ScienceCBSE Class 8 · The Amazing World of Solutes, Solvents, and Solutions

Solutes, Solvents, Solubility and Saturated Solutions: Class 8 Science

Updated 17 October 2026 · Fact-checked

A solution is a uniform mixture of two or more substances. When a solid dissolves in a liquid, the solid is the solute and the liquid is the solvent. A solution that can dissolve more solute at a given temperature is unsaturated; when no more dissolves it is saturated. Solubility is the maximum amount of solute dissolved in a fixed quantity of solvent at a temperature; for most solids it rises with temperature, but for gases it falls.

Once water cannot dissolve more salt, the extra settles at the bottom; heating usually lets a solid dissolve more.

Illustration drawn for QuestionBuddy.

Understand Solutes, Solvents, Solubility and Saturated Solutions

Solution. A homemade ORS tastes the same in every sip because salt and sugar spread evenly through the water: a uniform mixture, which is called a solution. Chalk powder, sand or sawdust in water make non-uniform mixtures because the components are not evenly distributed. In a solution of a solid in a liquid, the solute is the solid and the solvent is the liquid. When two liquids are mixed, the one in smaller amount is called the solute and the other the solvent. Even in gulab jamun chashni, with a lot of sugar and a little water, water is the solvent and sugar the solute. A mixture of gases such as air is also a uniform mixture.

Saturated and unsaturated solutions (Activity 9.1). Add salt spoon by spoon to half a tumbler of water and stir. Initially it dissolves completely; after a few spoons the added salt settles at the bottom, since water has reached its limit. A solution in which more solute can still be dissolved at a given temperature is unsaturated. A solution in which no more solute can dissolve at that temperature, so that extra solute settles, is saturated.

Concentration. The amount of solute present in a fixed quantity of solution or solvent is its concentration. A solution with less solute is dilute and one with more solute is concentrated; these are relative terms. For example, 4 spoons of salt in 50 mL of water is more concentrated than 2 spoons in 100 mL.

Solubility. The maximum amount of solute that dissolves in a fixed quantity (the chapter's summary uses 100 mL) of solvent at a particular temperature is its solubility.

Temperature and solid solutes (Activity 9.2, demonstration). In about 50 mL of water at 20 degrees Celsius baking soda is added until some remains undissolved. On heating to 50 degrees Celsius the undissolved soda dissolves; more is added until some again remains; at 70 degrees Celsius that also dissolves. So water at 70 degrees Celsius dissolves more baking soda than at 50 degrees Celsius, and at 20 degrees Celsius even less. For most substances the solubility increases with temperature. A saturated solution at one temperature behaves like an unsaturated solution if the temperature is raised.

Gases in liquids. Many gases, including oxygen, dissolve in water only to a small extent, forming a uniform mixture. This dissolved oxygen sustains aquatic life. The solubility of gases generally decreases as the temperature rises, so cold water holds more oxygen; warming reduces dissolved oxygen.

Heritage and people. In Ayurveda, Siddha and other traditional systems water, hydro-alcoholic extracts, oils, ghee and milk are used as solvents for drug formulations. Asima Chatterjee used solvents and solutions to extract compounds from medicinal plants; she was the first woman to receive the Shanti Swarup Bhatnagar Award in chemical science.

The next topic deals with mass, volume and density.

Solutes, Solvents, Solubility and Saturated Solutions: formulas and key facts

Solution: Solute + Solvent > Solution (uniform mixture); Solid in liquid: solid is solute. Liquid in liquid: smaller amount is solute.
Saturated and unsaturated: Unsaturated: more solute can dissolve | Saturated: no more solute dissolves at that temperature; Undissolved solute settles at the bottom.
Concentration: $A m o u n t o f so l u t e ina f i x e d q u an t i t y o f so l u t i o n ∣ D i l u t e = l ess ∣ C o n ce n t r a t e d = m or e$; Relative terms.
Solubility: Maximum solute dissolved in a fixed quantity of solvent at a given temperature; Chapter's summary: per 100 mL.
Effect of temperature: Solids in liquids: solubility increases with temperature | Gases in liquids: solubility decreases with temperature; For most substances.

