Solutions

Chromatography separates mixtures of dissolved substances based on how strongly they are attracted to a stationary material compared to how far they are carried by a moving solvent. It is used to identify unknown substances and test for purity.

Concentration tells us how much solute is dissolved in a given volume of solvent. Understanding concentration is essential in laboratory experiments, medicine, cooking, and industry — it affects the rate of reactions and the strength of solutions.

Crystallisation is a method of separating a dissolved solid from a solution by evaporating the solvent — usually water — until crystals grow. It is used to purify substances and produce high-quality crystals.

Distillation separates a liquid from a solution or separates two mixed liquids by heating the mixture so one liquid evaporates, then cooling the vapour so it condenses and is collected separately.

Evaporation is used to separate a dissolved solid (solute) from its solution by heating the solution so the solvent evaporates away. The solid solute is left behind as pure crystals.

Filtration is a separation technique used to separate an insoluble solid from a liquid (or gas) by passing the mixture through a filter. The liquid passes through while the solid is retained on the filter.

Master the three types of mass fraction calculation — finding the fraction, finding the solute mass, and finding the solution mass — with fully worked step-by-step examples.

Mass fraction tells you what proportion of a mixture is made up of one particular substance. Learn the formula, how it differs from concentration, and where you encounter mass fractions every day.

A mixture contains two or more substances that are not chemically combined. The substances keep their own properties and can be separated by physical methods such as filtering, evaporation, or distillation.

A pure substance contains only one type of substance with no other materials mixed in. Pure substances have sharp, fixed melting and boiling points, while impure substances (mixtures) melt and boil over a range of temperatures.

Solubility is the maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature. Temperature usually increases the solubility of solids, while it decreases the solubility of gases.

A solution is a homogeneous mixture formed when a solute dissolves in a solvent. Water is the most common solvent. The resulting solution looks clear and uniform throughout.

Not all mixtures are true solutions. Suspensions contain large insoluble particles that settle over time, while colloids have smaller particles that remain evenly dispersed. These mixtures are common in food, medicine, and everyday products.

Fresh water must be treated before it is safe to drink. This article explains how water is purified from natural sources to your tap, and why clean water is one of humanity's most important resources.