The Amazing World of Solutes, Solvents, and Solutions — Mastery

Q1. Which of the following is the best example of a non-uniform mixture described in Chapter 9?

• A. Sugar dissolved in water
• B. Salt dissolved in water
• C. Sawdust mixed with water
• D. Air

Q2. A 'solution' is best described as

• A. any uniform or non-uniform mixture of two substances
• B. a non-uniform mixture of a solid and a liquid
• C. any liquid that contains some solid particles floating in it
• D. a uniform mixture formed when a solute dissolves in a solvent

Q3. Fig. 9.3 of Chapter 9 shows a magnified schematic of a solution. In the diagram, the small particles spread evenly throughout the liquid represent

• A. solvent particles
• B. solute particles evenly distributed in the solvent
• C. undissolved solid settling at the bottom
• D. dust particles suspended in air

Q4. A Class 8 student argues, 'In Gulab jamun chashni, since sugar is the larger amount, sugar must be the solvent and water the solute.' Which of the following is the best response a teacher can give, based on Chapter 9?

• A. The student is correct; the larger-amount substance is always the solvent.
• B. The student is wrong; both should be called solutes since neither dominates.
• C. The student is wrong; the textbook treats water as the solvent and sugar as the solute in this example.
• D. The student is partially correct; sugar is the solvent only above 100 °C.

Q5. In Activity 9.1, two glasses are prepared at the same temperature: Glass P has one spoon of salt dissolved in 100 mL water; Glass Q has two spoons of salt dissolved in 100 mL water. Compared with Glass Q, the solution in Glass P is

• A. more dilute
• B. more concentrated
• C. saturated
• D. non-uniform

Q6. Fill in the blanks based on Question 2(ii) of 'Keep the curiosity alive': 'The maximum amount of ___________ dissolved in ___________ at a particular temperature is called solubility at that temperature.'

• A. solute, solvent
• B. solvent, solute
• C. mixture, water
• D. concentration, density

Q7. Two convenience units used for the density of liquids in addition to the SI unit. They are

• A. g/L and kg/L
• B. g/mL and g/cm³
• C. g·m³ and kg·cm³
• D. mL/g and cm³/g

Q8. An object has a mass of 400 g and a volume of 40 cm³. Based on Question 7 of 'Keep the curiosity alive', its density is

• A. 0.1 g/cm³
• B. 1 g/cm³
• C. 100 g/cm³
• D. 10 g/cm³

Q9. Objects A and B are placed in a Class 8 lab. A has a mass of 200 g and a volume of 40 cm³; B has a mass of 240 g and a volume of 60 cm³. Which object is denser? (Question 9 of 'Keep the curiosity alive')

• A. A
• B. B
• C. Both have the same density
• D. Cannot be decided without temperature

Q10. In Activity 9.7, the initial volume of water in a measuring cylinder is 50 mL. When a stone is gently lowered into the water, the level rises to 55 mL. The volume of the stone is

• A. 50 cm³
• B. 55 cm³
• C. 5 cm³
• D. 105 cm³

Q11. The effect of pressure on density is

• A. large for gases, small for liquids and solids
• B. negligible for all three states
• C. large for solids and liquids, small for gases
• D. the same in all three states because pressure is uniform

Q12. While planning Activity 9.2 with Class 8 students, a teacher reads the 'Safety first' box. Which is the most appropriate safety precaution to emphasise based on Chapter 9?

• A. Wear gloves while stirring water with a glass rod.
• B. Be careful while using the heating device.
• C. Never measure the temperature of water with a thermometer.
• D. Use a 500 mL measuring cylinder for accuracy.

Q13. Is the mixture of gases dissolved in water uniform or non-uniform? The answer is

• A. non-uniform, because gases settle at the bottom
• B. uniform, because the gases dissolve evenly in the water
• C. non-uniform, because oxygen is heavier than water
• D. uniform only above 100 °C

Q14. A bottle has a total capacity of 2 litres. A student first pours 500 mL of water into it. Based on Question 6 of 'Keep the curiosity alive', how much more water can the bottle hold?

• A. 1000 mL
• B. 1200 mL
• C. 1500 mL
• D. 2000 mL

Q15. A teacher uses the chapter's opening prompt with Class 8 students: 'Predict whether the mixture in Fig. 9.1 (sugar, salt, and water) is uniform or not.' Which of these is the best teaching response when a student says 'I can't see anything settling, so I think it is uniform'?

• A. Reject the answer; only experts can decide if a mixture is uniform.
• B. Accept the prediction and confirm that even sip-by-sip the taste is the same, which supports a uniform mixture.
• C. Tell the student the textbook only treats sand-water as a mixture.
• D. Tell the student that uniformity depends only on colour, not taste.

Q16. Which of the following best matches the Snapshot statement in Chapter 9 about solution formation?

• A. A solution is formed only when two solids combine.
• B. A solution is formed only when two gases combine in air.
• C. A solution is formed only at room temperature.
• D. A solution is formed when two or more substances mix to form a uniform mixture.

