The chapter Exploring Mixtures and Their Separation helps students understand why substances mix differently and how the components of mixtures can be separated. The concepts are closely connected with everyday experiences such as filtering tea, separating oil from water, obtaining salt from seawater, purifying liquids and separating colours from ink.
On this page, students can revise the major concepts of the chapter and understand the logic behind important textbook questions. The explanations focus on solutions, suspensions, colloids, concentration, solubility and separation techniques.
Quick Chapter Overview
| Topic | Key Idea |
|---|---|
| Mixture | Physical combination of two or more substances |
| Homogeneous mixture | Uniform composition throughout |
| Heterogeneous mixture | Non-uniform composition |
| Solution | Homogeneous mixture with very small particles |
| Suspension | Heterogeneous mixture whose particles may settle |
| Colloid | Mixture with dispersed particles that remain distributed |
| Tyndall effect | Scattering of light by sufficiently large dispersed particles |
| Distillation | Separation using difference in boiling points |
| Crystallization | Formation of pure solid crystals from a solution |
| Chromatography | Separation based on different movement of components |
| Sublimation | Direct solid-to-vapour change for suitable substances |
Important Formulas
Mass by Mass Percentage
Mass by Volume Percentage
Volume by Volume Percentage
Concentration of Solutions
For numerical problems, students should first identify whether concentration is expressed using mass or volume.
Mass percentage
Mass percentage = (Mass of solute ÷ Mass of solution) × 100
Volume percentage
Volume percentage = (Volume of solute ÷ Volume of solution) × 100
Mass by volume percentage
Mass by volume percentage = (Mass of solute in g ÷ Volume of solution in mL) × 100
Questions & Step-by-step Solutions with Explanation
Think It Over
1. Why do suspended particles settle in muddy water over time but not in milk?
Muddy water is a suspension. Its solid particles are comparatively large and sufficiently heavy to settle under gravity when the mixture is left undisturbed.
Milk behaves as a colloid. Its dispersed particles are much smaller and remain distributed throughout the dispersion medium. Therefore, they do not settle easily under normal conditions.
Key idea: Particle size and stability distinguish a suspension from a colloid.
2. How is evaporation different from boiling?
Evaporation is a surface phenomenon and can occur below the boiling point. Only some molecules at the surface acquire enough energy to escape into the vapour phase.
Boiling occurs throughout the liquid at a definite temperature for a given pressure. Vapour bubbles form inside the liquid and rise to the surface.
| Evaporation | Boiling |
|---|---|
| Surface phenomenon | Bulk phenomenon |
| Can occur at different temperatures | Occurs at boiling point at fixed pressure |
| Usually slow | Usually rapid |
| No bubble formation throughout liquid | Bubbles form throughout liquid |
3. Why do you see bright rays of sunlight when it passes through small gaps between the leaves of a dense tree?
The air contains fine dust, smoke, moisture droplets and other small dispersed particles. When sunlight passes through such a region, these particles scatter light.
This scattering makes the path of the beam visible. The phenomenon is related to the Tyndall effect.
Pause and Ponder
1. A common talcum powder contains 4 % m/m zinc oxide, which acts as an antiseptic. How much zinc oxide is present in 300 g of the talcum powder?
A powder contains 4% zinc oxide by mass. For 300 g of powder:
Mass of zinc oxide
= 4/100 × 300
= 12 g
Therefore, 300 g of the powder contains 12 g of zinc oxide.
2. Your mother gives you a bottle of orange juice concentrate to mix with water and serve it to your visiting friends. She asks you to mix two tablespoons of the concentrate with water in a glass tumbler. If each tablespoon measures 15 mL and you make 150 mL of juice per person, what is the % v/v of orange juice concentrate in the mixture you prepared?
Two tablespoons of concentrate are used.
