NCERT Curiosity · Class 8 · Science
The Amazing World of Solutes, Solvents, and Solutions
Every sip of homemade ORS tastes exactly the same, no matter how much you drink — a uniform mixture, from top to bottom.
Solutions Solubility Density Relative Density
Key idea
Solute, Solvent, and Solution

Solute

The substance that dissolves.

Solvent

The substance it dissolves in.

Solution

The uniform mixture that results.

Key idea
Saturated and Unsaturated Solutions
Unsaturated

Can still dissolve more solute at that temperature.

Saturated

No more solute can dissolve — any extra settles at the bottom.

Key idea
Concentration and Solubility
Concentration

The amount of solute in a fixed quantity of solution — dilute means less, concentrated means more.

Solubility

The maximum amount of solute that can dissolve at a given temperature.

Key idea
Solubility and Temperature
Solids: rises with heat

Heating water lets it dissolve more baking soda — true for most solid solutes.

Gases: falls with heat

Cold water holds more dissolved oxygen than warm water.

Key idea
Whether something floats or sinks is about density, not just weight.
A wooden stick and an iron rod of the same size differ hugely in “heaviness” — husk and oil float, rice and stone sink.
Key idea
Density = Mass ÷ Volume
A sample with mass 16.4 g and volume 5 cm³ has a density of 3.28 g/cm³. Density doesn't depend on shape or size.
Key idea
Measuring Mass and Volume
Regular solids

Mass from a balance; volume from length × width × height.

Irregular solids

Volume found by water displacement — the rise in a measuring cylinder.

Key idea
Relative density is just a ratio — no units needed.
Relative density = density of a substance ÷ density of water. Aluminium's relative density is about 2.7.
Key idea
Temperature, Pressure, and a Frozen Surprise
Hot air balloons

Hot air is less dense than the cool air around it, so it rises.

Ice floats

Freezing water spreads its particles apart, so ice is less dense and floats on water.

Chapter · key terms to remember
Key Terms

Solute / Solvent

What dissolves / what it dissolves in.

Solution

A uniform mixture of solute and solvent.

Saturated / Unsaturated

Can't / can still dissolve more solute.

Chapter · key terms to remember
More Key Terms

Concentration

Amount of solute in a fixed quantity of solution.

Solubility

Maximum solute dissolvable at a given temperature.

Density

Mass per unit volume (Mass ÷ Volume).

Chapter · key terms to remember
More Key Terms

Relative density

Ratio of a substance's density to water's.

Meniscus

The curved surface of a liquid in a container.

Opening

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