicator, can be prepared by making a paste with water and creating strips of yellow paper. It’s used to test for acidity or basicity in substances.
Indicator: A substance that changes color when added to acidic or basic solutions.
China Rose as Indicator
China rose petals can also serve as indicators. They turn acidic solutions dark pink (magenta) and basic solutions green.
Neutralization
4.3 Neutralization
When acids and bases are mixed in suitable amounts, they neutralize each other’s effects. This results in a solution that is neither acidic nor basic, producing salt and water with the release of heat.
Example Reaction:
Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + Water (H2O)
Applications in Everyday Life
- Indigestion: Antacids, like milk of magnesia (containing magnesium hydroxide), neutralize excessive stomach acid to relieve indigestion.
Antacid: A substance that counteracts excess stomach acid.
- Ant Bites: Formic acid from ant bites can be neutralized by applying moist baking soda (sodium hydrogencarbonate) or calamine solution, which contains zinc carbonate.
- Soil Treatment: Soil is treated with bases like quick lime (calcium oxide) to neutralize acidity or organic matter to counteract alkalinity for optimal plant growth.
- Factory Wastes: Industrial waste containing acids is neutralized by adding basic substances before disposal to prevent harm to the environment.
Conclusion
Understanding acids, bases, and salts is essential as they play a vital role in our daily lives. By using indicators and practicing caution, we can identify and manage these substances effectively.
Keywords
Important keywords and their definitions for – Acids Bases and Salts Class 7
- Acid: A substance with a sour taste that turns blue litmus paper red.
- Base: A substance with a bitter taste and soapy feel that turns red litmus paper blue.
- Indicator: A substance that changes color when added to acidic or basic solutions.
- Neutralization: The process where acids and bases neutralize each other, forming salt and water with the release of heat.
- Antacid: A substance that counteracts excess stomach acid.
Frequently Asked Questions (FAQs)
FAQ for Acids Bases and Salts Class 7 chapter 4
1. What are some common indicators for testing acids and bases?
- Common indicators include litmus paper (red and blue), turmeric, and China rose petals.
2. Why should we not taste or touch unknown substances without guidance?
- Unknown substances can be harmful, so it’s essential to exercise caution and use proper testing methods.
3. What happens when acids and bases are mixed in the right proportions?
- They neutralize each other, resulting in a solution that is neither acidic nor basic, along with the release of heat.
4. How are antacids used to relieve indigestion?
- Antacids, such as milk of magnesia, neutralize excessive stomach acid, providing relief from indigestion.
5. What is the significance of indicators in testing for acidity or basicity?
- Indicators change color when added to acidic or basic solutions, allowing us to identify the nature of substances.
6. Can you provide examples of natural acids and bases?
- Natural acids include citric acid (found in citrus fruits), acetic acid (in vinegar), and lactic acid (in curd). Natural bases include calcium hydroxide (in lime water) and sodium hydroxide (in soap).
7. How does neutralization occur in soil treatment?
- Soil treatment involves adding substances like quick lime to neutralize acidic soil or organic matter to neutralize basic soil, ensuring optimal conditions for plant growth.
8. What are the environmental consequences of untreated factory wastes containing acids?
- Factory wastes with acids can harm the environment, leading to damage to aquatic ecosystems and soil. Neutralizing such wastes before disposal is crucial.
9. What are some uses of turmeric as an indicator?
- Turmeric can be used to test for acidity or basicity in various substances. It’s also used for creative purposes, such as making greeting cards.
This was the end of Acids, Bases and Salts Class 7 Science NCERT Notes for Chapter 3 CBSE
For more information, refer to NCERT SOLUTIONS, NCERT NOTES, and NCERT BOOKS .