How to solve Solutes, Solvents, Solubility and Saturated Solutions questions

Use this method for solution questions.

1Identify the solute and the solvent: solid in liquid, solid is solute; two liquids, smaller amount is solute.
2Decide if the mixture is uniform. If yes, it is a solution.
3To compare concentrations, compare solute per fixed volume (convert to the same volume).
4For saturation, look for undissolved solute at the stated temperature.
5For temperature effects, say solids dissolve more on heating and gases less.
6State the conclusion with the right term: dilute, concentrated, saturated or unsaturated.

Solutes, Solvents, Solubility and Saturated Solutions 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.

Comparing concentrations

Suppose tumbler P has 2 spoons of salt in 100 mL of water and tumbler Q has 4 spoons of salt in 50 mL of water (the chapter's pair, with the same size of spoons assumed).

(a) Find the spoons of salt per 100 mL in each tumbler. (b) Which is more concentrated and how many times? (c) If the water in P is evaporated to 50 mL, what happens to its concentration? (d) Is Q necessarily saturated?

Try it first, then show the solutionSolution

P: 2 spoons per 100 mL. Q: 4 spoons in 50 mL = 8 spoons per 100 mL.
Q is more concentrated: 8 ÷ 2 = 4 times.
P would then have 2 spoons in 50 mL = 4 spoons per 100 mL, so its concentration doubles.
Not necessarily; it is saturated only if no more salt can dissolve at that temperature.

Answer: (a) 2 and 8 spoons per 100 mL; (b) Q, 4 times; (c) doubles; (d) not necessarily.

Memory hook: Concentration is solute per fixed amount, not just total solute.

Fish in warm water

Imagine a pond in summer where the water warms and fish come to the surface and gasp, while in winter they are comfortable.

(a) How does the solubility of oxygen change with temperature? (b) Why do fish struggle in warm water? (c) Which water holds more oxygen: at 10 or at 30 degrees Celsius?

Try it first, then show the solutionSolution

The solubility of gases generally decreases as temperature increases.
Warm water holds less dissolved oxygen, which is needed by aquatic life.
The water at 10 degrees Celsius is colder and holds more oxygen.

Answer: (a) It decreases with temperature; (b) less dissolved oxygen; (c) 10 degrees Celsius.

Memory hook: Cold keeps the gas, heat lets it go.

Tricks to remember Solutes, Solvents, Solubility and Saturated Solutions

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

Solid solute, Liquid solvent
Solute is the Solid (S with S). Solvent is the liquid that holds it.
Use it when: Identifying the parts.
Sat = sit
Saturated solution: extra solute sits at the bottom.
Use it when: Recognising saturation.
Solids like hot, gases like cold
Solids dissolve better when hot; gases dissolve better when cold.
Use it when: Effect of temperature.

Solutes, Solvents, Solubility and Saturated Solutions: solved examples

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

Example 1: Identify solute and solvent · 3 marks · Short answerBoard level

Name the solute and the solvent in: (a) salt in water, (b) a mixture of 10 mL of acetic acid and 90 mL of water, (c) gulab jamun chashni.

Try it first, then show the solutionSolution

(a) Salt is the solute; water is the solvent. (1)
(b) Acetic acid (smaller amount) is the solute; water is the solvent. (1)
(c) Sugar is the solute; water is the solvent, though sugar is present in large amount. (1)

Answer: (a) Salt, water; (b) acetic acid, water; (c) sugar, water.

Example 2: Saturated solution · 1 mark · MCQBoard level

A solution in which no more solute can dissolve at a given temperature is called
(a) dilute
(b) concentrated
(c) saturated
(d) unsaturated

Try it first, then show the solutionSolution

The limit of dissolving has been reached: saturated.

