When undissolved solute remains at the bottom, the solution is:

Unsaturated at that temperature

Concentration of a solution refers to:

Amount of solute in a fixed quantity of solution/solvent

Only the amount of solvent used

Which of the following is a more concentrated solution?

4 spoons of salt in 50 mL water

2 spoons of salt in 100 mL water

1 spoon of salt in 200 mL water

Density of a substance compared to water (no units)

Mass of a substance compared to air

Adding salt to water to make an egg float works because:

The density of the solution increases

Ice floats on water mainly because:

Ice is less dense than liquid water

Before weighing a substance on a digital balance with a container, you should:

Tare/reset the balance with the container

For water in a measuring cylinder, volume should be read at the:

Bottom of the meniscus at eye level

Measuring cylinders are tall and narrow mainly to:

Improve reading accuracy (smaller meniscus error)

Which statement about solutions is TRUE?

Components are evenly distributed

Solute particles are visible to naked eye

They always scatter light strongly

Hot air rises mainly because it is:

Less dense than surrounding air

Which pair correctly matches with water?

Sand – non-uniform; Sugar – uniform

Sand – uniform; Sugar – non-uniform

Chalk – uniform; Salt – non-uniform

Sawdust – uniform; Sugar – non-uniform

Continuing to add solute to a saturated solution at the same temperature will:

Decrease solvent volume to zero

A concentrated solution compared to a dilute solution has:

More solute per fixed amount of solvent/solution

NCERT Solutions Class 8 Science - Curiosity Chapter 9 – The Amazing World of Solutes, Solvents, and Solutions

Name: The Amazing World of Solutes, Solvents, and Solutions – Class 8 Science - Curiosity
Uploaded: 2026-05-31
Description: This chapter explains mixtures, solutions, solubility, and density. It shows how substances dissolve to form uniform or non-uniform mixtures, how temperature affects solubility and density, and why some objects float or sink in water—linking science to real-life examples like ORS, Gulab Jamun syrup, and floating ice.

Class 8 Science - Curiosity

Last Updated: 31 May 2026

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Chapter Introduction

This chapter explains mixtures, solutions, solubility, and density. It shows how substances dissolve to form uniform or non-uniform mixtures, how temperature affects solubility and density, and why some objects float or sink in water—linking science to real-life examples like ORS, Gulab Jamun syrup, and floating ice.

हिंदी में (Hindi)

यह अध्याय मिश्रण, विलयन, विलेयता और घनत्व के बारे में बताता है। इसमें समझाया गया है कि पदार्थ कैसे समान या असमान मिश्रण बनाते हैं, तापमान विलेयता और घनत्व को कैसे प्रभावित करता है, और कुछ वस्तुएँ पानी में तैरती या डूबती क्यों हैं—जैसे ओआरएस, गुलाब जामुन की चाशनी और तैरती बर्फ के उदाहरणों से।

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Important Points

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Practice MCQ Questions (66 questions)

Q1. In a homemade ORS (salt + sugar + water), what type of mixture is formed?

Q2. In a salt–water solution, salt is the _ and water is the _.

Q3. Which of the following will form a non-uniform mixture with water?

Q4. Air is best described as a:

Q5. In air, the major component that acts as the solvent is:

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Tough Words (Glossary)

Oral Rehydration Solution (ORS)

Meaning: A mixture used to prevent or treat dehydration

अर्थ: निर्जलीकरण को रोकने या उपचार के लिए बनाया गया मिश्रण

"Doctors give ORS to children with diarrhoea to prevent dehydration."

Dehydration

Meaning: Loss of too much water from the body

अर्थ: शरीर से अधिक पानी का निकल जाना

"Dehydration can cause dizziness and weakness."

Hydrated

Meaning: Having enough water in the body

अर्थ: शरीर में पर्याप्त पानी होना

"Stay hydrated by drinking clean water."

Uniform mixture

Meaning: A mixture that looks the same throughout

अर्थ: ऐसा मिश्रण जो हर जगह समान दिखता है

"Salt water is a uniform mixture."

Non-uniform mixture

Meaning: A mixture where components can be seen separately

अर्थ: ऐसा मिश्रण जिसमें घटक अलग‑अलग दिखाई देते हैं

"Sand in water is a non-uniform mixture."

