Answer:

Muddy water is a suspension where the particles are larger (>1000 nm) and settle down due to gravity when left undisturbed. Milk is a colloid where the particles are smaller (1–1000 nm) and remain uniformly dispersed without settling because the particles are too small to be affected by gravity significantly.

Answer:

Evaporation occurs at the surface of a liquid at any temperature, while boiling occurs throughout the bulk of the liquid at a specific temperature called the boiling point. Evaporation is a slow process that happens at temperatures below the boiling point, whereas boiling is a rapid process that occurs when the vapour pressure equals atmospheric pressure.

Answer:

This happens due to the Tyndall effect. When sunlight passes through the gaps between leaves, it encounters dust and smoke particles present in the air. These particles scatter the light, making the path of the light beam visible as bright rays.

Answer:

Displacement becomes zero when the athlete returns to the starting point (reference point O).

Using Fig. 4.4: Starting from O, if the athlete runs from O to A (100 m), then back to B (60 m), and continues back to O (40 m more), the displacement will be zero.

Total distance travelled in that case = OA + AB + BO = 100 m + 60 m + 40 m = 200 m

So, displacement is zero but distance travelled is 200 m.

Answer:

Given: Volume of concentrate = 2 × 15 = 30 mL, Total volume of solution = 150 mL

Volume by volume percentage = (Volume of solute / Volume of solution) × 100

= (30 / 150) × 100 = 20% v/v

Therefore, the orange juice concentrate is 20% v/v in the mixture.

Answer:

To make vinegar from glacial acetic acid (100% acetic acid), you need to prepare a 5% v/v solution of acetic acid in water.

Procedure: Take 5 mL of glacial acetic acid and add it to enough water to make the total volume up to 100 mL. This will give a 5% v/v solution of acetic acid in water, which is vinegar.

Answer:

Answer: Compound 'B' is likely to deposit more solid.

Reason: From the solubility curves, compound B has a steeper slope between 80°C and 60°C, meaning its solubility decreases more rapidly with temperature. Therefore, on cooling, more of compound B will come out of solution compared to compound A.

Answer:

Answer: Yes, the size of common salt crystals will change.

Explanation:

• Slow evaporation: Allows particles more time to arrange themselves in a regular pattern, resulting in larger, well-formed crystals.
• Fast evaporation: Particles do not get enough time to arrange properly, resulting in smaller, less well-formed crystals.

Answer:

(i) True – Salt can be separated from a salt solution by evaporation (to get salt) or distillation (to get pure water).

(ii) False – Distillation cannot be used when two liquids have the same boiling point. Correction: Distillation works only when liquids have a difference of at least 25°C in their boiling points.

(iii) False – The solvent level should be below the sample spot. Correction: In paper chromatography, the solvent level should be below the sample spot so that the sample moves up with the solvent.

(iv) False – Evaporation and crystallization are not the same. Correction: Evaporation removes the solvent completely, while crystallization involves slow cooling of a saturated solution to form pure crystals.

Answer:

Immiscible liquids form two separate layers because they have different densities. The liquid with higher density settles at the bottom, while the liquid with lower density forms the upper layer. They do not mix with each other.

Answer:

Yes, sublimation is different from evaporation.

• Evaporation: Liquid changes to vapour at any temperature below its boiling point. It involves the liquid state.
• Sublimation: Solid changes directly to vapour without passing through the liquid state.

In sublimation, the substance goes from solid to gas directly (e.g., camphor, naphthalene, dry ice).

Answer:

Clouds are a colloid.

Reason: The tiny water droplets or ice crystals (dispersed phase) are suspended in air (dispersion medium). The particles are between 1–1000 nm in size, do not settle down easily, and scatter light (Tyndall effect). This makes clouds a colloidal mixture.

Answer:

Cities with a lot of smoke and dust look hazy because of the Tyndall effect. The smoke and dust particles suspended in the air scatter sunlight, making the air appear hazy or foggy. This scattering of light by particles in a colloid or suspension is the Tyndall effect.

Answer:

Completed Table 5.1:

Answer:

The correct option is (iv) Muddy water-Ht, Milk-Ht, Blood-Ht, Brass-Hm.

