Question Bank — The Amazing World of Solutes, Solvents, and Solutions

Section A — MCQs (10 questions, 1 mark each)

1. Which of the following is an example of a uniform mixture?
   (a) Sand mixed with water
   (b) Sawdust floating on water
   (c) Sugar dissolved completely in water
   (d) Chalk powder settling at the bottom of water

2. In a solution prepared by dissolving a solid in a liquid, the component present in smaller quantity is called:
   (a) Solvent
   (b) Solute
   (c) Saturated solution
   (d) Concentrated solution

3. Assertion (A): A saturated solution of salt in water at 30 °C becomes unsaturated when heated to 60 °C.
   Reason (R): Solubility of most solid solutes increases with rise in temperature.
   (a) Both A and R are true and R is the correct explanation of A.
   (b) Both A and R are true but R is not the correct explanation of A.
   (c) A is true but R is false.
   (d) A is false but R is true.

4. The solubility of oxygen gas in water:
   (a) Increases with increase in temperature
   (b) Decreases with increase in temperature
   (c) Remains unchanged with temperature
   (d) First increases then decreases

5. Density of a substance is calculated by the formula:
   (a) Volume/Mass
   (b) Mass/Volume
   (c) Mass × Volume
   (d) Volume × Mass

6. Assertion (A): Ice floats on water even though both are made of the same substance.
   Reason (R): Density of ice is less than density of liquid water at 0 °C.
   (a) Both A and R are true and R is the correct explanation of A.
   (b) Both A and R are true but R is not the correct explanation of A.
   (c) A is true but R is false.
   (d) A is false but R is true.

7. When a stone is lowered into a measuring cylinder containing water, the rise in water level gives:
   (a) Mass of the stone
   (b) Volume of the stone
   (c) Density of water
   (d) Solubility of the stone

8. A solution that contains less amount of solute compared to another solution of the same solvent at the same temperature is called:
   (a) Saturated
   (b) Unsaturated
   (c) Concentrated
   (d) Dilute

9. Which of the following will float on water?
   (a) An iron nail (density 7.8 g/cm³)
   (b) A wooden block (density 0.7 g/cm³)
   (c) A stone (density 2.5 g/cm³)
   (d) An aluminium block (density 2.7 g/cm³)

10. The curved surface formed by water in a narrow measuring cylinder is called:
    (a) Meniscus
    (b) Solute
    (c) Solvent
    (d) Density

Section B — Very Short Answer (6 questions, 2 marks each)

1. Define solubility of a solute. Give its unit as used in the chapter.
2. Distinguish between a dilute solution and a concentrated solution.
3. What is the SI unit of density? How is it related to g/cm³?
4. Why does the water level rise when an irregular solid is immersed in a measuring cylinder?
5. State one difference between the solubility behaviour of solids and gases with rise in temperature.
6. What is relative density? Why is it a number without units?

Section C — Short Answer (5 questions, 3 marks each)

1. A solution of baking soda is prepared at room temperature. On heating the solution, more baking soda dissolves. Explain the observation with reference to saturated and unsaturated solutions.
2. Describe briefly how the volume of an irregular solid such as a key can be determined using a measuring cylinder. Why must the object be tied with a thread?
3. Explain why oxygen dissolved in water is important for aquatic life and how an increase in water temperature affects this.
4. A wooden log and an iron rod have the same volume. Which one will float in water and why? Relate your answer to the concept of density.
5. Why are measuring cylinders made narrow and tall rather than short and wide? How does this help in accurate measurement of volume?

Section D — Long Answer (3 questions, 5 marks each)

1. Draw a neat labelled diagram of the experimental setup used to study the effect of temperature on the solubility of baking soda in water. Label the beaker, thermometer, stirrer, tripod stand, wire gauze and spirit lamp. Describe the observations at 20 °C, 50 °C and 70 °C and state the conclusion.
2. Define density. Derive the relation Density = Mass/Volume. A stone has mass 27 g and volume 10 cm³. Calculate its density and compare it with water to predict whether it will sink or float.
3. What are uniform and non-uniform mixtures? Give two examples of each from daily life. Explain with reason why a mixture of sugar and salt in water is uniform while a mixture of sand and water is non-uniform.

Section E — Case/Source-Based (2 questions, 4 marks each)

Case 1

During summer, a student prepares ORS by dissolving one teaspoon each of sugar and salt in 200 mL water. He observes that every sip tastes the same. When he adds five more teaspoons of salt, some salt remains undissolved at the bottom.

(a) What type of mixture is the ORS solution? (1 mark)
(b) After adding extra salt, what kind of solution is formed? (1 mark)
(c) If the same solution is gently heated, what change in the undissolved salt is expected? (1 mark)
(d) Name the solute and solvent in the ORS. (1 mark)

Case 2

In cold hilly regions, a layer of ice forms on the surface of lakes in winter while water below remains liquid. Fish continue to survive in the water under the ice.

(a) Why does ice float on water? (1 mark)
(b) How does the density of water change from 4 °C to 0 °C? (1 mark)
(c) What would happen to aquatic life if ice sank instead of floating? (1 mark)
(d) Name the special property of water responsible for this behaviour. (1 mark)

Section F — HOTS and Application (4 questions, 3 marks each)

1. Predict-and-justify: What would happen to the solubility of oxygen in a pond if the water temperature rises from 15 °C to 35 °C during summer? Justify your answer.
2. Analyse an anomalous observation: In an experiment, a student finds that a saturated solution of a solid at 40 °C dissolves more solute when cooled to 20 °C. Is this observation expected? Analyse and give reason.
3. Apply to unfamiliar real-life situation: A ship made of steel (density much higher than water) floats easily on sea water. Using the concept of density, explain why this is possible even though a small steel nail sinks.
4. Compare two situations: Two identical bottles are filled with equal volumes of water at 20 °C and 80 °C respectively. Which bottle will be heavier? Justify by comparing the densities of water at the two temperatures.