Volume of one tablespoon = 15 mL
Therefore:
Volume of concentrate = 2 × 15 = 30 mL
Final volume of prepared drink = 150 mL
Volume percentage:
= 30/150 × 100
= 20% v/v
Therefore, the prepared drink contains 20% concentrate by volume.
3. Vinegar, used as a food preservative and additive, contains 5 % v/v acetic acid. Glacial acetic acid is a liquid, i.e., 100% acetic acid. If you want to make vinegar from glacial acetic acid, how would you proceed?
To prepare a dilute solution from concentrated acetic acid, the required amount of concentrated acid is measured and diluted carefully with water until the desired final volume is obtained.
For example, for a final volume of 100 mL at 5% v/v, the mixture requires:
- 5 mL acetic acid
- enough water to make the final total volume 100 mL
For laboratory preparation, appropriate safety precautions and supervised handling are essential because concentrated acetic acid can be hazardous.
4. Refer to the solubility curves given in Activity 5.2. If equal masses of hot, saturated solutions of compounds ‘A’ and ‘B’ are cooled from 80 °C to 60 °C, which solution is likely to deposit more solid?
A saturated solution contains the maximum amount of solute that can dissolve under specified conditions.
When a hot saturated solution cools, the solubility of many solids decreases. The excess dissolved substance may then separate as crystals.
The amount deposited depends on the change in solubility between the initial and final temperatures. Therefore, when comparing substances using solubility curves, students should compare the decrease in solubility over the given temperature interval rather than only the absolute solubility at one temperature.
5. Will there be any change in the size of common salt crystals if the rate of evaporation is increased or decreased? Explain.
Yes. Slow evaporation generally provides more time for particles to arrange into an orderly crystal structure, producing larger crystals.
Rapid evaporation generally promotes the formation of smaller crystals.
6. State whether the following statements are True or False. Also, correct the False statements.
(i) Salt can be separated from a salt solution by evaporation or distillation.
(ii) Distillation can be used for separation of two liquids even when these have the same boiling point.
(iii) In paper chromatography, the solvent level should be above the sample spot at the beginning of the experiment.
(iv) Evaporation and crystallization are the same processes.
Salt can be recovered from salt solution by evaporation.
True. Water evaporates and the non-volatile salt remains.
Distillation can separate any two liquids even if their boiling points are identical.
False. Ordinary distillation depends on sufficient difference in volatility or boiling behaviour.
The solvent level should initially cover the sample spot in paper chromatography.
False. The spot should remain above the initial solvent level; otherwise, the sample may dissolve directly into the solvent reservoir.
Evaporation and crystallization are identical.
False. Evaporation removes solvent, whereas crystallization is used to obtain comparatively pure crystals under controlled conditions.
7. Why do immiscible liquids form two separate layers in a separating funnel?
Immiscible liquids do not mix uniformly because their molecular interactions do not favour mixing.
When placed in a separating funnel, they form separate layers. Their relative positions depend mainly on density: the denser liquid generally forms the lower layer.
A separating funnel allows the lower layer to be drained first through the stopcock.
8. Is sublimation different from evaporation? Justify.
Sublimation is the direct conversion of a solid into vapour without passing through the liquid state under the relevant conditions.
Evaporation is the escape of molecules from the surface of a liquid into the gaseous state.
Examples of substances commonly discussed in school-level sublimation experiments include camphor and naphthalene.
9. Clouds are made up of tiny water droplets or ice crystals floating in the air. Based on what you know about solutions, suspensions and colloids, what type of mixture do you think clouds are and why?
Solution, Colloid and Suspension Comparison
| Property | Solution | Colloid | Suspension |
|---|---|---|---|
| Nature | Homogeneous | Apparently uniform but microscopically heterogeneous | Heterogeneous |
| Particle size | Very small | Intermediate | Comparatively large |
| Settling | No | Normally no | Usually yes |
| Ordinary filtration | Not separated | Not separated by ordinary filtration | Often separable |
| Tyndall effect | Generally absent | Present | Light may be strongly scattered |
10. Why do cities with a lot of smoke and dust in the air often look hazy?
Revise, Reflect, Refine
Question 1
Which of the following mixtures are correctly classified as homogeneous (Hm) and heterogeneous (Ht)? Choose the correct option.
