Page 52 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

mixtures are also called solutions. For example, lemonade is a homogeneous mixture

of water, sugar and lemon.

Heterogeneous mixtures : These are the mixtures with non-uniform composition.
They show distinct physical boundaries for various constituents. For example, mixture

of oil and water. When we mix oil and water, oil floats on water and never dissolves
completely. We can see a distinct boundary between oil and water.

3. Give one reason to show that water is a compound and iron is an element.
Ans. Water is a compound because it consists of two different elements, hydrogen and

oxygen, chemically combined in a fixed ratio.

Iron is an element because it is made up of only one type of atom and cannot be
broken down two simpler substances by any chemical means.

4. What are alkalis? Give examples.
Ans. Alkalis are bases that are soluble in water. They produce hydroxide ions (OH ) when
–
dissolved in water. For example, sodium hydroxide (NaOH), potassium hydroxide
(KOH), calcium hydroxide [Ca(OH) ].
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5. Do both acids and bases change colour of all indicators?

Ans. No, acids and bases do not change the colour of all indicators in the same way.
Different indicators respond diffrently to acids and bases. For example:

• Litmus paper: Turns red in acids and blue in bases.
• Phenolphthalein : colourless in acid and pink in bases.

• Methyl Orange : red in acids and yellow in bases.
6. What should be added to the soil when it becomes too acidic and why?

Ans. When soil becomes too acidic, substances like lime (Remove space calcium carbonate)

or slaked lime (calcium hydroxide) should be added to it. These substances neutralize
the excess acidity and help balance the pH of the soil.

7. How do acids and bases play an important role in the process of digestion?
Ans. Acids and bases are essential for digestion. In the stomach, hydrochloric acid (HCl)

breaks down food and activates enzymes to digest proteins. This acidic environment
also helps kill bacteria. As food moves to the small intestine, a base from the pancreas

neutralizes the acidic chyme from the stomach, creating an optimal pH For enzymes
to further break down nutrients. This balance of acids and bases ensures efficient

digestion & absorption of nutrients in the body.
8. Write the general properties of salts.

Ans. Properties of salts :

• They are solid at room temperature.

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