The Amazing World of Solutes, Solvents, and Solutions

(b) solution

(a) sugar

(d) water

(c) solvent

(a) solute

(b) water is still considered the solvent

(c) the components are evenly distributed

(b) Chalk powder

(d) unsaturated

(b) undissolved solute settles at the bottom

(c) concentration

(d) dilute

(a) relative terms

(c) 4 spoons of salt in 50 mL of water

(d) solubility

(c) sodium hydrogen carbonate

(b) increases

(a) unsaturated

(b) decreases

(c) only to a small extent

(b) all aquatic life, including plants and fishes

(d) cold water

(a) anti-epileptic and anti-malarial drugs

(d) Shanti Swarup Bhatnagar Award in chemical science

(b) mass per unit volume

(c) kg/m³

(b) 1 g

(c) 100 g

(d) 2.7 g/cm³

(c) 2.7

(b) a number without any units

(a) less dense than water

(c) shape and size

(d) Gases

(a) they are less dense than water

(b) it is less dense than the cool air around it

(a) decreases

(d) volume increases

(c) 4 °C

(b) it is less dense than water due to expansion

(a) keeps the water underneath warm enough for survival

(d) add salt to the water

(a) matter present in an object

(d) newtons

(a) tare or reset button

(b) cubic metre (m³)

(d) 1 dm³

(b) 1 cm³

(a) measure volume more accurately

(c) 1 mL

(d) bottom

(c) meniscus

(d) 5 cm³

(c) 3.28 g/cm³

(a) increases

solution

sugar

solvent

saturated

concentration

solubility

increases

decreases

Mass

kg/m³

meniscus

bottom

volume

balance (weighing balance)

4

False (chalk powder forms a non-uniform mixture, not a solution)

False (sugar is the solute; water is the solvent)

True

True

False (it generally decreases with increase in temperature)

True

False (they are relative terms)

True

False (density is independent of shape and size)

True

False (for coloured liquids it is taken at the top of the meniscus)

False (pressure affects the density of gases the most)

True

False (on heating, the volume increases and density decreases)

True

A–3, B–4, C–1, D–5, E–2

A–4, B–3, C–2, D–5, E–1

(b)

(d) — A saturated solution cannot dissolve more solute at the same temperature; it requires heating to behave as unsaturated.

(b) — The water level rises (volume increases) and density decreases; R is false because density decreases, not increases, on heating.

(c) — Both are true, but R gives an example of a dissolved gas rather than explaining why gases dissolve in water.

(d)

(a)

(c) — The 100 mL cylinder is more accurate because it has a smaller smallest reading; R is true but shows A is false.

(a)

Hint: Solute = the component that dissolves (e.g., salt); solvent = the component in which the solute dissolves (e.g., water); solution = the uniform mixture formed (e.g., salt solution).

Hint: When sugar and salt are mixed with water they form a uniform mixture in which the components are evenly distributed throughout, so every sip has the same composition.

Hint: The liquid present in the smaller amount is the solute and the one in the larger amount is the solvent; e.g., in vinegar, acetic acid (smaller amount) is the solute and water is the solvent.

Hint: Water is considered the solvent even though it is present in a smaller amount than sugar; this is surprising because the larger amount (sugar) is still the solute.

Hint: An unsaturated solution can dissolve more solute at a given temperature, whereas a saturated solution cannot — the extra solute settles at the bottom.

Hint: Concentration is the amount of solute present in a fixed quantity of solution or solvent. A dilute solution has less solute; a concentrated solution has more solute (the terms are relative).

Hint: Solubility is the maximum amount of solute that dissolves in a fixed quantity of the solvent (or solution) at a particular temperature.

Hint: For most solids, solubility increases with temperature; a saturated solution at a lower temperature behaves as unsaturated when heated, allowing more solute to dissolve.

Hint: It behaves as an unsaturated solution because the solubility of the solid increases with temperature, so more solute can now dissolve.

Hint: The solubility of gases decreases with temperature, so warm water holds less dissolved oxygen, leaving insufficient oxygen for aquatic life.

Hint: Density is the mass present in a unit volume of a substance. Formula: Density = Mass / Volume; SI unit = kg/m³.

Hint: Relative density = density of a substance / density of water at that temperature. It is a ratio of two densities, so the units cancel out and it has no units.

Hint: Since 1 L of water weighs about 1000 g but 1 L of oil weighs only 910 g, oil is less dense than water (relative density ≈ 0.91).

Hint: Mass is the quantity of matter present in an object (measured in g or kg); weight is the force by which the Earth attracts the object and is measured in newtons (N).

