Solutions

Lesson

Part 1 — how much solute is in a solution, how much can dissolve, and how a solution’s vapour behaves.

In this lesson you will

Express the concentration of a solution as mass percentage, ppm, mole fraction, molarity and molality, and convert between them
Explain the factors that affect the solubility of solids and gases and apply Henry’s law
Apply Raoult’s law to mixtures of volatile liquids and to solutions of non-volatile solutes
Distinguish ideal and non-ideal solutions, explain positive and negative deviations and describe azeotropes

Concept

Types of solutions

The component present in the larger amount is the solvent; the others are solutes. The solvent decides the physical state, so there are nine combinations. Most of this chapter is about liquid solutions.

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 (water vapour in air)
Gas	Solid	Naphthalene vapour in a wardrobe’s air
Liquid	Gas	Soda water (carbon dioxide in water)
Liquid	Liquid	Ethanol in water
Liquid	Solid	Sugar syrup
Solid	Gas	Hydrogen absorbed in palladium
Solid	Liquid	Amalgam of mercury with sodium
Solid	Solid	Brass (zinc in copper)

Concept

Concentration by mass and by volume

Concentration tells us how much solute is present in a given amount of solution or solvent. Percentages and parts per million suit everyday and very dilute solutions.

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

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