Explanation:

• Muddy water – Heterogeneous (suspension)
• Milk – Heterogeneous (colloid)
• Blood – Heterogeneous (colloid)
• Brass – Homogeneous (alloy – solid solution)

Option (i) is incorrect because Smoke is heterogeneous. Option (ii) is incorrect because Vinegar is homogeneous and Brass is homogeneous. Option (iii) is incorrect because Milk is heterogeneous.

Answer:

The correct option is (iii) a and c.

Explanation:

• (a) Air and dust particles – Heterogeneous mixture (suspension) – shows Tyndall effect.
• (b) Copper sulfate and water – Homogeneous solution – does not show Tyndall effect.
• (c) Starch and water – Colloid – shows Tyndall effect.
• (d) Acetone and water – Homogeneous solution – does not show Tyndall effect.

Option (a) is incorrect because copper sulfate solution does not show Tyndall effect. Option (b) is incorrect because both are solutions. Option (d) is incorrect because acetone and water is a solution.

Answer:

Answer:

(i) Total mass of mixture = 75 + 420 + 5 = 500 g

• Sugar % = (75/500) × 100 = 15% m/m
• Flour % = (420/500) × 100 = 84% m/m
• Sodium hydrogencarbonate % = (5/500) × 100 = 1% m/m

(ii) Brass contains 70% copper and 30% zinc.

• Mass of copper = (70/100) × 120 = 84 g
• Mass of zinc = (30/100) × 120 = 36 g

Answer:

• Oil and water are immiscible, so they will form separate layers.
• Since the density of oil is less than water, oil will form the upper layer and water will form the lower layer.
• They can be separated using a separating funnel.

Procedure: Pour the mixture into a separating funnel. Let it stand until two layers form. Open the stopcock to drain the lower layer (water). Close the stopcock when water is almost drained. Collect the oil layer separately.

Answer:

The correct option is (iii) A is true, but R is false.

Explanation:

• Assertion is true: Solutions do not exhibit the Tyndall effect because the particles are too small to scatter light.
• Reason is false: The particles in solutions are less than 1 nm in size, not larger than 100 nm. It is the particles in colloids and suspensions that scatter light.

Answer:

Answer:

Method: Distillation

Reason: The boiling points of A and B differ by 30°C (difference > 25°C), so they can be separated by simple distillation.

Process: Heat the mixture in a distillation flask. Liquid A (boiling point 60°C) vaporises first. The vapour passes through a condenser where it cools and becomes liquid A, collected in a separate vessel. Liquid B remains in the distillation flask.

Diagram: A distillation setup consists of:

• Distillation flask (with mixture and boiling chips)
• Thermometer (to monitor temperature)
• Condenser (with water inlet and outlet)
• Receiver (to collect the distillate)

Answer:

Comparison of Evaporation, Crystallization and Distillation:

Preference:

• Evaporation: When only the solid solute is needed and the solvent is not required.
• Crystallization: When pure crystals of a substance are needed (e.g., sugar, copper sulfate).
• Distillation: When both components need to be recovered or when the solvent is valuable (e.g., obtaining pure water from salt solution).

Answer:

(i) If blood behaved like a true suspension:

• The blood cells would settle down due to gravity inside the body.
• This would block blood vessels and prevent proper circulation.
• Oxygen and nutrients would not be transported effectively.
• The body would not be able to function properly, leading to serious health issues.

(ii) In a blood sample:

• Dispersed phase: Blood cells (RBCs, WBCs, platelets)
• Dispersion medium: Plasma (liquid component)

Answer:

Correct sequence of separation techniques:

1. Sublimation – To separate naphthalene from the mixture. Naphthalene sublimes and gets deposited on the inner walls of the funnel.
2. Dissolution in water + Filtration – Add water to the remaining mixture (sand + salt). Salt dissolves in water, sand does not. Filter to separate sand (residue) from salt solution (filtrate).
3. Evaporation – Heat the salt solution to evaporate water and obtain pure salt crystals.

