A solution is a uniform mixture formed when a solute dissolves in a solvent. Important Questions Class 8 Science Chapter 9 cover solute, solvent, solution, saturated and unsaturated solutions, solubility, temperature effect, density, floating, sinking, and displacement method.
A glass of ORS tastes the same in every sip. Salt disappears in water, but sand settles at the bottom. Oil floats on water, while a stone sinks.
Class 8 Science Chapter 9 explains these everyday observations through solutions and density. The chapter becomes easier when students understand two ideas clearly: how substances dissolve and how density decides whether objects float or sink.
Key Takeaways
| Topic |
What to Revise |
| Solution |
Uniform mixture of solute and solvent |
| Solute |
Substance that dissolves |
| Solvent |
Substance that dissolves the solute |
| Saturated Solution |
No more solute can dissolve at that temperature |
| Unsaturated Solution |
More solute can still dissolve |
| Solubility |
Maximum solute dissolved in 100 mL solvent at a given temperature |
| Temperature Effect |
Solid solubility usually increases on heating |
| Gas Solubility |
Gas solubility usually decreases on heating |
| Density |
Density = Mass / Volume |
| Relative Density |
Density of substance / Density of water |
| Displacement Method |
Volume of irregular solid = rise in water level |
| Floating and Sinking |
Object floats if its density is less than liquid density |
Class 8 Science Chapter List
Important Topics in The Amazing World of Solutes, Solvents, and Solutions
Class 8 science chapter 9 important questions come from two main clusters. The first cluster covers solutions, solubility, and concentration. The second cluster covers density, floating, sinking, and volume measurement.
- Uniform and non-uniform mixtures
- Solute, solvent, and solution
- Saturated and unsaturated solutions
- Concentrated and dilute solutions
- Solubility of solids in water
- Effect of temperature on solubility
- Solubility of gases in water
- Density and density formula
- Relative density
- Floating and sinking
- Measuring mass using a weighing balance
- Measuring volume using a measuring cylinder
- Meniscus reading
- Displacement method for irregular solids
- Effect of temperature and pressure on density
Very Short Answer Questions from Class 8 Science Chapter 9
One-mark questions test exact definitions, terms, units, and basic facts.
Keep answers short and use correct scientific terms.
Class 8 Science Chapter 9 Question Answer
Q1. What is a solution?
Ans. A solution is a uniform mixture in which two or more substances mix evenly.
Example: Salt dissolved in water.
Q2. What is a solute?
Ans. The solute is the substance that dissolves in a solution.
Example: Salt is the solute in saltwater.
Q3. What is a solvent?
Ans. The solvent is the substance that dissolves the solute.
Example: Water is the solvent in saltwater.
Q4. What is solubility?
Ans. Solubility is the maximum amount of solute that can dissolve in 100 mL of solvent at a particular temperature.
Q5. Define density.
Ans. Density is the mass present in unit volume of a substance.
Density = Mass / Volume
Its SI unit is kg/m³.
Q6. What is a saturated solution?
Ans. A saturated solution is a solution in which no more solute can dissolve at a given temperature.
Q7. What is an unsaturated solution?
Ans. An unsaturated solution is a solution in which more solute can still dissolve at a given temperature.
Q8. Which instrument measures the mass of a solid object in the laboratory?
Ans. A digital weighing balance measures the mass of a solid object.
Q9. What is a meniscus?
Ans. The curved surface formed by a liquid inside a measuring cylinder is called the meniscus.
For water and colourless liquids, volume is read from the bottom of the meniscus.
Q10. What is relative density?
Ans. Relative density is the ratio of the density of a substance to the density of water at the same temperature.
Relative density has no unit.
Short Answer Questions on Solute, Solvent, and Solution
These the amazing world of solutes solvents and solutions important questions test whether students understand uniform mixtures.
Use examples like ORS, saltwater, sugar syrup, and air.
Solute, Solvent and Solution Questions
Q1. Why does every sip of ORS taste the same throughout the glass?
Ans. ORS is a solution.
When sugar and salt dissolve in water, they spread evenly throughout the liquid. So, every sip has the same concentration and tastes the same.
Q2. How is a uniform mixture different from a non-uniform mixture? Give one example of each.
Ans. In a uniform mixture, the components are evenly distributed.
Example: Salt dissolved in water.
In a non-uniform mixture, the components are not evenly distributed and can be seen separately.
Example: Sand mixed with water.
Q3. In gulab jamun chashni, sugar is present in a larger quantity than water. Is water still the solvent? Why?