(i) Air — Hm, Milk — Ht, Sugar solution — Hm, Smoke — Hm
(ii) Brass — Ht, Fog — Ht, Vinegar — Ht, Muddy water — Hm
(iii) Copper sulfate solution — Hm, Salt solution — Hm, Milk — Hm, Bronze — Hm
(iv) Muddy water — Ht, Milk — Ht, Blood — Ht, Brass — Hm
Answer
Understand the reason behind classification rather than memorize isolated lists.
Homogeneous examples: air under normal conditions, salt solution, sugar solution, brass.
Heterogeneous or dispersed-system examples: muddy water, milk, smoke, fog and blood at the appropriate level of description.
Milk is a colloidal system, while muddy water behaves as a suspension.
Question 2
Choose the correct options, and explain the reason for the correct and
incorrect options.
Which among the following mixtures show the Tyndall Effect?
A mixture of:
(a) air and dust particles
(b) copper sulfate and water
(c) starch and water
(d) acetone and water
(i) a and b (ii) b and d (iii) a and c (iv) c and d
Answer
A true solution such as copper sulfate dissolved completely in water does not normally show the Tyndall effect because its particles are too small to scatter visible light sufficiently.
Mixtures containing fine dispersed particles, such as starch dispersion and dusty air, can scatter light.
Therefore, when solving such MCQs, first classify the mixture as a true solution, colloid or suspension.
Question 3
A mixture can be categorised as a solution, a suspension, or a colloid, each possessing distinct properties. Utilise the words or phrases provided in the box to fill in the following Table . Words and phrases may be used more than once.
Question 4 (i)
Solve the following problems:
(i) A cake recipe uses dry ingredients, namely 75 g of sugar for 420 g of all-purpose flour and 5 g of sodium hydrogencarbonate. Express the concentration of each component in the mixture using
an appropriate method.
(ii) A brass alloy contains 70% copper by mass. Calculate the quantities
of copper and zinc present in 120 g of brass.
Suppose 120 g of brass contains 70% copper by mass.
Copper:
= 70/100 × 120
= 84 g
Remaining zinc:
= 120 − 84
= 36 g
Therefore, the alloy contains:
Copper = 84 g
Zinc = 36 g
Question 5
The label on a cooking oil pack says one litre (910 g). If this oil is mixed with water, will it form a separate layer? If so, which substance will be on top? How will you separate the two layers? Also, draw the diagram of the apparatus used.
Answer
Oil and water are immiscible and form separate layers. If the oil is less dense than water, it forms the upper layer.
The appropriate apparatus is a separating funnel.
Procedure:
- Transfer the mixture to the separating funnel.
- Allow the two layers to separate completely.
- Open the stopcock carefully.
- Collect the lower aqueous layer.
- Close the stopcock near the boundary.
- Collect the remaining upper layer separately.
Question 6
Assertion (A): Solutions do not exhibit the Tyndall effect.
Reason (R): The particles in solutions are larger than 100 nm, so they
cannot scatter light.
Choose the correct option:
(i) Both A and R are true, and R is the correct explanation of A.
(ii) Both A and R are true, but R is not the correct explanation of A.
(iii) A is true, but R is false.
(iv) A is false, but R is true.
The statement that true solutions do not show the Tyndall effect is correct.
However, saying that solution particles are larger than 100 nm is incorrect. True-solution particles are extremely small and therefore do not scatter visible light sufficiently.
Hence, for the assertion–reason item on the page, the correct logic is:
Assertion true, Reason false.