Hint: 1 litre = 1 dm³, and 1 mL = 1 cm³; volume of liquids is expressed in litres and millilitres.

Hint: A narrow and tall design makes the liquid column taller for a given volume, so small changes in volume give a larger, more accurate reading.

Hint: For colourless liquids, read the mark at the bottom of the meniscus; for coloured liquids, read the mark at the top of the meniscus. Keep eyes level with the meniscus.

Hint: Note the initial water level in a measuring cylinder (say 50 mL), lower the tied stone into it, and note the final level (say 55 mL). Volume of the stone = final − initial = 5 cm³.

Hint: Density = Mass / Volume = 400 g / 40 cm³ = 10 g/cm³.

Hint: Volume = Mass / Density = 600 g ÷ 7.9 g/cm³ ≈ 75.95 cm³ (about 76 cm³).

Introduction: A solution is a uniform mixture formed when one substance dissolves completely in another.
Key Points:
1. Solid-in-liquid — The dissolved solid is the solute and the liquid is the solvent, like sugar or salt in water.
2. Two liquids — The liquid in smaller amount is the solute and the one in larger amount is the solvent, as in vinegar.
3. Solute + Solvent → Solution — The solute dissolves in the solvent to form a uniform mixture called a solution.
Conclusion: Identifying solute and solvent depends on the physical states and relative amounts of the components.

Introduction: Solutions are classified by how much solute they hold at a given temperature.
Key Points:
1. Unsaturated solution — It can still dissolve more solute at the given temperature without any settling.
2. Saturated solution — No more solute dissolves; the extra solute settles at the bottom at that temperature.
3. Conversion — Heating a saturated solution increases solubility, so it behaves as an unsaturated solution again.
Conclusion: Saturation depends on temperature; heating turns a saturated solution unsaturated.

Introduction: The baking soda activity shows how temperature controls the dissolving capacity of a solvent.
Key Points:
1. Set-up — Baking soda (sodium hydrogen carbonate) is added to 50 mL water at 20 °C until some remains undissolved.
2. Heating to 50 °C and 70 °C — The undissolved baking soda dissolves on heating, and more can be added again.
3. Inference — Water at 70 °C dissolves more baking soda than at 50 °C or 20 °C; solubility of solids increases with temperature.
Conclusion: For most substances, solubility increases as temperature increases.

Introduction: Unlike solids, gases become less soluble in water as the temperature rises.
Key Points:
1. General rule — The solubility of gases in liquids generally decreases as temperature increases.
2. Cold water — More oxygen dissolves in cold water, ensuring sufficient oxygen for aquatic life.
3. Warm water danger — When water warms up, dissolved oxygen decreases, threatening fishes, plants, and other organisms.
Conclusion: Even the small amount of oxygen dissolved in water sustains all aquatic life.

Introduction: Concentration describes how much solute is present in a fixed quantity of solution or solvent.
Key Points:
1. Definition — Concentration is the amount of solute present in a fixed quantity of solution (or solvent).
2. Dilute vs concentrated — A dilute solution has less solute; a concentrated solution has more solute.
3. Relative terms — One spoon of salt in water is dilute compared with a solution of two or more spoons.
Conclusion: Dilute and concentrated are relative terms used to compare solutions.

Introduction: Density describes the heaviness of a substance in terms of its mass packed in a unit volume.
Key Points:
1. Definition — Density is the mass present in a unit volume of that substance.
2. Formula — Density = Mass / Volume; e.g., 16.400 g / 5 cm³ = 3.28 g/cm³.
3. Units — SI unit is kg/m³; for liquids, g/mL and g/cm³ are also commonly used.
Conclusion: Density allows us to compare how heavy different substances are for the same volume.

Introduction: Mass is the quantity of matter in an object and is measured using a balance.
Key Points:
1. Zero setting — Switch on the digital balance and press the tare or reset button to bring it to zero.
2. Watch glass — Place a dry, clean watch glass on the pan and reset the balance to zero again.
3. Reading — Place the object on the watch glass and note the reading, e.g., 16.400 g for a stone.
Conclusion: The tare button removes the container's mass so the balance shows only the object's mass.

Introduction: A measuring cylinder is a narrow transparent container with volume markings on its body.
Key Points:
1. Pouring — Place the cylinder on a flat surface and pour the liquid slowly up to the required mark.
2. Meniscus — The liquid forms a curved surface called the meniscus inside the cylinder.
3. Reading — For colourless liquids read the bottom of the meniscus; for coloured liquids read the top, keeping eyes level.
Conclusion: Correct eye position and meniscus reading give an accurate volume measurement.

