Solubility — States of Matter | IGCSE Chemistry | Examo

Solubility — States of Matter | IGCSE Chemistry | Examo

Exam Frequency Analysis

Past paper frequency (2018 to 2024)

This topic accounts for approximately 6% of your exam marks.

stable

Low

Stable6%

Appears regularly as short-answer questions on particle diagrams and state changes.

Solubility is how much solute a particular solvent will hold at a given temperature (and, for gases, at a given pressure)
Standard IGCSE unit: grams of solute per 100 g of solvent (usually water)
e.g. KNO₃ in water at 20 °C: 32 g per 100 g of water means 32 g dissolves; anything more sinks to the bottom

Effect of temperature and pressure

Solute	Effect of raising temperature	Effect of raising pressure
Solid	Usually more soluble	Negligible
Gas	Less soluble	More soluble

Warm fizzy drinks lose their fizz faster than cold ones (gas leaves on warming)
Carbonation is achieved by forcing CO₂ into solution under pressure

Solubility curves

A solubility curve plots solubility (g per 100 g of water) against temperature (°C)
Built by measuring the saturation mass at each of several temperatures and joining the points
Most ionic salts: curve rises with temperature
Shape varies sharply between salts:
- KNO₃: steep rise
- Pb(NO₃)₂: moderate rise
- NaCl: almost flat across 0–100 °C