Question 7
How would you separate the mixtures given in Table 5.3? Mention the reason for choosing your method. If a mixture cannot be separated, explain why
Choose a separation method based on a measurable difference in physical properties.
| Difference in Property | Suitable Method |
|---|---|
| Particle size | Filtration or sieving |
| Density of immiscible liquids | Separating funnel |
| Boiling point or volatility | Distillation |
| Ability to sublime | Sublimation |
| Solubility and crystal formation | Crystallization |
| Different movement between stationary and mobile phases | Chromatography |
| Fine dispersed particles | Centrifugation in suitable cases |
The method should always be justified by explaining which physical property differs.
Question 8
Two miscible liquids, A and B, are present in a mixture. The boiling point of A is 60 °C and the boiling point of B is 90 °C. Suggest a method to separate them. Also, draw a labelled diagram of the method
suggested.
If two miscible liquids have sufficiently different boiling points, distillation can be used.
The more volatile component vaporizes preferentially. The vapour passes through a condenser, where it cools and changes back into liquid. The distillate is collected separately.
For liquids with closer boiling points, fractional distillation may be more appropriate.
Question 9
Compare evaporation, crystallization and distillation. In which situation, would you prefer each of these over the others?
Evaporation
Use evaporation when the main objective is to recover a non-volatile dissolved solid and recovery of the solvent is not required.
Crystallization
Use crystallization when a comparatively pure crystalline solid is desired. It can help separate crystals from certain soluble impurities.
Distillation
Use distillation when the solvent must be recovered or when suitable volatile liquid components need to be separated based on differences in volatility.
Question 10
Blood is an example of a colloidal mixture. (i) What would happen if blood behaved like a true suspension inside the body? (ii) In a blood sample, identify the dispersed phase and the dispersion medium.
If blood behaved like an unstable suspension whose particles rapidly settled under gravity, uniform transport through the circulatory system would be severely disrupted.
At school level, blood is often discussed as a complex colloidal/dispersed system. Its liquid portion acts as the continuous medium, while cells and other components are distributed through it.
Students should follow the terminology used in their prescribed textbook when answering examination questions.
Question 11
You are given a mixture of sand, common salt and naphthalene (Fig. 5.25a). The Fig. 5.25b depicts various steps used to separate the components of this mixture. Identify and write down the correct
sequence of separation techniques
A logical separation sequence uses differences in physical properties.
First, naphthalene can be separated using its tendency to sublime under suitable conditions.
Next, water can be added to the remaining sand-and-salt mixture. Salt dissolves, whereas sand does not.
The sand is then separated by filtration.
Finally, salt is recovered from the filtrate by evaporation or crystallization.
The key principle is:
Sublimation → selective dissolution → filtration → evaporation/crystallization
Question 12
Why is distillation an effective method for separating a mixture of water and acetone?
Water and acetone are miscible, so filtration or a separating funnel cannot separate them.
They differ substantially in volatility and boiling behaviour. On controlled heating, the more volatile component vaporizes preferentially and is condensed and collected.
Therefore, distillation is suitable for their separation.
Question 13
Answer the following questions with the help of the data given in Table 5.4.
(i) What mass of potassium nitrate would be needed to prepare its saturated solution in 50 g of water at 40 °C?
(ii) A student makes a saturated solution of potassium chloride in water at 80 °C and leaves the solution to cool at room temperature (25 °C). What would she observe as the solution cools? Explain.
(iii) What is the effect of a change in temperature on the solubility of salts? Also, compare the changes in the solubility of the four given salts with increasing temperature from 10 °C to 80 °C.
Question 14 (i)
Three students, A, B and C, are preparing sugar solutions for an experiment:
Student A dissolves 20 g of sugar in 80 g of water.
Student B dissolves 20 g of sugar in 100 g of water.
Student C dissolves 30 g of sugar in 80 g of water.
- Calculate the mass percentage (% m/m) concentration of sugar in
each student’s solution. - Whose solution is the most concentrated? Explain why.
