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Class 8 Science Chapter 9 The Amazing World of Solutes Solvents and Solutions Extra Questions
Class 8 Science Chapter 9 Extra Questions on The Amazing World of Solutes Solvents and Solutions
The Amazing World of Solutes Solvents and Solutions Class 8 Very Short Question Answer
Question 1.
Define ‘solubility’ and state its unit.
Answer:
Solubility is the maximum solute amount that dissolves in 100 mL solvent at a specific temperature. Its unit is grams per 100 mL (g/100 mL).
Question 2.
Why does cold water hold more oxygen than warm water?
Answer:
Gas solubility decreases with temperature. Cold water’s higher density allows more oxygen to dissolve and supporting aquatic life.
Question 3.
Identify the solute and solvent in Gulab Jamun’s sugar syrup.
Answer:
Solute is sugar and solvent is water. Though sugar is in larger quantity, water dissolves it, making it the solvent
Question 4.
A ship is made of steel (density > water). How does it float? (Competency Based Que.)
Answer:
The ship’s hollow design fills air in it. This air is lighter than water, making its average density less than water’s.
Question 5.
Match the following:
| (i) Saturated solution | (a) Can dissolve more solute |
| (ii) Unsaturated solution | (b) Cannot dissolve more solute |
Answer:
(i) – b,
(ii) – a.
Saturated solutions reach solubility limits and unsaturated solutions can dissolve additional solute.
Question 6.
Justify: “Oil floats on water because its density is less than water.”
Answer:
Objects or liquids that are less dense than water will float on top of it. This is because the denser liquid water will sink below the less dense liquid (air) causing the oil to remain on the surface.
Question 7.
Name the instrument used to measure liquid volume accurately.
Answer:
Measuring cylinder : It is narrow design and graduated markings allow precise volume readings via the meniscus.
Question 8.
When heated, baking soda dissolves in water. What does this show?
Answer:
Solubility of solids increases with temperature. Heating provides energy to break solute-solute bonds and enhancing dissolution.
Question 9.
X = Mass/Volume.
What property does X represent? State its SI unit.
Answer:
X = Density. Its SI unit is kg/m3. It measures how tightly matter is packed.
Question 10.
Select the odd one out: (a) Saltwater (b) Sand+water (c) Sugar syrup. Give reason. (Competency Based Que.)
Answer:
(b) Sand + water. It’s a non-uniform mixture while (a) and (c) are uniform solutions.
Question 11.
Give reason: Ice floats on water despite being solid.
Answer:
The structure of ice changes when it expands its volume, reducing density (0.92 g/cm3) below liquid water’s density (1 g/cm3).
Question 12.
“Air is a gaseous solution.” Which gas is the solvent?
Answer:
Nitrogen is air’s solvent because it’s the most abundant gas (~78%) and dissolving other gases like oxygen.
Question 13.
Calculate density if mass is 300 g and volume is 50 cm3. Will it float in water?
Answer:
Density = 6 g/cm3. It will sink as its density > water’s density (1 g/cm3).
Question 14.
Mention the name and uses of the instruments given below.
Answer:
A is a weighing machine and it is used to measure mass of a substance. B is a measuring cylinder and it is used to measure volume of a substance.
Question 15.
“The density of gases degreases when heated.” Justify with an example.
Answer:
True. Heating air in a balloon increases its volume (expansion) and thus reducing density. This creates lift and making the balloon rise.
The Amazing World of Solutes Solvents and Solutions Class 8 Short Question Answer
Question 1.
“In gulab jamun syrup, sugar is in larger quantities than water, yet water is the solvent.” Justify.
Answer:
The solvent is the substance that dissolves the solute, not necessarily the one in larger quantity. The sugar syrup is made by heating and dissolving large amounts of sugar in less amount of water. Hence, sugar is a solute here and not a solvent.
Question 2.
An iron nail sinks, but a ship made of iron floats. Explain. (Competency Based Que.)
Answer:
A solid nail’s density (7.9 g/cm3) > water, making it sink. Ships are hollow, increasing volume and lowering density below water’s density (1 g/cm3) and thus enabling floating.
Question 3.
