The Amazing World of Solutes Solvents and Solutions
When sugar disappears into tea, it forms a solution. This Class 8 Curiosity chapter explains solutes, solvents and solutions, the difference between dilute, concentrated and saturated solutions, how solubility changes with temperature, and how true solutions differ from suspensions and colloids.
Learning objectives
- Define solute, solvent and solution.
- Distinguish dilute, concentrated, saturated and unsaturated solutions.
- Explain solubility and how temperature affects it.
- Compare solutions, suspensions and colloids.
Key concepts
Solute, solvent and solution
A solution is a homogeneous mixture of two or more substances. The substance that dissolves is the solute (sugar), and the one in which it dissolves is the solvent (water). When water is the solvent, the solution is called aqueous. In a true solution the solute particles are so tiny that they spread evenly and do not settle.
Dilute, concentrated and saturated solutions
A dilute solution has a small amount of solute, while a concentrated solution has a large amount. At a given temperature, a solution that can still dissolve more solute is unsaturated; once it can dissolve no more, it is saturated. Any extra solute added to a saturated solution simply settles at the bottom.
Solubility and temperature
Solubility is the maximum amount of a solute that dissolves in a fixed amount of solvent at a given temperature. For most solids, solubility increases as temperature rises, which is why more sugar dissolves in hot water than in cold. Concentration tells how much solute is present and can be written as a percentage by mass.
Solutions, suspensions and colloids
In a suspension, like chalk in water, the particles are large, visible, and settle on standing; a suspension is heterogeneous. A colloid, like milk, has medium-sized particles that do not settle but scatter a beam of light (the Tyndall effect). A true solution is clear, does not settle, and does not scatter light.
Important formulas
Concentration (% by mass)
= (mass of solute ÷ mass of solution) × 100
Key definitions
- Solute
- The substance that dissolves in a solvent to form a solution.
- Solvent
- The substance in which a solute dissolves, present in larger amount.
- Saturated solution
- A solution that can dissolve no more solute at a given temperature.
- Solubility
- The maximum mass of solute that dissolves in a fixed mass of solvent at a given temperature.
Solved examples
Q1. In salt water, name the solute and the solvent.
Solution: Salt is the solute and water is the solvent.
Q2. 20 g of sugar is dissolved to make 100 g of solution. Find the concentration by mass.
Solution: Concentration = (20 ÷ 100) × 100 = 20% by mass.
Q3. Why does more sugar dissolve in hot tea than in cold water?
Solution: Solubility of most solids increases with temperature, so hot water dissolves more sugar.
Common mistakes to avoid
- Thinking the solute is destroyed — it is still present, just evenly spread.
- Confusing 'concentrated' with 'saturated' — a concentrated solution may still dissolve more.
- Believing all mixtures of solid and liquid are solutions (chalk in water is a suspension).
- Forgetting that the denominator in % by mass is the mass of the whole solution, not just the solvent.
The Amazing World of Solutes Solvents and Solutions — MCQ Quiz
10 questions with instant feedback. Use number keys 1–4 to answer.
In a sugar solution, the solvent is:
Practice questions
Short answer
Define a solution.
A homogeneous mixture of a solute dissolved in a solvent.
What is solubility?
The maximum amount of a solute that dissolves in a fixed amount of solvent at a given temperature.
How does a colloid differ from a true solution?
A colloid has larger particles that scatter light (Tyndall effect) but do not settle, while a true solution is clear and does not scatter light.
Long answer
Explain dilute, concentrated, unsaturated and saturated solutions.
A dilute solution contains only a little solute, and a concentrated solution contains a large amount, so these terms compare how much solute is dissolved. At a fixed temperature, an unsaturated solution can still dissolve more solute, while a saturated solution has dissolved the maximum it can hold; any extra solute then settles. Heating a saturated solution can let it dissolve still more, since solubility usually rises with temperature.
Compare true solutions, colloids and suspensions.
A true solution (salt in water) has very tiny particles, is clear, does not settle, and does not scatter light. A colloid (milk) has medium-sized particles that stay dispersed, do not settle, and scatter a light beam, showing the Tyndall effect. A suspension (chalk in water) has large, visible particles that settle on standing and is heterogeneous. So particle size increases from solution to colloid to suspension.
HOTS (Higher Order Thinking)
A beam of light passes invisibly through salt water but is visible in milk. Explain.
Salt water is a true solution with particles too small to scatter light, so the beam is invisible; milk is a colloid whose larger particles scatter the light (Tyndall effect), making the beam visible.
On a hot day, a saturated sugar solution is cooled. What may you observe and why?
Sugar crystals may appear, because solubility falls as temperature drops, so the cooled solution can no longer hold all the dissolved sugar and the excess separates out.
Quick revision
Revision notes
- Solution = solute + solvent (homogeneous); water solvent → aqueous.
- Dilute vs concentrated (amount); unsaturated vs saturated (capacity at that temperature).
- Solubility usually rises with temperature; concentration can be % by mass.
- Solution < colloid < suspension in particle size; colloids show Tyndall effect.
Key takeaways
- A saturated solution holds the maximum solute at that temperature.
- Temperature strongly affects how much solid dissolves.
- Particle size separates solutions, colloids and suspensions.
Frequently asked questions
What is the difference between a solute and a solvent?
The solute is the substance that dissolves; the solvent is the substance it dissolves in.
What is a saturated solution?
One that has dissolved the maximum amount of solute possible at a given temperature.
How can you tell a colloid from a solution?
A colloid scatters a beam of light (Tyndall effect); a true solution does not.