Solute

Meaning: The substance that dissolves in a liquid

अर्थ: वह पदार्थ जो द्रव में घुलता है

"Sugar is the solute in sugar water."

Solvent

Meaning: The liquid that dissolves another substance

अर्थ: वह द्रव जो किसी पदार्थ को घोलता है

"Water is the solvent in lemonade."

Solution

Meaning: A uniform mixture of solute and solvent

अर्थ: विलयित और विलायक का समान मिश्रण

"Salt solution conducts electricity slightly."

Dissolve

Meaning: To mix completely into a liquid

अर्थ: पूरी तरह द्रव में मिल जाना

"Stir the syrup to help the sugar dissolve."

Chalk powder

Meaning: Fine particles of chalk

अर्थ: चॉक का बारीक चूर्ण

"Chalk powder does not form a uniform solution in water."

Sawdust

Meaning: Tiny pieces of wood

अर्थ: लकड़ी का बुरादा

"Sawdust floats on water."

Concentration

Meaning: Amount of solute in a given amount of solution

अर्थ: विलयन में घुले पदार्थ की मात्रा

"The concentration of salt is higher in seawater."

Dilute

Meaning: Having a small amount of solute

अर्थ: जिसमें घुले पदार्थ की मात्रा कम हो

"This is a dilute sugar solution."

Concentrated

Meaning: Having a large amount of solute

अर्थ: जिसमें घुले पदार्थ की मात्रा अधिक हो

"The syrup is very concentrated."

Saturated solution

Meaning: A solution that cannot dissolve more solute at a given temperature

अर्थ: ऐसा विलयन जिसमें दिए ताप पर अधिक विलेय नहीं घुल सकता

"At room temperature the solution became saturated with salt."

Unsaturated solution

Meaning: A solution that can still dissolve more solute

अर्थ: ऐसा विलयन जिसमें और विलेय घुल सकता है

"Add more sugar to this unsaturated solution."

Solubility

Meaning: Maximum amount of solute that dissolves in a solvent at a given temperature

अर्थ: दिए ताप पर किसी विलायक में घुल सकने वाले विलेय की अधिकतम मात्रा

"The solubility of salt increases slightly with temperature."

Temperature

Meaning: How hot or cold something is

अर्थ: तापमान (गर्मी/ठंडक का माप)

"Temperature affects the solubility of many solids."

Baking soda

Meaning: A common chemical called sodium hydrogen carbonate

अर्थ: सोडियम हाइड्रोजन कार्बोनेट नामक सामान्य रसायन

"Baking soda dissolves more in warm water."

Demonstration

Meaning: A practical showing of how something works

अर्थ: व्यावहारिक प्रदर्शन

"The teacher gave a demonstration of making lime water."

Vigorously

Meaning: With a lot of energy and force

अर्थ: जोरदार तरीके से

"Calcium oxide reacts vigorously with water."

Calcium hydroxide (lime water)

Meaning: A solution formed when calcium oxide reacts with water

अर्थ: कैल्शियम ऑक्साइड के पानी से अभिक्रिया करने पर बना घोल (चूना‑जल)

"Lime water turns milky with carbon dioxide."

Gaseous solution

Meaning: A solution made of gases

अर्थ: गैसों से बना विलयन

"Air is a gaseous solution with nitrogen as solvent."

Aquatic

Meaning: Living in water

अर्थ: जल में रहने वाला

"Dissolved oxygen supports aquatic life."

Minute (quantity)

Meaning: Very small

अर्थ: अत्यंत थोड़ी

"Only a minute quantity of oxygen dissolves in water."

Float

Meaning: To stay on the surface of a liquid

अर्थ: तरल की सतह पर टिके रहना/तैरना

"Oil drops float on water."

Sink

Meaning: To go down to the bottom of a liquid

अर्थ: तरल के तल में चला जाना

"The stone will sink in water."

Husk

Meaning: The outer covering of grains

अर्थ: धान/अनाज का छिलका

"Husk floats while washing rice."

Density

Meaning: Mass per unit volume of a substance

अर्थ: किसी पदार्थ का इकाई आयतन पर द्रव्यमान (सघनता)

"Ice has lower density than water."

Relative density

Meaning: Density of a substance compared to water

अर्थ: पानी की सापेक्ष सघनता

"Aluminium has a relative density of about 2.7."