“Dissolved oxygen is vital for aquatic life.” Explain why fish survive better in cold water than warm water.
Answer:
Cold water has higher oxygen solubility because the solubility of gases increases on decreasing temperature. Warming water reduces solubility, depriving fish of oxygen, leading to suffocation in extreme cases.
Question 4.
Tabulate two differences between saturated and unsaturated solutions.
Answer:
| Saturated solution | Unsaturated solution |
| 1. Cannot dissolve more solute at a given temperature | Can dissolve additional solute |
| 2. Excess solute settles as residue. | No residue forms. |
Question 5.
What happens to the density of air inside a hot air ballon when heated ? (Competency Based Que.)
Answer:
The density of air inside the hot air balloon decreases. On heating, the volume increases but the mass of air inside the balloon remains the same. Hence, since density = mass/volume, increased volume reduces density, creating lift for the balloon.
Question 6.
Identify the solute and solvent in the following mixtures:
(a) Lemon juice in water
(b) Carbon dioxide in soda.
Answer:
(a) Solute = lemon juice, Solvent = water (liquid dissolves liquid).
(b) Solute = Carbon dioxide, Solvent = water (gas dissolves in liquid under pressure).
Question 7.
Why does a measuring cylinder give more accurate volume readings than a beaker?
Answer:
A measuring cylinder is narrow and tall, so small volume changes (like 1 mL) are easy to see. It has clear markings and a curved liquid surface (meniscus) that you read at eye level for accuracy. A wide beaker can’t measure precisely because small amounts spread out too much.
Question 8.
Reema molds 120 g clay from a cube (60 cm3) to a thin sheet. Does density change? Explain.
Answer:
No. Density depends only on mass and total volume, not shape. Mass (120 g) and volume (60 cm3) remain constant, so density stays 2 g/cm3.
Question 9.
The figure given below represents some objects that can sink or float. The given objects: (a) Wooden block (b) Iron nail (c) Plastic bottle (d) Glass marble.
Which of these will float or sink in water? (Competency Based Que.)
Answer:
| Object | Floats/Sinks |
| (a) Wooden block | Floats |
| (b) Iron nail | Sinks |
| (c) Plastic bottle | Floats |
| (d) Glass marble | Sinks |
Question 10.
“Why does the density gradually increase from the crust (outermost layer) to the inner core (innermost layer)?” (Competency Based Que.)
(i) Support your answer with two observation from the figure.
(ii) Give the states of the outer core and inner core.
Answer:
(i) Density increases from the crust (lightest) to the inner core (densest). This occurs because deeper layers experience extreme pressure and temperature, compressing materials into more compact and heavier forms. The crust is least dense due to its rocky composition, while the inner core is under immense pressure making it the densest layer.
(ii) Outer core is liquid while inner core is solid, indicating extreme pressure compresses materials into denser forms.
The Amazing World of Solutes Solvents and Solutions Class 8 Long Question Answer
Question 1.
“Describe an experiment to demonstrate how temperature affects the solubility of baking soda in water. Include observations and conclusions.”
Answer:
Take 50 mL water in a beaker at 20°C. Add baking soda gradually until saturation (some undissolved powder remains). Now heat to 50°C – the undissolved powder dissolves. Continue heating to 70°C and add more baking soda until saturation again.
Observation
More solute dissolves at higher temperatures.
Conclusion
Solubility of solids increases with temperature as heat provides energy to break molecular bonds.
Question 2.
“Compare and contrast the solubility behavior of solids versus gases in water with respect to temperature changes.”
Answer:
Solids like salt show increased solubility with temperature as heat energy overcomes inter particle forces of attraction. However, gases like oxygen become less soluble because the warm water particles move faster and push the gas molecules outside the water. This explains why aquatic life thrives in cold water (more dissolved oxygen) and why warm soda loses fizz faster. The key difference lies in how temperature affects molecular interactions differently for solids and gases.
Question 3.
“With reference to the meniscus formation in a measuring cylinder, explain how to accurately measure volumes of both colourless and coloured liquids.” (Competency Based Que.)
