Solutions and Their Concentration

Lesson

Part 1 — what a solution is, how strong it is, and how much gas a liquid can hold.

In this lesson you will

Classify solutions by the states of solute and solvent, including solid solutions
Calculate mass percentage, ppm, mole fraction, molarity, molality and normality, and convert between them
Explain why molality, unlike molarity, does not change with temperature
Apply Henry’s law and explain its everyday applications

Concept

Types of solutions

The component present in the larger amount is the solvent; the others are solutes. The solvent decides the physical state. Solid solutions include alloys such as brass and amalgams.

Table of the nine types of solution by the state of the solvent and the solute, with an example of each
Solvent	Solute	Example
Gas	Gas	Air (oxygen in nitrogen)
Gas	Liquid	Humid air
Gas	Solid	Camphor vapour in air
Liquid	Gas	Soda water (CO₂ in water)
Liquid	Liquid	Ethanol in water
Liquid	Solid	Salt solution
Solid	Gas	Hydrogen in palladium
Solid	Liquid	Sodium amalgam (mercury in sodium)
Solid	Solid	Brass, bronze, 22-carat gold

Concept

Percentages and parts per million

Percentages and parts per million suit labels and very dilute solutions.

Table of mass percentage, volume percentage, mass by volume percentage and parts per million with definitions and uses
Term	Definition	Typical use
Mass percentage (w/w)	$\dfrac{\text{mass of component}}{\text{mass of solution}} \times 100$	Commercial acids
Volume percentage (v/v)	$\dfrac{\text{volume of component}}{\text{volume of solution}} \times 100$	Sanitiser, antifreeze
Mass by volume (w/v)	grams of solute per 100 mL of solution	Saline, medicines
Parts per million (ppm)	$\dfrac{\text{mass of component}}{\text{mass of solution}} \times 10^{6}$	Fluoride in water, pollutants

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