Answer: (c)

Example 3: Heating a saturated solution · 5 marks · Long answerHarder board level

Baking soda is added to 50 mL of water at 20 degrees Celsius until some stays undissolved. The beaker is then heated to 50 degrees Celsius and then 70 degrees Celsius.
(a) What happens to the undissolved soda at 50 degrees Celsius? (1)
(b) What type of solution was it at 20 degrees Celsius, and at 50 degrees Celsius just after the soda dissolved? (2)
(c) How does the solubility compare at 20, 50 and 70 degrees Celsius? (1)
(d) Predict what happens when the 70 degree solution cools to 20 degrees Celsius. (1)

Try it first, then show the solutionSolution

(a) It dissolves. (1)
(b) At 20 degrees Celsius it was saturated. At 50 degrees Celsius, just after dissolving, it behaves as unsaturated (more can be added). (2)
(c) Solubility is least at 20, more at 50 and most at 70 degrees Celsius. (1)
(d) Solubility decreases, so some soda comes out as solid again (a prediction from the trend; the chapter shows only the heating direction). (1)

Answer: (a) Dissolves; (b) saturated then unsaturated; (c) 20 < 50 < 70; (d) some solid separates on cooling.

Example 4: Dissolved oxygen · 4 marks · Case-basedHarder board level

Read the passage and answer.

A pond has more dissolved oxygen in winter than in summer. A student says that gases behave like sugar: more of them dissolve when the water is hot.
(a) State the effect of temperature on solubility of gases. (1)
(b) Evaluate the student's claim. (1)
(c) Why does dissolved oxygen matter? (1)
(d) Is oxygen in water a uniform or non-uniform mixture? (1)

Try it first, then show the solutionSolution

(a) It generally decreases as temperature increases. (1)
(b) Wrong: for gases solubility falls with heating; for most solids it rises. (1)
(c) It sustains all aquatic life, including plants and fish. (1)
(d) Uniform. (1)

Answer: (a) Decreases; (b) incorrect; (c) aquatic life needs it; (d) uniform.

Example 5: Which statement is correct · 4 marks · Case-basedHOTS / competency

Read the passage and answer.

Four students describe a saturated solution: (i) It can still dissolve more solute at the same temperature. (ii) It has dissolved the maximum solute possible at that temperature. (iii) It forms only at high temperatures. (iv) Heating it can make it behave as unsaturated.
(a) Which two statements are correct? (1)
(b) Explain why (i) is wrong. (1)
(c) Explain why (iii) is wrong. (1)
(d) A tumbler holds 100 mL of water and 36 spoons of salt, of which 4 are undissolved. How many spoons are in solution? (1)

Try it first, then show the solutionSolution

(a) (ii) and (iv). (1)
(b) A saturated solution cannot dissolve more solute at that temperature. (1)
(c) A solution can be saturated at any temperature; its solubility value differs with temperature. (1)
(d) 36 − 4 = 32 spoons (the same size of spoons assumed), and the solution is saturated. (1)

Answer: (a) (ii) and (iv); (b) no more can dissolve; (c) saturation occurs at any temperature; (d) 32 spoons.

Where students lose marks in Solutes, Solvents, Solubility and Saturated Solutions

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

Mistake: Naming sugar as the solvent in chashni.
There is more sugar than water.
Wrong working
Sugar is the solvent because it is present in larger amount.
Right working
Water is the solvent and sugar the solute even though sugar is more in amount.
Do this: Solid in liquid: solid is the solute.
Usually costs: 1 mark.
Mistake: Saying a saturated solution is the same as a concentrated solution.
Both have a lot of solute.
Wrong working
Concentrated and saturated are the same.
Right working
Concentrated is relative; saturated means no more solute dissolves at that temperature.
Do this: Check for undissolved solute.
Usually costs: 1 mark.
Mistake: Applying the temperature rule of solids to gases.
One rule is recalled.
Wrong working
Oxygen dissolves more in hot water.
Right working
The solubility of gases decreases with increase in temperature.
Do this: Solids like hot, gases like cold.
Usually costs: 1 mark.
Mistake: Comparing concentration without equalising the volume.
Totals are compared directly.
Wrong working
4 spoons > 2 spoons so the first is more concentrated, whatever the volume.
Right working
Compare spoons per 100 mL: 4 in 50 mL is 8 per 100 mL, against 2 per 100 mL.
Do this: Divide by volume.
Usually costs: 1 to 2 marks.