Answer:
For colourless liquids like water, read the bottom of the concave meniscus at eye level to avoid error. For coloured liquids like ink, read the top of the convex meniscus. The narrow cylinder design magnifies the liquid column, allowing precise measurement of small volume changes (1 mL in 100 mL cylinders) unlike wide beakers where the same volume change would be barely noticeable.
Question 4.
“Compare how pressure affects the density of solids, liquids and gases, with examples from the chapter.”
Answer:
Pressure impacts gases significantly – compressing air in a syringe increases its density by reducing volume. Liquids show minimal density change under pressure because their particles are already close making them nearly incompressible. Solids are least affected – their rigid structure resists compression (like the brick). This variation occurs because intermolecular spaces differ: largest in gases, moderate in liquids, and negligible in solids.
Question 5.
“Describe in detail how you would determine whether a given solution is saturated or unsaturated.”
Answer:
To test if a solution is saturated: First, observe if any undissolved solute particles are settling at the bottom – their presence indicates saturation. Next, try dissolving a small additional amount of the same solute while maintaining constant temperature. If it dissolves, the solution is unsaturated; if not, it’s saturated. For example, if salt stops dissolving in water at 25°C and accumulates at the container’s bottom, the solution has reached its saturation point at that temperature.
Question 6.
(i) What is a solution? Explain with examples from daily life how it differs from a non-uniform mixture.
(ii) What is the relation between a solution and a uniform mixture? Enlist three solutions and three non-uniform mixtures found in homes. (Competency Based Que.)
Answer:
(i) A solution is a uniform mixture where one substance (solute) completely dissolves in another (solvent), forming a clear, stable mixture. Examples include salt water (salt dissolves evenly) and sugar syrup. Unlike solutions, non-uniform mixtures are those where particles don’t dissolve but remain in solvent (like sand in water) and eventually settle.
(ii) Uniform mixtures are called solutions.
| Uniform Mixture | Non-Uniform Mixture |
| Sugar syrup | Sand in water |
| ORS dissolved in water | Sawdust in water |
| Salt in water | Oil in water. |
The Amazing World of Solutes Solvents and Solutions Class 8 Case Based Questions
Question 1.
During a laboratory experiment, Group A was tasked with measuring 50 mL of water using a 100 mL measuring cylinder Fig.(a) – (b). While pouring, they observed the liquid forming a curved surface. A debate arose: some students insisted on reading the top of the curve, while others referred to their textbook which mentioned reading the bottom. Meanwhile, Group B used the same cylinder to measure 30 mL of orange juice, noticing the curve formed differently. (Competency Based Que.)
(i) What is the shape of the water surface in the cylinder, and what is this phenomenon called?
(ii) List two precautions you must follow while measuring 50 mL water using this cylinder, as shown in Fig. (b)
(iii) If the water level appears at 52 mL when viewed from above, but at 50 mL when viewed at eye level, which reading is correct? Why?
Answer:
(i) The water surface is curved upwards. This is called a meniscus.
(ii) Following are the two precautions to be taken
- Place the cylinder on a flat surface to prevent tilting.
- Read the volume at the bottom of the meniscus at eye level to avoid error.
(iii) The 50 mL reading at eye level is correct because viewing from above distorts the meniscus reading.
Question 2.
In a science exhibition, team Neptune created a display about traditional boat-making techniques. Their model showed how ancient civilizations used materials like bamboo and light wood (Fig.(a) to build fishing boats and trade vessels. To demonstrate the science behind this, they conducted experiments comparing different materials: solid teak blocks, hollowed-out logs, and bamboo poles of equal size. Visitors were surprised to see that while all three materials floated, they did so at different levels in the water. (Competency Based Que.)
(i) Why did ancient people prefer bamboo over solid wood for making rafts?
(ii) If team Neptune used three identical-sized blocks- solid wood (0.6 g/cm3), hollow wood (0.3 g/cm3), and bamboo (0.4 g/cm3) – predict their order of floating height from highest to lowest in water. Justify your answer.
(iii) How does the density of a material affect its ability to float in water?
