Page 53 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

• Some salts are white solids, such as zinc chloride (ZnCl ), while others can be
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coloured. For example, copper sulphate (CuSO ) is a blue-coloured salt while
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ferrous sulphate (FeSO ) is a light green-coloured salt.
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• They are soluble in water.
• They have high melting points.

G. Long-answer questions.
1. Differentiate between strong acids and weak acids by giving examples.

Ans. Strong acids and weak acids differ primarily in their ability to dissociate in water and
release hydrogen ions (H ).
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Strong acids : Strong acids completely dissociate into ions in water, resulting in a
high concentration of H ions and a low pH. For example, hydrochloric acid (HCl),
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sulphuric acid (H SO ) & nitric acid (HNO ).
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Weak Acids : Weak acids partially dissociate into ions in water resulting in a lower

concentration of H ions & a less acidic solution compared to strong acids. For
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example, acetic acid (CH COOH), citric acid (found in citrus fruits) & carbonic acid
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(H CO ).
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2. You are provided with three solutions labelled as A, B and C. One of these contains an

acid, strong enough to burn. Another is a clear soapy solution, but will make you want
to throw up if consumed. The third is water, safe enough to be consumed. Keeping in

mind that you cannot taste anything, how will you separate the safe drinking water
from the rest of the liquid?

Ans. To differentiate safe drinking water from the other solutions in A, B and C without
relying on taste, pH testing is a reliable method. Safe drinking water typically has a

neutral pH of 7. Using pH paper, each solution can be tested by dipping the paper
into it and observing the colour change. The solution that remains netural, showing

a pH close to 7, is likely the safe drinking water.
In contrast, the solution containing acid will exhibit a very low pH value (below 3 for

strong acids like hydrochloric acid), indicating its acidic nature. The soapy solution,
on the other hand is likely to show a pH above 7, indicating basic nature.

3. What is acid rain? How is it formed? Mention three adverse effects of acid rain.
Ans. Acid rain :

Gaseous pollutants, such as sulphur dioxide and oxides of nitrogen present in the
air react with water and oxygen in the atmosphere to form sulphuric acid and nitric

acid, respectively. The biggest sources are coal-burning power plants, factories and
automobiles. These acids dissolve in rainwater and come down as acid rain. Acid rain

is unusually acidic and corrosive in nature.

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