Solutions

Secondary 3

A solution is a homogeneous mixture composed of a solvent and one or more solutes.

An aqueous solution is a solution in which the solvent is water.

Solutions are usually liquids. In a solution, it is impossible to differentiate between the different components of the mixture. Solutions must have only one phase, whether macroscopically (seen with the naked eye) or microscopically (seen through a microscope).

When water and sugar are combined, the resulting sugar water is a solution because it is impossible to distinguish between the components (either with the naked eye or through a microscope).

However, milk is not a solution. While it is impossible to distinguish between the components with the naked eye, some of the different elements that make up milk can be observed under a microscope, as seen in the following image.

Solid solutions, or alloys, also exist. An alloy is a homogeneous mixture of several solids.

A bronze medal is a copper and tin alloy.

Solute

A solute is the substance that dissolves in a solvent.

In a sugar water solution, the sugar is the solute.

Solvent

A solvent is the substance found in the largest amount in a solution.

The solute is dissolved in the solvent.

In a sugar water solution, the water is the solvent.

Be careful!

There can be more than one solute in a solution, but only one substance can be the solvent.

Urine contains over 3 000 components. Water, which makes up 95% of urine, is the solvent, while all other components (urea, minerals, etc.) are solutes.

Plasma is also composed of mostly water (about 90%), which is the solvent. Plasma solutes include salts, lipids and hormones.

The following table shows different examples of solutions based on the different states of matter.

Solution Classification
Physical state of the solution Solute state Solvent state Examples
gas gas gas air (mixture of mainly nitrogen and oxygen gases)
- - -
- - -
liquid gas liquid oxygen in water
liquid liquid alcohol in water
solid liquid sugar in water
solid gas solid hydrogen in palladium
liquid solid mercury in gold
solid solid carbon in steel