ChemistryICSE Class 8 · Water

Solutions, Suspensions and Colloids; Saturated Solutions and Solubility (ICSE Class 8 Chemistry)

Q: Why is water called the universal solvent?

Because it dissolves a larger number of substances than any other liquid, though not everything (oil, wax and sand do not dissolve).

Q: What is solubility?

Solubility is the maximum mass of solute in grams that dissolves in 100 g of water at a given temperature to form a saturated solution.

Q: What is the Tyndall effect?

The scattering of a light beam by colloidal particles that makes the beam visible, as in a dusty room.

Updated 17 October 2026 · Fact-checked

A solute dissolves in a solvent to form a solution; water dissolves more substances than any other liquid, so it is the universal solvent. Solutions, colloids and suspensions differ in particle size. Solubility is the maximum mass of solute that dissolves in 100 g of water at a given temperature to give a saturated solution.

As particle size grows from solution to colloid to suspension, the mixture goes from clear, to scattering a light beam, to settling out.

Illustration drawn for QuestionBuddy.

Understand Solutions, Suspensions, Colloids and Solubility

Dissolution. The substance that dissolves is the solute, the liquid is the solvent, and the uniform mixture is the solution. Water particles attract the particles of a salt and pull them away from the crystal; they spread into the spaces between water particles. Dissolving is faster if you stir, heat or use powdered solute.

Universal solvent. Water dissolves more substances than any other liquid (salts, sugar, many acids and alkalis, gases such as oxygen and carbon dioxide). It does not dissolve oil, wax, sand or chalk.

Solutions, colloids and suspensions.

Property	Solution	Colloid	Suspension
Particle size	smallest (below about 1 nm)	between (1 to 100 nm)	largest (above about 100 nm)
Appearance	clear	translucent or cloudy	cloudy or opaque
Settles on standing?	no	no	yes
Passes through filter paper?	yes	yes	no
Tyndall effect?	no	yes	yes, or blocks the beam
Examples	salt or sugar in water	milk, ink, blood, starch in water, fog	chalk in water, muddy water

The Tyndall effect: a beam of light becomes visible in a colloid because its particles scatter the light.

Saturation.

Unsaturated: can dissolve more solute at that temperature.
Saturated: can dissolve no more; extra solute stays at the bottom.
Supersaturated: holds more solute than a saturated solution at that temperature (made by cooling a hot saturated solution carefully). It is unstable: shaking or a small crystal makes the extra solute crystallise at once.

Solubility at a given temperature $=$ the mass in grams of solute that dissolves in 100 g of water to make a saturated solution:

$solubility = \frac{mass of solute}{mass of water} \times 100$

For most solids, solubility increases with temperature; a hot saturated solution deposits crystals on cooling. Gases dissolve less in warm water.

Tests: add a little more solute. It dissolves: unsaturated. It does not: saturated. Crystals appear suddenly: supersaturated.

Solutions, Suspensions, Colloids and Solubility: formulas and key facts

Solubility: $solubility = \frac{mass of solute}{mass of water} \times 100$; g per 100 g of water at a stated temperature.
Solution: $solution = solute + solvent$; Masses add.
Crystals on cooling: $crystals = solubility_{hot} - solubility_{cold}$; Per 100 g of water.
Types of mixture: Solution no settling, no Tyndall effect
Colloid no settling, Tyndall effect
Suspension settles, filterable; By particle size.

Solution	no settling, no Tyndall effect
Colloid	no settling, Tyndall effect
Suspension	settles, filterable

How to solve Solutions, Suspensions, Colloids and Solubility questions

For solubility problems, scale everything to 100 g of water.

1Write the mass of solute and the mass of water in the saturated solution.
2Solubility $= \frac{solute}{water} \times 100$ .
3For another amount of water, scale proportionally.
4On cooling, crystals separate equal to the fall in solubility (per 100 g of water).
5Mass of solution $=$ solute $+$ water.

Solutions, Suspensions, Colloids and Solubility in real life

Each concept, met in an everyday situation. Read the situation, try the problem, then check the solution. The one-line hook is what to remember.

Tea sugar

Suppose 27 g of a salt just saturates 75 g of water at room temperature.

Find its solubility at that temperature.

Try it first, then show the solutionSolution

$solubility = \frac{27}{75} \times 100 = 36$ g per 100 g of water.

Answer: 36 g per 100 g of water.

Memory hook: Scale to 100 g of water.

Warm cold drink

Imagine a fizzy drink left in the Sun loses its fizz faster than one in the fridge.

Explain.

Try it first, then show the solutionSolution

Gases dissolve less in warm water.
Carbon dioxide escapes more easily when the drink is warm.

Answer: The solubility of the gas falls with temperature.

Memory hook: Warm drinks go flat.

Tricks to remember Solutions, Suspensions, Colloids and Solubility

Short memory aids. Say each one aloud once, then use it on a question the same day.

Small, middle, big
Solution (smallest), colloid (middle), suspension (largest).
Use it when: Particle size.
Tyndall shows a beam
Colloids make a light beam visible, like sunbeams in dusty rooms.
Use it when: Tyndall effect.
Per hundred
Solubility is always per 100 g of water.
Use it when: Numericals.

Solutions, Suspensions, Colloids and Solubility: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: A colloid · 1 mark · MCQBoard level

Which of the following scatters a beam of light but does not settle on standing?
(a) salt solution
(b) milk
(c) chalk in water
(d) sugar solution

Try it first, then show the solutionSolution

Milk is a colloid: it shows the Tyndall effect and does not settle.