Introduction: Volume is the space occupied by an object, and its measurement depends on the object's shape.
Key Points:
1. Regular shapes — For a cuboid, Volume = length × width × height; e.g., a notebook of 25 × 18 × 2 cm = 900 cm³.
2. Irregular shapes — Use the displacement method with a measuring cylinder filled with water.
3. Calculation — Volume of the object = final water level − initial water level; e.g., 55 − 50 = 5 cm³ for a stone.
Conclusion: Regular solids are measured by formula, irregular solids by displacement of water.

Introduction: Measuring cylinders of different capacities have different smallest readings, which decide accuracy.
Key Points:
1. Smallest readings — 10 or 25 mL cylinders read 0.1 mL; 100 mL reads 1 mL; 250 mL reads 2 mL; 500 mL reads 5 mL.
2. One-step measurement — The cylinder's capacity must exceed the volume needed, e.g., 70 mL needs at least a 100 mL cylinder.
3. Accuracy trade-off — Larger cylinders need fewer steps but are less accurate; a 100 mL cylinder is best for 70 mL.
Conclusion: Choose a cylinder whose capacity is just above the required volume for a one-step, accurate measurement.

Introduction: The density of a substance generally changes when it is heated or cooled.
Key Points:
1. Heating effect — On heating, particles move apart and spread, so the volume increases while mass stays the same.
2. Density change — Since Density = Mass / Volume, an increase in volume on heating decreases the density.
3. Hot air balloon — Hot air is less dense than the cool air around it, so it rises, lifting the hot air balloon.
Conclusion: Generally, density decreases with heating and increases with cooling.

Introduction: Pressure changes density differently for the three states of matter.
Key Points:
1. Gases — Increasing pressure pushes gas particles closer, decreasing volume and increasing density.
2. Liquids — Liquids are nearly incompressible, so pressure has only a small effect on their density.
3. Solids — Particles in solids are already very close, so changes in density under pressure are usually negligible.
Conclusion: Pressure affects the density of gases the most, and solids the least.

Introduction: Water shows the unusual property that its solid form, ice, is lighter than the liquid.
Key Points:
1. Maximum density at 4 °C — Water reaches its highest density at 4 °C, not at its freezing point.
2. Expansion on freezing — At 0 °C the particles rearrange into a structure taking more space, so volume increases and density decreases.
3. Protection of life — Floating ice forms a top layer that keeps the water underneath warm enough for fish and other creatures.
Conclusion: Ice floats because it is less dense than liquid water, and this helps aquatic life survive extreme cold.

Introduction: Whether an object floats or sinks in a liquid is decided largely by comparing densities.
Key Points:
1. Density decides — Objects less dense than water float, while denser objects sink; oil floats while an iron rod sinks.
2. Rice washing — Husk particles, being less dense, float, while rice, being denser, sinks to the bottom.
3. Bamboo rafts — Bamboo is light and hollow, so it floats easily and was used to make rafts in ancient times.
Conclusion: Floating or sinking is explained by the density of the object compared with the liquid.

Introduction: Relative density compares the density of a substance with the density of water.
Key Points:
1. Definition — Relative density = density of the substance / density of water at that temperature; it has no units.
2. Calculation — Density of sculpture = 225 g / 90 cm³ = 2.5 g/cm³, so relative density = 2.5 / 1 = 2.5.
3. Prediction — Since the sculpture is 2.5 times denser than water, it will sink in water.
Conclusion: Relative density is a unitless number that also predicts whether an object floats or sinks.

Hint: (a) ORS is a uniform mixture (solution); the components are evenly distributed throughout, so every sip has the same composition. (b) Solute(s) — sugar and salt; solvent — water. (c) No — chalk powder forms a non-uniform mixture whose components are not evenly distributed.

Hint: (a) A saturated solution — no more solute can dissolve and the excess settles at the bottom. (b) Heat the tea; solubility of solids increases with temperature, turning the saturated solution unsaturated. (c) Solubility is the maximum amount of sugar that dissolves in a fixed quantity of water (tea) at that temperature.

Hint: (a) The solubility of baking soda increases with temperature; water at 70 °C dissolves more than at 50 °C or 20 °C. (b) It behaves as an unsaturated solution, allowing more solute to dissolve. (c) Sodium hydrogen carbonate.

Hint: (a) Oxygen. (b) The solubility of gases decreases with temperature, so warm water holds less dissolved oxygen. (c) Cold water dissolves more oxygen, ensuring enough oxygen for fishes, plants, and other aquatic organisms.