Answer:

Distillation is effective for separating water and acetone because:

• Difference in boiling points: Acetone boils at 56°C, while water boils at 100°C. The difference (44°C) is greater than 25°C, making simple distillation suitable.
• When the mixture is heated, acetone (lower boiling point) vaporises first and is collected as distillate, while water remains in the distillation flask.

Answer:

(i) Mass of potassium nitrate needed at 40°C:

• At 40°C, solubility of KNO₃ = 62 g per 100 g water
• For 50 g water = (62/100) × 50 = 31 g

(ii) Observation when cooling saturated KCl solution:

• At 80°C, solubility of KCl = 54 g per 100 g water
• At 25°C (between 20°C and 30°C), solubility ≈ 36 g per 100 g water
• As the solution cools, excess KCl will crystallize out because solubility decreases with temperature.

(iii) Effect of temperature on solubility:

• For most solid solutes, solubility increases with increase in temperature.
• Comparison (10°C to 80°C):
• Potassium nitrate: Large increase (21 → 167 g) – steep increase
• Ammonium chloride: Moderate increase (24 → 66 g)
• Potassium chloride: Moderate increase (35 → 54 g)
• Sodium chloride: Very slight increase (36 → 37 g) – almost constant

Answer:

(i) Mass percentage calculations:

• Student A: Mass of solution = 20 + 80 = 100 g; % = (20/100) × 100 = 20% m/m
• Student B: Mass of solution = 20 + 100 = 120 g; % = (20/120) × 100 = 16.67% m/m
• Student C: Mass of solution = 30 + 80 = 110 g; % = (30/110) × 100 = 27.27% m/m

(ii) Most concentrated solution: Student C's solution (27.27% m/m)

Reason: Student C has the highest mass of sugar (30 g) per total mass of solution (110 g), resulting in the highest mass percentage. Even though Student C used the same amount of water as Student A, they used more sugar, making it more concentrated.

Answer:

(i) Separation technique marked as 'S': Distillation

(ii) Labelling of apparatus:

• A – Distillation flask (containing the mixture)
• B – Condenser (with water inlet and outlet)
• C – Receiver (collecting the distillate)

(iii) Mixtures that can be separated by distillation:

• (a) water - acetone – Yes (BP difference = 100 − 56 = 44°C > 25°C)
• (b) water - salt – No (distillation can separate but here salt is solid, not liquid)
• (c) acetone - alcohol – No (BP difference = 78 − 56 = 22°C < 25°C, so fractional distillation would be needed)
• (d) sand - salt – No (solid-solid mixture, not suitable)
• (e) alcohol - chloroform – No (BP difference = 78 − 61 = 17°C < 25°C, fractional distillation needed)
• (f) alcohol - benzene – No (BP difference = 80 − 78 = 2°C < 25°C, fractional distillation needed)

Correct answer for simple distillation: Only (a) water - acetone has difference > 25°C.

Answer:

This is an experiential activity.

Procedure:

1. Take three transparent beakers containing: (a) salt solution (true solution), (b) milk + water (colloid), (c) chalk powder + water (suspension).
2. Shine a laser pointer or flashlight through each beaker.
3. Observe from the side.
4. Observation: The beam is visible in milk (colloid) and chalk suspension, but not in salt solution.
5. Conclusion: Colloids and suspensions show the Tyndall effect because particles scatter light.

Safety: Never look directly into the laser beam.

Answer:

This is an experiential activity.

Procedure:

1. Prepare saturated solutions of different compounds in separate beakers.
2. Filter each solution and allow them to cool slowly.
3. Observe the crystals formed under a magnifying glass or microscope.
4. Observations:
• Common salt (NaCl): Colourless, cubic crystals
• Epsom salt (MgSO₄): Colourless, needle-like crystals
• Sugar (C₁₂H₂₂O₁₁): Colourless, monoclinic crystals
• Copper sulfate (CuSO₄): Blue, triclinic crystals
• Borax: Colourless, monoclinic crystals
5. Note down the colour and shape of each crystal.

Answer:

This is an experiential activity.