Answer:
(i) Ancient people preferred bamboo over solid wood for making rafts because bamboo is much lighter, hollow and floats on water. Bamboo has air-filled spaces inside, which help it float better than solid wood. This made bamboo easier to carry, build with, and more stable in water, making it ideal for simple rafts and boats.
(ii) The floating height of an object in water depends on its density. The lower the density, the more the object stays above water. In this case, hollow wood (0.3 g/cm3) has the lowest density, so it will float the highest. Next is bamboo (0.4 g/cm3), which will float slightly lower. Solid wood (0.6 g/cm3) has the highest density among the three, so it will float the lowest. So, the order from highest to lowest floating is: hollow wood > bamboo > solid wood.
(iii) Density is how much mass is packed into a given volume of a material. If a material has lower density than water, it will float. If the material has higher density, it will sink. So in boat-making, materials with low density are chosen so that the boat stays on the surface and doesn’t sink.
Question 3.
During a winter field trip to a lake, students observed ice floating on water while the liquid below remained unfrozen. Their teacher explained that water reaches maximum density at 4°C and expands when freezing. This unique property creates an insulating ice layer and protecting aquatic life. (Competency Based Que.)
(i) Why does ice float on water instead of sinking?
(ii) Explain how water’s density changes between 0°C to 4°C and its significance for aquatic ecosystems.
(iii) Why is floating ice important?
Answer:
(i) Ice floats on water because it is less dense than liquid water. When water freezes, it expands and its molecules move farther apart. This means that ice takes up more space but has the same mass, making it lighter per unit volume than water. That is why ice stays on the surface instead of sinking.
(ii) Between 0°C and 4°C, water behaves in a special way. As water is heated from 0°C to 4°C, its density increases, reaching the maximum at 4°C. After that, the density decreases as the temperature rises further.
(iii) Floating ice is important because it forms a protective layer on top of lakes and ponds. This layer keeps the water underneath from freezing completely and acts like a blanket and trapping heat below. As a result, it helps to maintain a stable environment for aquatic life during cold winters.
Skill Based Questions
Question 1.
Complete the crossword puzzle with the help of the clues given below: (Thinking skin)
Across
4. A uniform mixture where solute is evenly spread in solvent.
5. The mass of substance per unit volume.
6. The substance that gets dissolved in a solvent.
Down
1. A liquid that is called the universal solvent.
2. The ability of a substance to dissolve in a solvent.
3. The component that dissolves the solute.
6. A solution in which no more solute can dissolve.
Question 2.
During his summer vacation, Manik visited Iceland and saw ice floating on water in a lake. He became curious and discussed this with his classmate Riya.
Read the conversation and give the answer that follows. (Conceptual)
Question 3.
Answer the following questions based on the table given below. (Analytical Skill)
| Substance | Mass (g) | Volume (cm3) | Solubility in water (g/100mL at 25°C) | Observation in water |
| Salt | 50 | 30 | 36 | Dissolves completely |
| Sand | 50 | 25 | 0.01 | Settles at bottom |
| Oil | 50 | 55 | Insoluble | Floats on surface |
(i) Calculate the density of salt and wax. Which one will sink in water?
(ii) Why does sand settle at the bottom despite having similar mass to salt?
(iii) If we heat water to 80 °C, what change would you expect in salt’s solubility?
The Amazing World of Solutes Solvents and Solutions Extra Questions for Practice
Very Short Answer Type Questions
Question 1.
Name the component in a solution that is responsible for dissolving the solute.
Question 2.
State the visible effect when sugar is stirred into a glass of water.
Question 3.
Identify the type of solution that has the ability to dissolve more solute at a given temperature.
Question 4.
Mention the term used for a solution that has reached its maximum solute holding capacity at a specific temperature.
Short Answer Type Questions
Question 1.
How can you test whether a solution is saturated or not?
Question 2.
Why does stirring or heating help a solute dissolve faster in a solvent?
Question 3.
A glass of salt solution is left uncovered. Explain what happens after some time and why.
Long Answer Type Questions
Question 1.
Give two examples each of solutes and solvents you commonly use at home. For each, mention what kind of solution they form.
Question 2.
Describe how a saturated solution becomes unsaturated on heating. Also explain what happens to the solute particles in this process.