Ans. Yes, water is still the solvent.
Sugar dissolves in water, so sugar is the solute and water is the solvent. Here, water acts as the dissolving medium.
Q4. Can a mixture of gases be considered a solution? Give a reason.
Ans. Yes, a mixture of gases can be a solution.
Air is a uniform mixture of gases. Its components are evenly distributed, so air is considered a solution.
Q5. What does concentration of a solution mean? How is it different from solubility?
Ans. Concentration means the amount of solute present in a fixed quantity of solution.
Solubility means the maximum amount of solute that can dissolve in a fixed quantity of solvent at a particular temperature.
Concentration tells how much solute is present. Solubility tells the maximum limit.
Saturated and Unsaturated Solutions Questions
Saturated and unsaturated solution questions are common in class tests.
The key idea is whether more solute can still dissolve at the same temperature.
The Amazing World of Solutes Solvents and Solutions Class 8 Questions and Answers
Q1. What happens when you keep adding salt to water past a certain point?
Ans. Initially, salt dissolves in water.
After a point, no more salt dissolves and extra salt settles at the bottom.
This shows that the solution has become saturated at that temperature.
Q2. Which is more concentrated: 2 spoons of salt in 100 mL water or 4 spoons of salt in 50 mL water?
Ans. The second solution is more concentrated.
It has 4 spoons of salt in only 50 mL water. So, the amount of solute compared to solvent is higher.
Q3. State whether each statement is true or false. Correct the false ones.
(i) An unsaturated solution has more solute dissolved than a saturated solution.
(ii) A mixture of sand and water is a solution.
(iii) The presence of different gases in the atmosphere is a uniform mixture.
Ans.
(i) False. A saturated solution has the maximum amount of solute dissolved at that temperature.
(ii) False. Sand and water form a non-uniform mixture, not a solution.
(iii) True. Air is a uniform mixture of gases.
Q4. Can a concentrated solution be unsaturated?
Ans. Yes, a concentrated solution can still be unsaturated.
A concentrated solution has a large amount of solute. But if it can still dissolve more solute at that temperature, it is unsaturated.
Questions on Effect of Temperature on Solubility
Temperature changes how much solute can dissolve in a solvent.
For most solids, solubility increases on heating. For gases, solubility usually decreases on heating.
Class 8 Science Chapter 9 Important Questions
Q1. In an activity, baking soda stopped dissolving in water at 20°C. When the water was heated to 50°C, the undissolved baking soda dissolved again. What does this show?
Ans. This shows that the solubility of baking soda increases with temperature.
The solution was saturated at 20°C. After heating, it became unsaturated because more solute could dissolve.
Q2. How does increasing temperature affect the solubility of gases in water?
Ans. Increasing temperature decreases the solubility of gases in water.
Cold water can hold more dissolved oxygen than warm water. This is why aquatic organisms often survive better in cooler water.
Q3. A saturated salt solution is prepared at 30°C. If the temperature is raised to 60°C, will it remain saturated?
Ans. No, it will usually become unsaturated.
When temperature rises, the solubility of most solids increases. So, the solution can dissolve more salt at 60°C.
Q4. Why does oxygen dissolve less in warm water?
Ans. In warm water, gas molecules move faster and escape more easily from the liquid.
So, less oxygen remains dissolved in warm water.
MCQs from The Amazing World of Solutes, Solvents, and Solutions
These the amazing world of solutes solvents and solutions mcq questions test key concepts from both solutions and density.
Read each option carefully before answering.
Class 8 Science Chapter 9 MCQs
Q1. You pour oil into a glass containing water. The oil floats on top. What does this show?
(a) Oil is denser than water
(b) Water is denser than oil
(c) Oil and water have the same density
(d) Oil dissolves in water
Ans. (b) Water is denser than oil.
Oil floats because its density is lower than water.
Q2. Which of the following is a non-uniform mixture?
(a) Salt in water
(b) Sugar in water
(c) Sand in water
(d) Oxygen in water
Ans. (c) Sand in water.
Sand does not dissolve evenly in water and settles at the bottom.
Q3. A solution that can dissolve no more solute at a given temperature is called:
(a) Dilute solution
(b) Unsaturated solution
(c) Saturated solution
(d) Concentrated solution
Ans. (c) Saturated solution.
A saturated solution cannot dissolve more solute at that temperature.
Q4. The SI unit of density is:
(a) g/cm³
(b) g/mL
(c) kg/m³
(d) mg/L
Ans. (c) kg/m³.