Unit

Meaning: A standard quantity used for measurement

अर्थ: मापन की मानक मात्रा (इकाई)

"The SI unit of density is kg/m³."

Kilogram per cubic metre (kg/m³)

Meaning: SI unit of density

अर्थ: सघनता की एसआई इकाई

"Air has a density of about 1.2 kg/m³ at room temperature."

Gram per millilitre (g/mL)

Meaning: Common unit of density for liquids

अर्थ: तरल पदार्थों की सघनता की सामान्य इकाई

"The density of water is about 1 g/mL."

Meniscus

Meaning: The curved surface of a liquid in a container

अर्थ: बर्तन में तरल की वक्र सतह (मेनीस्कस)

"Read the volume at the bottom of the meniscus."

Measuring cylinder

Meaning: A tall cylinder used to measure liquid volume

अर्थ: तरल का आयतन नापने का बेलनाकार यंत्र

"Use a measuring cylinder to take 50 mL of water."

Tare

Meaning: To reset a balance to zero with a container on it

अर्थ: तौल यंत्र को पात्र सहित शून्य पर सेट करना

"Press tare before weighing the powder."

Cuboid

Meaning: A 3D shape with rectangular faces

अर्थ: आयताभ (आयताकार घनाभ) आकृति

"We measured the volume of a cuboid box."

Irregular shape

Meaning: A shape that is not uniform or standard

अर्थ: अनियमित आकार

"Use water displacement to find the volume of an irregular shape."

Displacement method

Meaning: Finding volume by how much water level rises

अर्थ: जल स्तर बढ़ने से आयतन मापने की विधि (विस्थापन विधि)

"The stone’s volume was found by the displacement method."

Apparatus

Meaning: The tools or equipment used in an experiment

अर्थ: प्रयोग में इस्तेमाल होने वाले उपकरण

"Collect the apparatus before starting the activity."

Graduations

Meaning: The marked divisions on a measuring instrument

अर्थ: माप यंत्र पर अंकित विभाजन

"Check the graduations to read the exact volume."

Compressed

Meaning: Pressed into a smaller space

अर्थ: दबा कर छोटे आयतन में करना (संपीड़ित)

"Air can be compressed easily."

Approximate

Meaning: Not exact but close

अर्थ: लगभग/आनुमानित

"10 mL of water has an approximate mass of 10 g."

Thermal expansion

Meaning: Increase in volume when heated

अर्थ: ताप से आयतन का बढ़ना (ऊष्मीय प्रसार)

"Thermal expansion lowers the density of hot air."

Pressure

Meaning: Force applied per unit area

अर्थ: इकाई क्षेत्रफल पर लगाया गया बल (दाब)

"High pressure increases the density of gases."

Hydro-alcoholic

Meaning: Made with water and alcohol together

अर्थ: जल व अल्कोहल मिश्रित

"Some herbal extracts use a hydro-alcoholic solvent."

Formulation

Meaning: A prepared mixture for a specific purpose (like medicine)

अर्थ: विशेष उद्देश्य हेतु तैयार मिश्रण (निर्मित दवा)

"This cough syrup is a new formulation."

Therapeutic

Meaning: Related to healing or treatment

अर्थ: उपचार से संबंधित (चिकित्सीय)

"The oil has therapeutic value."

Extract

Meaning: To remove a substance from a mixture

अर्थ: किसी मिश्रण से पदार्थ निकालना (अर्क/निष्कर्ष निकालना)

"Scientists extract useful compounds from plants."

Isolate

Meaning: To separate something from other things

अर्थ: अलग करना/विलग करना

"They isolate the active ingredient from leaves."

Conduct

Meaning: To carry out or perform

अर्थ: करना/संचालित करना

"We will conduct Activity 9.1 in class."

Determine

Meaning: To find out or calculate

अर्थ: निर्धारित करना/पता लगाना

"Determine the density from mass and volume."

Pop sound

Meaning: A small bursting sound heard in gas tests

अर्थ: हल्की फूट जैसी आवाज़

"Hydrogen burns with a pop sound."

Room temperature

Meaning: Normal indoor temperature

अर्थ: सामान्य कमरे का तापमान

"The density of water is 1 g/mL at room temperature."