Hint: (a) Water is the solvent and sugar is the solute. (b) It is surprising because water is present in a smaller amount, yet it is still the solvent. (c) It is a saturated solution, since no more sugar dissolves and any extra settles at the bottom.

Hint: (a) Place a watch glass on the digital balance, tare to zero, place the stone on it, and read 16.400 g. (b) Volume = 55 − 50 = 5 mL = 5 cm³, by the displacement method. (c) Density = 16.400 g / 5 cm³ = 3.28 g/cm³.

Hint: (a) A 100 mL measuring cylinder — it can hold 70 mL in one step and has a smaller smallest reading for better accuracy. (b) 1 mL. (c) The smallest reading of a 250 mL cylinder (2 mL) is greater, so it is less accurate.

Hint: (a) About 1000 g (since 1 mL of water ≈ 1 g). (b) Since 1 L of ghee (910 g) is lighter than 1 L of water (1000 g), ghee is less dense than water. (c) Ghee floats because it is less dense than water.

Hint: (a) Hot air is less dense than the surrounding cool air, so it rises and lifts the balloon. (b) On heating, particles move apart, volume increases, and density decreases. (c) On cooling, the air becomes denser again, so the balloon loses its lift and descends.

Hint: (a) The extremely high salt content (very high density) makes it difficult for aquatic organisms to survive. (b) Add salt to the water. (c) Adding salt increases the density of water beyond that of the egg, so the egg floats.

Introduction: A solution is a uniform mixture formed when one substance completely dissolves in another.
Key Points:
1. Definition — A solution is formed when a solute dissolves in a solvent to give a uniform mixture, like salt or sugar in water.
2. Solid-in-liquid — When a solid mixes with a liquid, the solid is the solute and the liquid is the solvent, as in salt water.
3. Two liquids — When two liquids form a solution, the smaller amount is the solute and the larger amount is the solvent, as in vinegar.
4. Chashni case — In gulab jamun syrup, water is still the solvent even though sugar is in a larger amount.
5. Solute + Solvent → Solution — Together the solute and solvent form the solution in which the solute is evenly distributed.
Conclusion: Identifying solute and solvent depends on physical state and, for two liquids, on the relative amounts.

Introduction: Solutions can be described by how much solute they contain and by their dissolving capacity.
Key Points:
1. Unsaturated solution — A solution that can still dissolve more solute at a given temperature.
2. Saturated solution — A solution in which no more solute dissolves; extra solute settles at the bottom at that temperature.
3. Concentration — The amount of solute present in a fixed quantity of solution or solvent.
4. Dilute vs concentrated — A dilute solution has less solute and a concentrated solution has more; the terms are relative.
5. Solubility — The maximum amount of solute that dissolves in a fixed quantity of solvent at a particular temperature.
Conclusion: These terms together describe both the present amount of solute and the dissolving limit of a solution.

Introduction: Temperature changes the solubility of substances differently depending on whether they are solids or gases.
Key Points:
1. Solids increase — For most solids, solubility increases with temperature, as seen with baking soda dissolving more at 70 °C than at 20 °C.
2. Saturated to unsaturated — A saturated solution at a lower temperature behaves as an unsaturated solution when heated.
3. Gases decrease — The solubility of gases in liquids generally decreases as temperature increases.
4. Oxygen in water — More oxygen dissolves in cold water than in warm water.
5. Aquatic life — Because warm water holds less oxygen, aquatic life suffers when water heats up in summer.
Conclusion: Temperature increases solubility for solids but decreases solubility for gases in liquids.

Introduction: Density is a property that describes the heaviness of a substance in terms of mass per unit volume.
Key Points:
1. Definition and formula — Density is the mass present in a unit volume; Density = Mass / Volume.
2. SI unit — The SI unit of density is kilogram per cubic metre (kg/m³).
3. Other units — For liquids, g/mL and g/cm³ are commonly used; 1 mL of water ≈ 1 g.
4. Relative density — Relative density = density of substance / density of water; it has no units.
5. Aluminium example — A 27 g aluminium block of volume 10 cm³ has density 2.7 g/cm³, so aluminium is 2.7 times denser than water (relative density 2.7).
Conclusion: Density and relative density let us compare the heaviness of different substances.