Procedure:

1. Collect red leaves (e.g., from poinsettia or red maple).
2. Grind the leaves with a small amount of alcohol to extract pigments.
3. Apply a drop of the extract on a filter paper strip (2 cm from bottom).
4. Place the strip in a beaker containing a solvent (alcohol/water mixture).
5. Observe after 15-20 minutes.
6. Observation: The pigments separate into different bands – you may see green (chlorophyll) along with red/other pigments.
7. Conclusion: Red leaves also contain green pigments (chlorophyll) hidden by other pigments.

Answer:

This is an experiential activity.

Procedure for food colour:

1. Take a filter paper strip and draw a pencil line 2 cm from bottom.
2. Place a small drop of food colour on the line.
3. Dip the strip in a beaker with water (solvent level below the spot).
4. Observe as the solvent rises.
5. Observation: Different colours separate based on solubility.

For coloured mouth fresheners: Crush the fennel seeds, extract with a few drops of water, and apply the extract on the paper. Run chromatography to see the number of components.

Answer:

This is a project activity.

Game Idea – "Separate It!"

• Objective: Players identify the correct separation technique for different mixtures.
• Materials: Cards with mixture names, cards with separation techniques, timer, scoreboard.
• Gameplay:
  • Each player draws a mixture card (e.g., "Salt and Water", "Oil and Water", "Sand and Iron Filings").
  • They must select the correct separation technique from the technique cards.
  • Explain the reason for their choice.
  • Score points for correct answers and good explanations.
• Learning Outcome: Students understand the principles of different separation techniques.

Answer:

This is a practical/experiential activity.

Simple distillation setup using camping items:

• Items: Metal pot/cup, lid, small container, fire source, stones, cloth.
• Procedure:
  1. Place the muddy/salty water in a metal pot.
  2. Heat the pot over a fire.
  3. Place a small container inside the pot to collect clean water.
  4. Cover the pot with a lid (inverted) so that steam condenses on it.
  5. Collect the condensed water droplets in the container.
• Alternative: Use a plastic sheet stretched over the pot to collect condensed water.

Answer:

This is a thought-provoking/question-based activity.

Current status: Scientists are working on developing artificial blood substitutes that can carry oxygen and perform some functions of real blood.

Challenges:

• Blood is a complex colloid with multiple components (RBCs, WBCs, platelets, plasma).
• Artificial blood must be compatible with all blood types.
• It must carry oxygen, fight infections, and clot properly.
• It should not cause immune reactions.

Advantages if possible:

• No need for blood type matching.
• Can be stored longer than real blood.
• Can be produced in large quantities.
• Reduces dependency on blood donors.

Current research: Scientists are exploring hemoglobin-based oxygen carriers (HBOCs) and perfluorocarbon-based blood substitutes. However, challenges remain regarding safety and effectiveness.

1. A student prepares four mixtures and observes them after stirring. Which mixture is most likely to be homogeneous?
(a) flour mixed with water (b) lemon juice mixed with water (c) soil mixed with water (d) rice grains mixed with pulses
Answer: (b) lemon juice mixed with water

2. Which of the following mixtures can best be separated using centrifugation?
(a) Sand and water (b) Ink pigments (c) Cream and milk (d) Salt and sugar
Answer: (c) Cream and milk

3. When a hot saturated solution is cooled, crystals form because:
(a) Solubility decreases (b) Density increases (c) Boiling point decreases (d) Colour changes
Answer: (a) Solubility decreases

4. In paper chromatography, different dyes in black ink move different distances on the paper. This separation occurs mainly because dyes differ in:
(a) Density (b) Adsorption and solubility (c) Magnetic properties (d) Particle size
Answer: (b) Adsorption and solubility

5. Distillation separates substances based on:
(a) Density (b) Solubility (c) Boiling point difference (d) Particle size
Answer: (c) Boiling point difference

6. A chemist needs to separate iodine from sand. Which technique is most appropriate?
(a) Chromatography (b) Sublimation (c) Centrifugation (d) Crystallisation
Answer: (b) Sublimation

7. A chemist wants to analyze pigments in plant leaves. Which method is most appropriate?
(a) Distillation (b) Paper chromatography (c) Centrifugation (d) Coagulation
Answer: (b) Paper chromatography