The SI unit of density is kilogram per cubic metre.
Q5. The solubility of gases in liquids generally:
(a) Increases with temperature
(b) Decreases with temperature
(c) Remains unchanged with temperature
(d) First increases, then decreases
Ans. (b) Decreases with temperature.
Gases are generally less soluble in warm liquids.
Q6. Object A has mass 200 g and volume 40 cm³. Object B has mass 240 g and volume 60 cm³. Which object is denser?
(a) Object A
(b) Object B
(c) Both are equally dense
(d) Cannot determine
Ans. (a) Object A.
Density of A = 200/40 = 5 g/cm³
Density of B = 240/60 = 4 g/cm³
Object A is denser.
Important Questions on Density, Floating and Sinking
Density questions class 8 science are among the most important questions in this chapter.
An object floats if its density is less than the density of the liquid. It sinks if its density is greater.
Density Questions Class 8 Science
Q1. A wooden stick and an iron rod are of the same size. The iron rod feels much heavier. What property causes this difference?
Ans. The property is density.
Iron has more mass packed into the same volume than wood. So, iron has higher density and feels heavier.
Q2. Why does sawdust float but sand sink in water?
Ans. Sawdust floats because its density is lower than water.
Sand sinks because its density is higher than water.
Q3. Why does ice float on water?
Ans. Ice floats because its density is lower than liquid water.
When water freezes, it expands. The same mass occupies more volume, so the density of ice becomes less than water.
Q4. Why does an unpeeled orange float but a peeled orange sink?
Ans. An unpeeled orange has air pockets in its peel.
These air pockets reduce its overall density, so it floats. When the peel is removed, the orange becomes denser than water and sinks.
Q5. Why do hot air balloons rise?
Ans. Hot air balloons rise because hot air is less dense than cool air.
When air is heated, its volume increases while mass remains nearly the same. So, its density decreases and the balloon rises.
Numerical Questions on Density and Volume
Numerical questions from this chapter usually use the formula:
Density = Mass / Volume
Always write units correctly.
Class 8 Science Chapter 9 Extra Questions
Q1. A stone sculpture has mass 225 g and volume 90 cm³. Calculate its density. Will it float or sink in water?
Ans.
Density = Mass / Volume
= 225 / 90
= 2.5 g/cm³
The density of water is 1 g/cm³.
Since 2.5 g/cm³ is greater than 1 g/cm³, the stone will sink.
Q2. An object has mass 400 g and volume 40 cm³. What is its density?
Ans.
Density = Mass / Volume
= 400 / 40
= 10 g/cm³
Q3. Object A has mass 200 g and volume 40 cm³. Object B has mass 240 g and volume 60 cm³. Which is denser?
Ans.
Density of A = 200 / 40
= 5 g/cm³
Density of B = 240 / 60
= 4 g/cm³
Object A is denser.
Q4. A block of iron has mass 600 g and density 7.9 g/cm³. Find its volume.
Ans.
Volume = Mass / Density
= 600 / 7.9
= 75.9 cm³ approximately
Q5. A stone is lowered into a measuring cylinder containing 50 mL water. The water level rises to 55 mL. The mass of the stone is 16.400 g. Calculate its density.
Ans.
Volume of stone = Final water level - Initial water level
= 55 - 50
= 5 mL
Since 1 mL = 1 cm³,
Volume = 5 cm³
Density = Mass / Volume
= 16.400 / 5
= 3.28 g/cm³
Q6. Reema has modelling clay weighing 120 g. She moulds it into a compact cube and then flattens it into a thin sheet. Does its density change?
Ans. The density of the clay does not change only because its shape changes.
Mass remains the same. The material also remains the same.
For the same substance, changing shape does not change density.
Q7. A bottle has volume 2 litres. You pour 500 mL water into it. How much more water can it hold?
Ans.
2 litres = 2000 mL
Water already poured = 500 mL
Remaining capacity = 2000 - 500
= 1500 mL
Experiment and Activity-Based Questions from Class 8 Science Chapter 9
Activity-based questions test observation, method, and conclusion.
Write steps clearly and include the scientific reason.
The Amazing World of Solutes Solvents and Solutions Class 8 Extra Questions and Answers
Q1. In an activity, a stone of mass 16.400 g is immersed in a measuring cylinder. The water level rises from 50 mL to 55 mL. Write the steps to calculate the stone’s density.
Ans.
Step 1: Find the volume by displacement.
Volume = Final water level - Initial water level
= 55 - 50
= 5 mL
= 5 cm³
Step 2: Apply density formula.