Q17. Two students compare two glucose solutions: Solution X has 5 g of glucose in 100 mL of water; Solution Y has 10 g of glucose in 200 mL of water. Which conclusion is correct?

• A. Both have the same concentration.
• B. Y is more concentrated than X.
• C. X is more concentrated than Y.
• D. Y is saturated but X is not.

Q18. Chapter 9 carefully writes 'no more solute can be dissolved at that particular temperature' when defining a saturated solution. The phrase 'at that particular temperature' is important because

• A. solubility of solids does not change with stirring
• B. solubility of solids generally increases with temperature, so a saturated solution is saturated only for that temperature
• C. saturation is defined by pressure, not temperature
• D. solubility is the same in every solvent

Q19. Some packets of oil are labelled with a volume of 1 L but a weight of only about 910 g (Fig. 9.11). Based on Chapter 9, this tells us about the density of the oil that it is

• A. greater than that of water
• B. equal to that of water
• C. less than that of water
• D. exactly zero, because oil floats

Q20. Which of the following best explains, in classroom-friendly terms, why ice floating on lakes is important for aquatic life as described in Chapter 9?

• A. Ice insulates the water below, but only if it sinks to the bottom.
• B. Ice floats because it is less dense than liquid water, forming a layer on top and keeping the water below warm enough for fish.
• C. Ice has the same density as water, so it neither sinks nor floats.
• D. Ice raises the temperature of water below to boiling, keeping fish active.

Q21. A Class 8 student writes in her notebook: 'A concentrated solution is the same as a saturated solution.' Which is the most accurate teacher response based on Chapter 9?

• A. Yes, the two terms mean the same thing.
• B. No — concentrated means a lot of solute compared to another solution, while saturated means no more can dissolve at that temperature.
• C. No — concentrated solutions cannot exist at room temperature.
• D. Yes, but only when the solvent is water.

Q22. Two liquids, A and B, are mixed: 80 mL of A and 20 mL of B form a clear single-phase solution. According to Chapter 9's convention for solutions of two liquids, which is the solvent?

• A. A
• B. B
• C. Both A and B are solvents in equal measure.
• D. Neither — the chapter says no solvent can be identified.

Q23. Consider Chapter 9's solute–solvent rules and decide which statement is the most accurate generalisation

• A. The smaller-amount substance is always the solute, with no exceptions.
• B. The larger-amount substance is always the solute for liquids.
• C. In solid-in-liquid solutions, the solid is the solute and the liquid is the solvent; for two liquids the smaller amount is the solute, but exceptions like Gulab jamun chashni exist.
• D. There is no rule — solvents and solutes are decided randomly.

Q24. A glass tube is fixed in a test tube of water (Fig. 9.26 of Chapter 9). When this test tube is placed in a beaker of hot water (~70 °C), the water level in the glass tube rises. The most likely reason is

• A. the mass of the water inside the test tube has increased
• B. the density of the water has decreased on heating, so the same mass occupies more volume
• C. the density of the water has increased on heating, pushing it up
• D. the glass tube has shrunk on heating, raising the water level

Q25. Compare the temperature–solubility relationships for solids and gases in water as described in Chapter 9. Which combination is correct?

• A. Both solids and gases — solubility rises with temperature.
• B. Both solids and gases — solubility decreases with temperature.
• C. Solids — solubility rises with temperature; gases — solubility decreases with temperature.
• D. Solids — solubility decreases with temperature; gases — solubility rises with temperature.

Q26. A block of iron has a mass of 600 g and a density of 7.9 g/cm³. Based on Question 11 of 'Keep the curiosity alive', the volume of the block is approximately

• A. 75.9 cm³
• B. 60.7 cm³
• C. 11.8 cm³
• D. 4740 cm³

Q27. Question 1(ii) of 'Keep the curiosity alive' asks whether 'A mixture of sand and water is a solution' is true. The correct response, based on Chapter 9, is

• A. True, because sand mixed with water forms a uniform mixture.
• B. True, because every mixture is a solution.
• C. False, because sand and water form a non-uniform mixture, not a solution.
• D. False, because sand evaporates faster than water.

Q28. Question 2(iv) of 'Keep the curiosity alive' reads: 'The solution in which glucose has completely dissolved in water, and no more glucose can dissolve at a given temperature, is called a ___________ solution of glucose.' The correct word is

• A. dilute
• B. unsaturated
• C. concentrated
• D. saturated

Q29. Question 2(iii) of 'Keep the curiosity alive' reads: 'Generally, the density ___________ with increase in temperature.' The most appropriate word for the blank is

• A. increases
• B. doubles
• C. remains constant
• D. decreases

Q30. While planning Activity 9.2 with Class 8 students, which one of the following is the best teaching strategy a teacher can adopt, based on Chapter 9's design of the activity?

• A. Skip the 20 °C step and start directly at 70 °C to save time.
• B. Add baking soda only once and only at 20 °C, then conclude.
• C. Take the readings at 20 °C, 50 °C and 70 °C in sequence so that students can see solubility rise with temperature.
• D. Avoid using a thermometer; let students guess the temperature.