The Amazing World of Solutes, Solvents and Solutions — Class 8 MCQs with Answers

The Amazing World of Solutes, Solvents and Solutions — important questions & MCQs with answers (Class 8 Science)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   The substance that dissolves in a liquid is the:

   AsolventBsoluteCsolutionDmixture
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   Answer: solute

   Explanation: The substance that dissolves is called the solute — sugar in tea, salt in water. The liquid doing the dissolving plays a different role, the solvent.

2. Q2 of 6Easy

   A solution in which more solute can still dissolve at a given temperature is:

   AsaturatedBonly diluteCunsaturatedDonly concentrated
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   Answer: unsaturated

   Explanation: An unsaturated solution can still take up more solute at that temperature, unlike a saturated one which has reached its limit.

3. Q3 of 6Medium

   Which of these is a solution?

   Asugar dissolved in waterBsand in waterCoil in waterDchalk powder in water
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   Answer: sugar dissolved in water

   Explanation: Sugar dissolved in water forms a true solution because it disperses evenly at the molecular level; sand, oil and chalk powder stay visibly separate instead.

4. Q4 of 6Medium

   A block has a mass of 20 g and a volume of 10 cm³. Its density is:

   A200 g/cm³B2 g/cm³C0.5 g/cm³D30 g/cm³
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   Answer: 2 g/cm³

   Explanation: Density = mass ÷ volume = 20 g ÷ 10 cm³ = 2 g/cm³.

5. Q5 of 6Hard

   The best one-line summary of this chapter is:

   Ait is only about saltBit studies how substances dissolve, and why things float or sink (density)Cit is only about gasesDmatter has no properties
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   Answer: it studies how substances dissolve, and why things float or sink (density)

   Explanation: This chapter covers two connected ideas: how solutes dissolve in solvents to form solutions of varying concentration, and how density explains why objects float or sink.

6. Q6 of 6Hard

   To dissolve the most sugar in water, you should use water that is:

   AhotBice-coldCfrozenDboiling then frozen
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   Answer: hot

   Explanation: Hot water has higher solubility for sugar than cold water, so heating the water before adding sugar lets the most dissolve.

The Amazing World of Solutes, Solvents and Solutions notes: key concepts (Class 8 Science)

This chapter explores how substances dissolve and why things float or sink. When a solute dissolves in a solvent it forms a solution — a uniform mixture. Solubility is the maximum solute that dissolves in a fixed amount of solvent at a given temperature, and a solution is saturated when no more will dissolve. The solubility of most solids rises with temperature, while gases dissolve less as water warms, which matters for the dissolved oxygen that keeps aquatic life alive. The chapter also defines density (Density = Mass ÷ Volume) and uses it to explain that objects less dense than a liquid float, while denser ones sink.

Solute, solvent, solution

The solute is the substance that dissolves, the solvent is the liquid it dissolves in (present in the larger amount), and together they make a solution.

Solubility

The maximum amount of a solute that dissolves in a fixed quantity of solvent at a given temperature.

Saturated and unsaturated

A saturated solution can dissolve no more solute at that temperature; an unsaturated one can still dissolve more.

Concentration

How much solute is present in a solution; a dilute solution has little solute and a concentrated solution has a lot.

Temperature and solids

The solubility of most solids increases as the temperature rises, so a saturated solution can dissolve more when heated and may crystallise when cooled.

Solubility of gases

Gases dissolve in water only a little and their solubility decreases as temperature rises, so cold water holds more dissolved oxygen for aquatic life than warm water.

Uniform and non-uniform mixtures

A uniform (homogeneous) mixture is a solution whose components are not visible separately; in a non-uniform mixture, like sand in water, the parts can be seen.

Density

The mass present in a unit volume of a substance, Density = Mass ÷ Volume; it depends on the material, not on the shape or size, and its SI unit is kg/m³ (water is about 1 g/cm³).

Relative density

The density of a substance compared with the density of water — its density divided by that of water.

Floating and sinking

An object floats in a liquid if it is less dense than the liquid and sinks if it is denser, which is why oil floats on water and a stone sinks.

Density and temperature

Heating usually expands a substance and lowers its density; water is unusual in having its greatest density at 4 °C.