Density = Mass / Volume
= 16.400 / 5
= 3.28 g/cm³
Q2. A test tube is placed in hot water. The water level in the glass tube rises. How does this affect the density of water?
Ans. When water is heated, its volume increases.
Its mass remains the same.
Density = Mass / Volume
Since volume increases while mass stays the same, density decreases.
Q3. Why should the measuring cylinder be read at eye level?
Ans. Reading at eye level gives the correct volume.
If the cylinder is read from above or below, the meniscus appears at the wrong level and gives an incorrect reading.
Q4. Why are measuring cylinders tall and narrow instead of wide and short?
Ans. A tall and narrow cylinder shows a clearer rise in liquid level for a small volume change.
This makes volume reading more accurate.
Q5. How is the volume of an irregular solid measured?
Ans. The volume of an irregular solid is measured by water displacement.
First note the initial water level. Then lower the solid into water. The rise in water level gives the volume of the solid.
Case-Based Questions from The Amazing World of Solutes, Solvents, and Solutions
Case-based questions connect chapter concepts with real-life examples.
Read the passage and identify the concept before answering.
Case Study 1: Dead Sea
The Dead Sea has a very high concentration of dissolved salts. This makes its water much denser than ordinary seawater or river water.
Q1. Why do humans float easily in the Dead Sea without swimming?
Ans. Dead Sea water has very high salt concentration.
This increases the density of water. Since the human body is less dense than Dead Sea water, people float easily.
Q2. Why is there very little aquatic life in the Dead Sea?
Ans. The salt concentration is extremely high.
Most aquatic organisms cannot survive in such salty water because their body cells cannot tolerate the high salt level.
Case Study 2: Oil and Density
Some packets of cooking oil are labelled as 1 litre, but the mass is about 910 g.
Q1. What does this tell us about the density of oil?
Ans.
Density = Mass / Volume
= 910 g / 1000 mL
= 0.91 g/mL
Since 0.91 g/mL is less than the density of water, oil is less dense than water.
Q2. Why does oil float on water?
Ans. Oil floats because its density is lower than water.
It also does not mix uniformly with water, so it forms a separate upper layer.
Case Study 3: Egg in Salt Water
An egg sinks in tap water. A student adds salt to the water and stirs. After enough salt is added, the egg starts floating.
Q1. Why does the egg begin to float after salt is added?
Ans. Adding salt increases the density of water.
When the salt solution becomes denser than the egg, the egg floats.
Q2. Is this example related to solution or density?
Ans. It is related to both.
Salt dissolves in water to form a solution. The dissolved salt increases the density of the solution.
Extra Questions and Answers for Class 8 Science Chapter 9
These questions test deeper understanding of solutions, density, and real-life applications.
Class 8 Science Chapter 9 Notes-Based Questions
Q1. The density of aluminium is 2.7 g/cm³. What is its relative density with respect to water?
Ans.
Relative density = Density of aluminium / Density of water
= 2.7 / 1
= 2.7
Relative density has no unit.
Q2. What is the effect of pressure on density of gases, liquids, and solids?
Ans. In gases, pressure has a large effect on density.
When pressure increases, gas volume decreases and density increases.
In liquids, pressure has only a small effect because liquids are nearly incompressible.
In solids, pressure has a very small effect because particles are tightly packed.
Q3. Explain why hot air rises above cool air.
Ans. Hot air rises because it is less dense than cool air.
When air is heated, particles move farther apart. Its volume increases, while mass remains almost the same. So, density decreases.
Q4. Why does density increase from Earth’s crust to its inner core?
Ans. Density increases toward Earth’s inner core because pressure increases with depth.
Deeper layers also contain heavier materials. The inner core is under very high pressure, making it the densest layer.
Q5. Why is sand in water not a solution?
Ans. Sand does not dissolve in water.
It remains visible and settles at the bottom. So, sand and water form a non-uniform mixture, not a solution.
Important Formulas from Class 8 Science Chapter 9
| Concept |
Formula / Rule |
| Density |
Density = Mass / Volume |
| Volume |
Volume = Mass / Density |
| Mass |
Mass = Density × Volume |
| Relative Density |
Density of substance / Density of water |
| Displacement Method |
Volume of object = Final water level - Initial water level |
| Floating Rule |
Object floats if its density is less than liquid density |
| Sinking Rule |
Object sinks if its density is greater than liquid density |
| Solid Solubility on Heating |
Usually increases |
| Gas Solubility on Heating |
Usually decreases |