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Class 7 Science NCERT Solutions and Notes- Acid

Class 7 Science NCERT Solutions and Notes- Acid,7th class science,NCERT Solutions for Class 7th Science

Class 7 Science NCERT Solutions and Notes- Acid

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In this article, we will discuss the topic of Class 7 Science. We will discuss ‘Acid, Base, and Salt’.

Substances are divided into Acid, Base, and Salt.

ACID: The word Acid derives from Latin word ‘ACERE’ which means sour. Acid is sour in taste.Acid containing substances has sour in taste and the substance that sour in taste is called Acidic. The chemical nature of these substances is known as Acidic nature. For example – curd,orange juice,lemon, pickles, vinegar, etc.

BASE: Base is bitter in taste. Base containing substances has bitter in taste. The chemical nature of substances that contain base is known as BASE For example; baking soda, soap or soap solution, washing soda, etc.

INDICATOR: It is not practical to taste every substance to check whether a substance is acidic or basic. Special kind of substance is used to test the chemical nature (acidic or basic) of the substance is known as INDICATOR.The Indicator is a substance that shows the chemical nature (acidic or basic) of a substance by a change in its color.

Types of Indicator: There are two types of indicators:

Natural Indicator: Indicators that are derived from naturally occurring substance are called NATURAL INDICATORS. For example; turmeric, China rose,litmus, etc.

Synthetic Indicator/ Artifical indicators: Indicators that are prepared in the laboratory are known as SYNTHETIC INDICATORS. For example; methyl orange,phenolphthalein, etc.

Watch animated and virtual experiments for how indicators work? Click NCERT solutions for Class 7th Science.


Litmus: Litmus is extracted from Lichens. A lichen is a composite organism and Litmus is extracted from it. Lichens consist of algae and fungi living in a symbiotic relationship.

Litmus is a purple colored liquid in distilled water. Litmus appears in the form of strips of two colors. One is called red litmus paper and another is called blue litmus paper.

Both Litmus liquid and paper are used to identify the acidic or basic nature of a substance.

Use of Litmus paper to detect acid or base.

Acid– When blue litmus paper dipped in theacidic solution, the color of the litmus paper turns red.

Base- when the red color litmus paper dipped in a basic solution, the color of the litmus paper turns blue.

Turmeric: Turmeric is also used as a natural indicator. The color of the turmeric is yellow. When the Turmeric paper dipped into a basic solution, the paper turns red and does not change its color when it is dipped into acid.

China Rose: Next natural indicator is China rose. When China rose solution react with acid it turns into dark pink (magenta) color and reacts with the base it turns in green color.

For Synthetic indicators, visit online Class 7 Science

Acid Rain: Carbon dioxide, nitrogen dioxide, and sulphur dioxide, which is released from factory chimneys and vehicle mix with droplets of rain and turn the rain water acidic. When this acidic rain water falls over the earth, it is called acid rain. Acid rain is dangerous, it is harmful to plants and animals and also damages the buildings.

Many historical buildings like Taj Mahal, Red Fort, etc. is under threat because of acid rain.

Characteristics of Acid:

  • Sour in taste.
  • Turns blue litmus paper red.
  • Turns the solution of China rose to dark pink color (magenta).

Characteristics of Base:

  • Bitter in taste.
  • Turns red litmus paper blue.
  • Turns solution of China rose into the green.
  • Turns turmeric paper to the red.

Salt and Nuterialisation will discuss in the next article. For videos on the same, click on 7th Class Science.

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October 11, 2017

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