For a solution containing 20 g sugar and 80 g water:
Total mass = 100 g
Sugar concentration = 20%
For 20 g sugar and 100 g water:
Total mass = 120 g
Concentration = 20/120 × 100
= 16.67%
For 30 g sugar and 80 g water:
Total mass = 110 g
Concentration = 30/110 × 100
≈ 27.27%
Therefore, the third solution is the most concentrated.
Question 15
Examine Fig. 5.26.
1. Identify the separation technique marked as ‘S’.
2. Label the apparatus A, B and C.
3. Which of the following mixtures can be separated by the technique identified above? Use the data given in Table 5.5. Mixtures:
(a) water — acetone
(b) water — salt
(c) acetone — alcohol
(d) sand — salt
(e) alcohol — chloroform (f) alcohol — benzene
Common Mistakes to Avoid
Students frequently confuse a colloid with a true solution because both may appear uniform to the naked eye. Another common error is selecting filtration for dissolved substances; ordinary filtration cannot remove dissolved salt from water.
In numerical questions, always check whether the denominator should be mass of solution or volume of solution. For separation questions, do not write only the method name—explain the physical property that makes the method suitable.
Students should also distinguish carefully between evaporation, crystallization, simple distillation and fractional distillation.
Exam Tips
For examination preparation, focus on understanding the reason behind each separation technique. Learn the differences among solution, colloid and suspension through a comparison table rather than isolated definitions.
Practice concentration numericals regularly, especially mass percentage and volume percentage. In apparatus-based questions, draw clean diagrams with meaningful labels. When answering reasoning questions, connect the observation with particle size, solubility, density, boiling point or volatility.
Practice MCQs
1. Which system commonly shows the Tyndall effect?
A. Salt solution
B. Sugar solution
C. Milk
D. Copper sulfate solution
Answer: C. Milk
2. Which apparatus is suitable for separating two immiscible liquids?
A. Separating funnel
B. Filter paper only
C. Evaporating dish
D. Chromatography paper
Answer: A. Separating funnel
3. Which property is mainly used in distillation?
A. Colour
B. Difference in volatility or boiling behaviour
C. Shape
D. Magnetic property only
Answer: B. Difference in volatility or boiling behaviour
4. Which method is useful when a solid changes directly into vapour?
A. Filtration
B. Sublimation
C. Sedimentation
D. Decantation
Answer: B. Sublimation
5. Why does muddy water settle on standing?
A. It is a true solution
B. Its particles are comparatively large and affected by gravity
C. Water evaporates instantly
D. The particles dissolve completely
Answer: B. Its particles are comparatively large and affected by gravity
Frequently Asked Questions
What is the main difference between a solution and suspension?
A solution contains particles at molecular or ionic scale and remains stable, whereas a suspension contains larger dispersed particles that can settle on standing.
Why does milk show the Tyndall effect?
Milk contains colloidal particles that can scatter light.
Can filtration separate salt from salt water?
No. Dissolved salt particles pass through ordinary filter paper. Evaporation, crystallization or distillation may be selected depending on whether salt, solvent, or both need to be recovered.
Why is crystallization preferred in some cases?
Crystallization can produce comparatively pure solid crystals and may avoid problems associated with heating a solution to complete dryness.
Which method separates oil and water?
A separating funnel is suitable because oil and water are immiscible and form separate layers.
What determines the correct separation technique?
The choice depends on differences in physical properties such as particle size, solubility, density, volatility, boiling point and ability to sublime.
Related Study Path
After completing this chapter, students should revise the connected ideas of matter, particle behaviour, physical and chemical changes, motion of particles and laboratory separation techniques. Practice should include concept questions, numerical problems, comparison tables and labelled apparatus diagrams.
For stronger preparation, use MyMockMate chapter-wise solutions as a study aid alongside your prescribed textbook, class notes and teacher guidance.
