Important Questions for Class 8 Science Chapter 9: The Amazing World of Solutes, Solvents, and Solutions

From the salt dissolved in our oceans to the carbonation in a bottle of soda, solutions are everywhere. Yet, many Class 8 students struggle to connect core concepts like solutes, solvents, and relative density to real-world scenarios and numerical problems. This is where practising important questions for Class 8 Science Chapter 9 by Physics Wallah becomes useful.

Multiple-choice questions, assertion-reason questions, and short answer questions based on the chapter “The Amazing World of Solutes, Solvents, and Solutions” are provided with answers for effective revision. Going through these questions will help students revise key ideas such as solubility, saturation, and relative density. 

What Does Class 8 Science Chapter 9 Cover?

Chapter 9 explains how a solute dissolves in a solvent to form a solution. It covers important concepts like solubility, saturated and unsaturated solutions, dilute and concentrated solutions. The chapter also explains density and relative density and how they help us understand why some objects float while others sink.

Multiple Choice Questions for Class 8 Science Chapter 9 By PW

These multiple-choice questions cover important concepts from the chapter, including solubility, solutions, and density. Practising these questions helps students strengthen their understanding and prepare effectively for exams.

Q1. When a solution cannot dissolve more solute at a particular temperature, it is said to be: 

(A) Unsaturated 

(B) Dilute 

(C) Saturated 

(D) Supersaturated 

Answer: (C) Saturated

Q2. When sawdust is mixed with water, it floats, but sand settles down. Which of the following best explains this observation? 

(A) Sawdust is lighter than water, while sand is heavier than water. 

(B) Both sawdust and sand dissolve completely in water. 

(C) Water attracts sand particles more strongly than sawdust particles. 

(D) Sawdust and sand have equal densities but different sizes. 

Answer: (A) Sawdust is lighter than water, while sand is heavier than water.

Q3. Which statement correctly explains why fish find it harder to survive in warm water? 

(A) Warm water contains more dissolved oxygen due to increased molecular movement. 

(B) Cold water contains less oxygen because gases escape easily at low temperature. 

(C) Solubility of oxygen decreases as temperature increases, reducing oxygen available for aquatic life. 

(D) Temperature does not affect the solubility of gases in water. 

Answer: (C) Solubility of oxygen decreases as temperature increases, reducing the oxygen available for aquatic life.

Q4. Match the substance with its solubility property: 

List 1

P. Common salt, 

Q. Chalk powder, 

R. Sugar 

List 2

(i) Highly soluble in water 

(ii) Insoluble in water 

(iii) Soluble in water 

Answer: (A) P-(iii), Q-(ii), R-(i)

Q5. In traditional Indian medicinal preparations, which of the following acts as a solvent? 

(A) Charcoal and limestone 

(B) Oils, ghee and milk 

(C) Copper and zinc powders 

(D) Ash and clay 

Answer: (B) Oils, ghee and milk

Q6. Lemon juice mixed in water forms a: 

(A) Solute 

(B) Solvent 

(C) Solution 

(D) Suspension 

Answer: (C) Solution — lemon juice (solute) dissolves in water (solvent), forming a solution.

Q7. The maximum amount of solute that can be dissolved in 100 g of solvent at a given temperature is called: 

(A) Concentration 

(B) Solubility 

(C) Saturation 

(D) Miscibility 

Answer: (B) Solubility

Q8. Assertion: The solubility of solids in liquids increases with temperature.  

Reason: On heating, the kinetic energy of particles increases, helping solute particles mix more easily with solvent particles. 

(A) Both Assertion and Reason are true, and Reason is the correct explanation of

Assertion.

(B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.

(C) Assertion is true but Reason is false.

(D) Assertion is false but Reason is true.

Answer: (A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

Q9. Relative density is the ratio of: 

(A) Density of substance to density of mercury 

(B) Density of substance to density of water 

(C) Density of substance to density of air 

(D) Density of water to density of substance 

Answer: (B) Density of substance to density of water (at 4°C). Relative density has no units because it is a ratio.

Q10. A block has a mass of 400 g and a volume of 200 cm³. Its density is: 

(A) 2 g/cm³ 

(B) 0.5 g/cm³ 

(C) 4 g/cm³ 

(D) 20 g/cm³ 

Answer: (A) 2 g/cm³ — Density = Mass ÷ Volume = 400 ÷ 200 = 2 g/cm³.

Class 8 Science Chapter 9 Short Answer Type Questions by PW

Review these conceptual and descriptive questions to deepen your understanding of key chemistry processes, including chemical dissolution, thermal effects on solubility, and physical measurement techniques.

Q11. Define solute and solvent with examples. 

A solute is the substance that dissolves, such as salt, while the solvent is the substance that dissolves the solute, such as water. In a salt solution, salt is the solute and water is the solvent.

Q12. What is the difference between dilute and concentrated solutions? 

A dilute solution contains a small amount of solute compared to the solvent, while a concentrated solution contains a large amount of solute. Both terms are relative, depending on the comparison being made.

Q13. Why does an iron ball sink while a wooden block floats? 

An iron ball has a higher density than water, so it sinks. Wood has a lower density than water, which causes it to float.

Class 8 Science Chapter 9 Long Answer Type Questions by PW

These descriptive questions cover foundational laboratory procedures, fluid behaviour, and conceptual chemistry explanations for Class 8 students.

Q14. Explain the water displacement method for measuring the volume of an irregular solid. 

This method is used to measure the volume of irregular objects that do not have a definite shape. A measuring cylinder is filled with water up to a known level, called the initial volume. The object is then gently lowered into the cylinder so it is completely submerged, causing the water level to rise. 

The final volume is then recorded, and the volume of the object is calculated as: 

Volume = Final volume − Initial volume. 

Since 1 mL equals 1 cm³, this value directly gives the volume of the object.

Q15. Explain why ice floats on water and how this helps aquatic life. 

As water cools to 0°C, it freezes to form ice. During this process, water molecules arrange themselves into an expanded crystal structure, which increases the volume of ice. As a result, the density of ice becomes lower than that of liquid water, so ice floats on the surface. 

This floating ice forms an insulating layer that reduces heat loss from the water below. As a result, deeper water remains in a liquid state at a warmer temperature, allowing aquatic organisms to survive during winter.

Q16. Describe the dissolution of baking soda in water and the effect of temperature on solubility. 

In this activity, baking soda is added to water at room temperature until some of it remains undissolved, indicating that the solution has become saturated. When the solution is heated to 50°C, the undissolved baking soda dissolves. More baking soda is then added until saturation occurs again. 

Heating the mixture further, to 70°C, allows even more solute to dissolve. This experiment shows that the solubility of solids like baking soda increases with temperature, and a solution that is saturated at a lower temperature becomes unsaturated as the temperature rises.