Pause and Ponder Questions Solved| Ch 5 Science Class 9

Pause and Ponder are some of the most important and conceptual questions that are given in the textbook.

So we have solved those questions and the answers are strictly based on NCERT textbook chapter 5. So that you wont get your marks deducted. “Pause and Ponder Questions Solved| Ch 5 Science Class 9“, is easy to read and learn and retain.

Related| Chapter 5 Notes And Questions Answers

Q1. A common talcum powder contains 4% m/m zinc oxide, which acts as an antiseptic. How much zinc oxide is present in 300 g of the talcum powder?

Answer:

4% m/m means 4 g of zinc oxide is present in every 100 g of powder.

So, in 300 g of powder:

$\text{Zinc oxide} = \frac{4}{100} \times 300 = \mathbf{12\ g}$ Ans

Q2. Your mother gives you a bottle of orange juice concentrate to mix with water. She asks you to mix two tablespoons of the concentrate with water in a glass tumbler. If each tablespoon measures 15 mL and you make 150 mL of juice per person, what is the % v/v of orange juice concentrate in the mixture?

Answer:

Volume of concentrate = 2 × 15 mL = 30 mL
Volume of solution (juice) = 150 mL

Q3. Vinegar contains 5% v/v acetic acid. Glacial acetic acid is 100% acetic acid. How would you make vinegar from glacial acetic acid?

Answer:

Take 5 mL of glacial acetic acid. Add water to it until the total volume becomes 100 mL.

This gives a 5% v/v acetic acid solution, which is vinegar. Ans

Q4. Refer to the solubility curves in Activity 5.2. If equal masses of hot, saturated solutions of compounds ‘A’ and ‘B’ are cooled from 80°C to 60°C, which solution is likely to deposit more solid?

Answer:

Compound B will deposit more solid.

Its solubility curve is much steeper than that of compound A. So, when the temperature drops, the solubility of B falls by a larger amount than that of A. This means more of compound B comes out of the solution as solid.

Q5. Will there be any change in the size of common salt crystals if the rate of evaporation is increased or decreased? Explain.

Answer:

Yes, the crystal size changes with the rate of evaporation.

• Fast evaporation: gives particles less time to arrange themselves. This forms smaller crystals.
• Slow evaporation gives particles more time to come together . This forms larger, crystals.

Q6. State whether the following statements are True or False. Correct the false ones.

(i) Salt can be separated from a salt solution by evaporation or distillation.
(ii) Distillation can be used for separation of two liquids even when these have the same
boiling point.
(iii) In paper chromatography, the solvent level should be above the sample spot at the
beginning of the experiment.
(iv) Evaporation and crystallization are the same processes

Answers:

(i) True

(ii) False
Distillation only works when the two liquids have a boiling point difference of at least about 25°C. If both liquids have the same boiling point, they vaporise together and cannot be separated this way.

(iii) False.
The solvent level should be below the sample spot at the start. If the spot itself gets dipped in the solvent, the sample will simply dissolve into the solvent instead of moving up the paper.

(iv) False
Evaporation removes the solvent completely, leaving behind the solute (for example, plain salt with no defined shape).

Crystallization is different. It forms a saturated solution and then cools it slowly. This lets pure, well-shaped crystals separate out, while some solution still remains.

Q7. Why do immiscible liquids form two separate layers in a separating funnel?

Answer:

Immiscible liquids do not mix with each other. They also have different densities.

So, the denser liquid settles at the bottom, and the lighter liquid floats on top, forming two clear layers.

Q8. Is sublimation different from evaporation? Justify.

Answer:

Yes, they are different. Sublimation starts from a solid, evaporation starts from a liquid.

• Sublimation: A solid changes directly into vapour, without turning into liquid first. This happens even below the substance’s melting point. Example: camphor.
• Evaporation: A liquid changes into vapour from its surface, below its boiling point.

Q9. Clouds are made up of tiny water droplets or ice crystals floating in the air. What type of mixture are clouds, and why?

Answer:

Clouds are a colloid.

The tiny water droplets or ice crystals (dispersed phase) stay evenly spread out in air (dispersion medium). They do not settle down like a suspension would. This matches how a colloid behaves.

Q10. Why do cities with a lot of smoke and dust in the air often look hazy?

Answer:

Smoke and dust particles in the air scatter light passing through them. This scattering is called the Tyndall effect.

Because of this scattering, the air looks hazy instead of clear.