Solubility (of gases)

Meaning: How much gas dissolves in a liquid

अर्थ: गैसों की विलेयता

"The solubility of oxygen is higher in cold water."

NCERT Solutions Class 8 Science - Curiosity Chapter 9 – The Amazing World of Solutes, Solvents, and Solutions

Chapter Introduction

Watch Video Lecture

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Important Points

Practice MCQ Questions (66 questions)

Q1. In a homemade ORS (salt + sugar + water), what type of mixture is formed?

Q2. In a salt–water solution, salt is the ___ and water is the ___.

Q3. Which of the following will form a non-uniform mixture with water?

Q4. Air is best described as a:

Q5. In air, the major component that acts as the solvent is:

Q6. A solution that can still dissolve more solute at a given temperature is called:

Q7. When undissolved solute remains at the bottom, the solution is:

Q8. Concentration of a solution refers to:

Q9. Which of the following is a more concentrated solution?

Q10. Solubility of most solid solutes in water generally:

Q11. A saturated solution at 30 °C is heated to 50 °C. It will likely become:

Q12. The solubility of gases in water generally ___ with increase in temperature.

Q13. Dissolved oxygen in water is important because it:

Q14. Density is defined as:

Q15. SI unit of density is:

Q16. Which pair of units is commonly used for liquid densities?

Q17. Relative density is:

Q18. If aluminium has density 2.7 g/cm³, its relative density (with respect to water ~1 g/cm³) is:

Q19. An object floats in water primarily when its density is:

Q20. Adding salt to water to make an egg float works because:

Q21. Ice floats on water mainly because:

Q22. Mass is measured in ___, while weight is measured in ___.

Q23. Before weighing a substance on a digital balance with a container, you should:

Q24. Which instrument is best suited to measure liquid volume accurately in school labs?

Q25. For water in a measuring cylinder, volume should be read at the:

Q26. The smallest division of a 100 mL measuring cylinder typically represents:

Q27. Volume of a cuboid is calculated using:

Q28. Volume of an irregular stone can be found by:

Q29. If water level rises from 50 mL to 65 mL after immersing a key, the key’s volume is:

Q30. Given mass = 16.400 g and volume = 5 cm³, density equals:

Q31. Measuring cylinders are tall and narrow mainly to:

Q32. To measure 70 mL most accurately in one step, choose a:

Q33. When two liquids form a solution, the solvent is generally the component present in:

Q34. Which statement about solutions is TRUE?

Q35. ORS tastes the same in every sip because:

Q36. Generally, on heating a substance, its density:

Q37. Hot air rises mainly because it is:

Q38. Increasing pressure noticeably increases density mostly for:

Q39. Which pair correctly matches with water?

Q40. Sawdust floats in water mainly because its:

Q41. Oil floating over water indicates oil has:

Q42. While reading liquid level, eyes should be:

Q43. A 1 L oil pack shows ‘910 g’. This tells that oil’s density is:

Q44. Which gas is the major solute in air?

Q45. Which statement about gaseous solutions is CORRECT?

Q46. Continuing to add solute to a saturated solution at the same temperature will:

Q47. A concentrated solution compared to a dilute solution has:

Q48. If density = mass/volume, then mass equals:

Q49. 1 mL is exactly equal to:

Q50. The most appropriate unit for density of a metal block in school lab is:

Q51. Water has maximum density at:

Q52. When water freezes to ice, volume ___ and density ___.

Q53. While dissolving solute to test solubility vs temperature, one should:

Q54. To compare solubility at different temperatures, the variable to change is:

Q55. Which is TRUE for solutions?

Q56. Which mixture will show visible settling over time?

Q57. Which change makes baking soda dissolve more at once in water?

Q58. The meniscus of water in a glass cylinder is:

Q59. Overhead tanks are placed high mainly to:

Q60. If two solutions have the same solute and solvent, the one with more solute per unit volume is:

Q61. When a saturated solution at 70 °C is cooled to 25 °C, some solute may:

Q62. Which statement about density is INCORRECT?

Q63. For gases, increasing pressure while keeping temperature constant generally:

Q64. Gulab jamun chashni is sugar in little water. Here solvent is:

Q65. If 100 mL water has a mass of ~100 g at room temperature, its density is about:

Q66. Which BEST explains why sawdust floats but sand sinks in water?