Introduction: The density of an irregular solid is found by measuring its mass and volume separately and dividing them.
Key Points:
1. Measure mass — Place a watch glass on a digital balance, press tare, place the object, and read the mass, e.g., 16.400 g.
2. Initial volume — Fill a measuring cylinder with water and note the initial level, e.g., 50 mL.
3. Displacement — Tie the object with a thread, lower it into the cylinder, and note the final level, e.g., 55 mL.
4. Calculate volume — Volume of the object = final − initial = 55 − 50 = 5 cm³.
5. Calculate density — Density = Mass / Volume = 16.400 g / 5 cm³ = 3.28 g/cm³.
Conclusion: Density of any irregular solid can be found by combining mass from a balance and volume by displacement.

Introduction: The volume of liquids is measured using a measuring cylinder, which must be chosen and read carefully.
Key Points:
1. Apparatus — A measuring cylinder is a narrow transparent cylinder with volume markings, available in sizes like 10, 25, 100, 250, and 500 mL.
2. Smallest readings — 10/25 mL read 0.1 mL, 100 mL reads 1 mL, 250 mL reads 2 mL, and 500 mL reads 5 mL.
3. Meniscus — The liquid forms a curved meniscus; read the bottom for colourless liquids and the top for coloured liquids.
4. Eye level — The eyes must be at the level of the bottom of the meniscus to avoid error.
5. Choice — A cylinder whose capacity is just above the required volume gives a one-step, accurate reading, like a 100 mL cylinder for 70 mL.
Conclusion: Accurate volume measurement depends on choosing the right cylinder and reading the meniscus correctly.

Introduction: Density depends on temperature and pressure, but the effects differ across the three states of matter.
Key Points:
1. Temperature effect — On heating, particles spread and volume increases while mass stays the same, so density decreases.
2. Hot air balloon — Hot air is less dense than cool air, so it rises and lifts a hot air balloon.
3. Pressure on gases — Increasing pressure pushes gas particles closer, decreasing volume and increasing density.
4. Pressure on liquids — Liquids are nearly incompressible, so pressure has only a small effect on their density.
5. Pressure on solids — Solid particles are already very close, so changes in density under pressure are usually negligible.
Conclusion: Density generally decreases with heating, and pressure affects gases the most and solids the least.

Introduction: Whether an object floats or sinks in a liquid depends mainly on comparing its density with the liquid's density.
Key Points:
1. General rule — Objects less dense than water float, while denser objects sink; oil floats, but an iron rod sinks.
2. Rice washing — Husk particles, being less dense, float, while rice, being denser, sinks to the bottom.
3. Bamboo rafts — Bamboo is light and hollow, so it floats easily and was used for rafts in ancient times.
4. Ice floats — At 0 °C water expands on freezing, so ice has a larger volume and lower density than liquid water.
5. Aquatic life — Floating ice forms a top layer that keeps the water underneath warm enough for aquatic life to survive.
Conclusion: Floating and sinking are explained by density differences between the object and the liquid.

Introduction: Although gases dissolve in water only to a small extent, the dissolved gases are vital for life.
Key Points:
1. Oxygen dissolves — Oxygen dissolves in water only to a small extent, yet this dissolved oxygen sustains all aquatic life.
2. Uniform mixture — Gases dissolve evenly in water, forming a uniform mixture, not a non-uniform one.
3. Temperature effect — The solubility of gases generally decreases as temperature increases, so cold water holds more oxygen.
4. Environmental concern — When lakes or ponds warm up, the dissolved oxygen drops, threatening fishes, plants, and organisms.
5. Everyday example — Aquatic species depend on dissolved oxygen, which is why cold, oxygen-rich waters support abundant aquatic life.
Conclusion: Even small amounts of dissolved gases are essential for aquatic life and environmental balance.

Introduction: Solutions and solvents play an important role in daily life, medicine, and Indian heritage.
Key Points:
1. ORS — Homemade ORS is a uniform mixture of sugar, salt, and water that keeps the body hydrated during dehydration.
2. Ayurveda and Siddha — Water has been the primary solvent for medicinal formulations in Ayurveda, Siddha, and other Indian systems.
3. Other solvents — Hydro-alcoholic extracts, oils, ghee, and milk are also used as solvents to obtain therapeutic benefits.
4. Asima Chatterjee — She used solvents and solutions to extract compounds from medicinal plants for anti-epileptic and anti-malarial drugs.
5. Ningel salt — In Manipur's Ningel village, salt is traditionally obtained by evaporating salt solution to form salt cakes wrapped in phanek cloth.
Conclusion: Solutions are central to medicine, daily life, and India's scientific and cultural heritage.
NCERT "Curiosity" Textbook | Chapters 10–13
Prepared for: Shipan Das
> Includes competency-based, application-style, and case-based questions as per CBSE guidelines.