Exam tips

Define each term with the temperature condition where the chapter does.
Say 'at a particular temperature' in saturated and solubility definitions.
Compare concentrations by solute per fixed volume.
State separately the temperature effect on solids and gases.
In prediction questions, mark your answer as a prediction if the chapter does not state it.

Practice questions on Solutes, Solvents, Solubility and Saturated Solutions

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

Q1 · 2 marks · Very short answerBoard level
Define solubility. What is the general effect of temperature on the solubility of a solid in a liquid?
Hint
Maximum amount in a fixed quantity.
Answer
Solubility is the maximum amount of solute that dissolves in a fixed quantity of the solvent at a given temperature (1). For most solids it increases with temperature (1).
Q2 · 1 mark · MCQBoard level
Which of the following is a solution?
(a) Sand and water
(b) Sawdust and water
(c) Salt in water
(d) Chalk powder in water
Hint
Uniform mixture.
Answer
(c)
Q3 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Fish find it harder to breathe in a warm pond than in a cool one.
Reason (R): The solubility of oxygen in water decreases as the temperature rises.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true 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.
Hint
Less dissolved oxygen.
Answer
(a) R explains A.
Q4 · 4 marks · Short answerHarder board level
A student dissolves salt in 200 mL of water at room temperature and finds that 72 g dissolves before the rest stays at the bottom. (a) Find the solubility of salt in g per 100 mL at that temperature. (b) How much would dissolve in 350 mL at the same temperature? (c) If the student adds 100 g in 200 mL, how much stays undissolved? (d) What type of solution is it after that?
Hint
Scale by volume.
Answer
(a) 72 ÷ 2 = 36 g per 100 mL. (b) 36 × 3.5 = 126 g. (c) 100 − 72 = 28 g. (d) Saturated (1 mark each).
Q5 · 4 marks · Case-basedHOTS / competency
Read the passage and answer.
A student prepares two solutions: X has 5 g of sugar in 100 mL of water and Y has 12 g of sugar in 150 mL of water at the same temperature. Both are clear.
(a) Find the sugar per 100 mL in each. (b) Which is more concentrated? (c) Can we say whether either is saturated? (d) What simple test will show if X is saturated?
Hint
12 g in 150 mL = 8 g in 100 mL.
Answer
(a) X: 5 g per 100 mL; Y: 12 ÷ 1.5 = 8 g per 100 mL. (b) Y. (c) No; both are clear, so we cannot tell without testing whether more sugar dissolves. (d) Add a little more sugar and stir: if it stays undissolved, X was saturated (1 mark each).

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.What is a solution?Show answer
A uniform mixture of two or more substances.
2.In a solid-in-liquid solution, which is the solute?Show answer
The solid.
3.What is an unsaturated solution?Show answer
One in which more solute can still dissolve at that temperature.
4.Which gas dissolved in water sustains aquatic life?Show answer
Oxygen.
5.What happens to the solubility of gases as temperature rises?Show answer
It generally decreases.

Solutes, Solvents, Solubility and Saturated Solutions: frequently asked questions

Why do sugar and salt dissolve in water but not in oil?

This is a question posed in the chapter's opening page; the chapter itself does not answer it. You will study it in later classes.

Is every transparent liquid a solution?

A solution is a uniform mixture. Clear appearance alone does not tell whether it is saturated or unsaturated.

Why does sand in water not form a solution?

The components are not evenly distributed, so it is a non-uniform mixture.

How is a saturated solution made to dissolve more solute?

By raising the temperature, since for most solids solubility increases with temperature.