Answer: (b) milk

Example 2: Solution versus suspension · 2 marks · Short answerBoard level

Give three differences between a true solution and a suspension.

Try it first, then show the solutionSolution

A solution is clear; a suspension is cloudy. (½)
A solution does not settle on standing; a suspension does. (½)
A solution passes through filter paper; a suspension does not. (1)

Answer: Clarity; settling; filtration.

Example 3: Solubility · 3 marks · Short answerHarder board level

18 g of a salt dissolves in 50 g of water to give a saturated solution at 30 °C. (a) Find its solubility at 30 °C. (b) How much salt is needed to saturate 200 g of water? (c) Find the mass of the saturated solution in (b).

Try it first, then show the solutionSolution

(a) $\frac{18}{50} \times 100 = 36$ g per 100 g. (1)
(b) $36 \times 2 = 72$ g. (1)
(c) $200 + 72 = 272$ g. (1)

Answer: (a) 36 (b) 72 g (c) 272 g

Example 4: Cooling · 4 marks · Long answerHarder board level

The solubility of a salt Y is 40 g per 100 g of water at 60 °C and 24 g per 100 g at 20 °C. A saturated solution containing 100 g of water at 60 °C is cooled to 20 °C. (a) How much Y is dissolved at 60 °C? (b) What mass of crystals separate? (c) What is the total mass of the solution at 20 °C?

Try it first, then show the solutionSolution

(a) 40 g. (1)
(b) $40 - 24 = 16$ g. (1½)
(c) $100 + 24 = 124$ g. (1½)

Answer: (a) 40 g (b) 16 g (c) 124 g

Example 5: Classify the mixtures · 4 marks · Case-basedHOTS / competency

A student tests four liquids: P (clear, no beam visible, passes filter paper), Q (cloudy, beam visible, passes filter paper), R (cloudy, settles, does not pass), S (clear, crystals appear suddenly when a seed crystal is added). (a) Classify P, Q and R. (b) What kind of solution is S? (c) Give an example for each of P, Q and R.

Try it first, then show the solutionSolution

(a) P: true solution; Q: colloid; R: suspension. (1½)
(b) Supersaturated solution. (1)
(c) P: salt in water; Q: milk; R: chalk in water. (1½)

Answer: (a) solution, colloid, suspension (b) supersaturated (c) as above

Where students lose marks in Solutions, Suspensions, Colloids and Solubility

The slips examiners see most often, and what to write instead.

Mistake: Solubility per any water
It is always per 100 g of water.
Wrong working
"18 g in 50 g water: solubility 18."
Right working
"Solubility = 36 g per 100 g."
Do this: Scale to 100 g.
Mistake: Thinking colloids settle
Colloids do not settle.
Wrong working
"Milk is a suspension."
Right working
"Milk is a colloid."
Do this: Use the settling test.
Mistake: Forgetting that gas solubility falls
Gases dissolve less in warm water.
Wrong working
"Gases dissolve more when hot."
Right working
"Gases dissolve less in warm water."
Do this: Contrast solids and gases.

Exam tips

Draw the three-column table in answers.
State solubility as "g per 100 g of water at … °C".
Mention the Tyndall effect for colloids.
Give two examples for each type.

Practice questions on Solutions, Suspensions, Colloids and Solubility

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · Very short answerBoard level
Name a colloid and a suspension from everyday life.
Hint
Milk, chalk.
Answer
Colloid: milk (or ink, blood). Suspension: muddy water (or chalk in water).
Q2 · 2 marks · Short answerHarder board level
27 g of a salt saturates 75 g of water at a certain temperature. Find the solubility.
Hint
Per 100 g.
Answer
$\frac{27}{75} \times 100 = 36$ g per 100 g of water.
Q3 · 3 marks · Short answerHarder board level
How would you test whether a given solution is unsaturated, saturated or supersaturated?
Hint
Add a little solute.
Answer
Add a small amount of solute. If it dissolves, the solution is unsaturated; if it does not, it is saturated; if crystals suddenly form around it, it is supersaturated.
Q4 · 2 marks · Short answerHarder board level
Why do fish find it harder to breathe in warm water? Explain with solubility.
Hint
Oxygen is a dissolved gas.
Answer
The solubility of gases such as oxygen decreases as water becomes warmer, so warm water holds less dissolved oxygen.
Q5 · 4 marks · Long answerHOTS / competency
A beam of light is passed through three glasses: salt solution, milk and muddy water. Describe what is seen in each, and what is learnt about particle size.
Hint
Tyndall effect.
Answer
Salt solution: the beam is not visible (very small particles). Milk: the beam is visible and the milk does not settle (colloid, medium particles). Muddy water: the beam is visible or blocked and mud settles on standing (suspension, large particles). The order of particle size is solution < colloid < suspension.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Particle size order?Show answer
Solution < colloid < suspension.
2.Tyndall effect shown by?Show answer
Colloids (and suspensions).
3.Solubility is measured per?Show answer
100 g of water.
4.A supersaturated solution is?Show answer
Unstable; crystallises on disturbance.
5.Gas solubility with temperature?Show answer
Decreases.

Solutions, Suspensions, Colloids and Solubility: frequently asked questions

Why is water called the universal solvent?

Because it dissolves a larger number of substances than any other liquid, though not everything (oil, wax and sand do not dissolve).

What is solubility?

Solubility is the maximum mass of solute in grams that dissolves in 100 g of water at a given temperature to form a saturated solution.

What is the Tyndall effect?

The scattering of a light beam by colloidal particles that makes the beam visible, as in a dusty room.