8. In water purification, alum is added to muddy water causing suspended particles to settle quickly. Which process is involved?
(a) Distillation (b) Coagulation (c) Chromatography (d) Sublimation
Answer: (b) Coagulation

9. Simple distillation is effective only when:
(a) Density difference is large (b) Boiling point difference is large (~25°C or more) (c) Solubility is same (d) Liquids are immiscible
Answer: (b) Boiling point difference is large (~25°C or more)

10. A solubility graph shows that the solubility of a salt increases sharply with temperature. Which method would be most suitable to purify this salt?
(a) Centrifugation (b) Crystallisation (c) Sublimation (d) Chromatography
Answer: (b) Crystallisation

11. What is solubility?
(a) Amount of solvent in a solution (b) Maximum amount of solute that dissolves in a solvent at a given temperature (c) Amount of solution formed (d) Rate of dissolving
Answer: (b) Maximum amount of solute that dissolves in a solvent at a given temperature

12. Which concentration method is most suitable when a solid solute is dissolved in a liquid and the final solution is measured in millilitres?
(a) Mass by mass percentage (b) Mass by volume percentage (c) Volume by volume percentage (d) Density percentage
Answer: (b) Mass by volume percentage

13. A beam of light is passed through four mixtures. In which mixture will the path of light not be visible?
(a) soap solution with tiny oil droplets (b) starch mixed with water (c) clear glucose solution (d) smoke-filled air
Answer: (c) clear glucose solution

14. Which of the following correctly matches the mixture with its separation method?
(a) Cream from milk – Separating funnel (b) Blood components – Centrifugation (c) Salt solution – Sublimation (d) Oil and water – Chromatography
Answer: (b) Blood components – Centrifugation

15. Which pair is correctly matched?
(a) Solution – particles visible to naked eye (b) Suspension – particles do not settle (c) Colloid – particles scatter light (d) Solution – particles separated by ordinary filtration
Answer: (c) Colloid – particles scatter light

Direction: In the following questions, two statements are given — one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (a), (b), (c), (d) as given below:
(a) Both A and R are correct and R is the correct explanation of A.
(b) Both A and R are correct but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

16. Assertion (A): The liquid collected during distillation is called distillate.
Reason (R): Vapours formed during heating condense to form liquid again.
Answer: (a) Both are correct and R explains A.

17. Assertion (A): Rapid cooling during crystallisation may produce impure crystals.
Reason (R): Rapid crystal formation traps impurities within the crystal lattice.
Answer: (a) Both are correct and R explains A.

18. Assertion (A): Sublimation can separate ammonium chloride from sand.
Reason (R): Sand sublimes at a higher temperature than ammonium chloride.
Answer: (c) A is true but R is false. (Sand does not sublime.)

19. Assertion (A): A centrifuge machine rotates samples at high speed.
Reason (R): Rotation produces centrifugal force, which separates particles.
Answer: (a) Both are correct and R explains A.

20. Assertion (A): A saturated solution cannot dissolve more solute at a given temperature.
Reason (R): It already contains the maximum amount of solute possible at that temperature.
Answer: (a) Both are correct and R explains A.

Answer:

Correct option: (b) A, B and D only

Explanation:

• (A) Correct: Both substances will crystallize out because solubility decreases as temperature drops from 80°C to 20°C.
• (B) Correct: Substance A will crystallize out in a significantly larger quantity than Substance B because its solubility decreases much more sharply with temperature.
• (C) Incorrect: The solubility of B does not remain relatively constant; it decreases significantly. Therefore, a considerable amount of B will also solidify.
• (D) Correct: At 20°C, Substance B is more soluble in water than Substance A (the curve for B is higher than A at 20°C).

Answer:

Most suitable technique: Simple Distillation

Justification: The boiling point difference between A (56°C) and B (100°C) is 44°C, which is greater than 25°C. Therefore, simple distillation can effectively separate the two miscible liquids based on their difference in boiling points. Liquid A will vaporise first and can be collected separately, leaving liquid B behind.