Exploring Substances Acidic Basic and Neutral Class 7 Notes

Exploring Substances Acidic Basic and Neutral Class 7 Notes

Exploring Substances Acidic Basic and Neutral Class 7 Notes

1. Activity: A general engagement or series of actions performed by an individual or group.
2. Laboratory: A place for experimental study, testing and analysis about science.
3. Lime water: Solution of calcium hydroxide in water.
4. Chuna: Calcium oxide.
5. Baking soda: Sodium bicarbonate.
6. Abundant: Available in large quantities.
7. Applauded: Show strong approval of a person; praise.
8. Blindfolded: To cover the eyes so that someone cannot see.
9. Acidic Solution: A solution that turns blue litmus paper to red.
10. Basic solution: A solution that turns red litmus paper to blue.

Acids, Bases, and Indicators

Acidic Substances: Sour in taste, turn blue litmus paper to red, (e.g., Lemon juice, amla juice, tamarind water, and vinegar).

Basic Substances: Bitter in taste and soapy in touch, turn red litmus paper to blue, (e.g., soap solution, baking soda solution, lime water, and washing powder solution)

Neutral Substances: Do not change the colour of either litmus paper, (e.g., tap water, sugar solution, and salt solution).

Indicators: Substances that show different colours in acids and bases, Litmus is an acid-base indicator.

Litmus as an Indicator

A natural indicator obtained from lichens, available in two colours—blue and red commonly used in labs and tests.

1. Blue Litmus: Turns red in acid, remains blue in base.
2. Red Litmus: Turns blue in base, remains red in acid.

Red Rose as an Indicator

Petal extract of red rose used as a natural indicator.

1. In Acid: Shows a certain colour (often red/pink)
2. In Base: Turn colour to greenish/blue.

Turmeric as an Indicator

Bright yellow in colour, often used in home as spice

1. In Acid: Remains yellow.
2. In Base: Turns reddish-brown.

Olfactory indicators:

1. Odours change in an acidic or basic medium. (e.g., chopped onions)

What Happens When Acidic Substances Mix with Basic Substances?

1. A chemical reaction takes place called neutralisation produces salt and water.
2. Acid + Base → Salt + Water + Heat

Neutralisation in Daily Life

1. Indigestion: Antacids (base) cold milk neutralise excess stomach acid.
2. Wasp/Bee Stings: Treated with a base (like moist baking soda for bee sting).
3. Soil Treatment: Excess acid neutralised using quicklime or slaked lime if soil is basic.
4. Factory Wastes: Acidic wastes are neutralized by adding base before disposal into lakes or river.