Solution — Chemistry Definition, Types & Examples

Written by

Malcolm McKinsey

January 12, 2023

Fact-checked by

Paul Mazzola

What is a solution?

A solution in science is a homogenous mixture of two or more substances. Solutions appear to be one substance, but the parts of a solution are not chemically bonded. Solutions can exist in any phase of matter, and the proportions of substances in a solution can vary up to the limit of solubility.

Parts of a solution

A solution is made up of a solvent and a solute. The larger amount in a solution is called the solvent, and substances in lesser amounts are solutes.

Types of solutions

Solutions can be any combination of solids, liquids, and gases. All solutions are described or characterized by the state of matter of their solvent, not their solutes.

Since we typically deal with three different phases of matter at normal conditions (solids, liquids, and gases), we can have six combinations of these states of matter in forming solutions:

1. Solid/Solid

2. Solid/Liquid

3. Solid/Gas

4. Liquid/Liquid

5. Liquid/Gas

6. Gas/Gas

A hallmark characteristic of a solution is that any sample will be virtually identical to any other sample because the substances are so thoroughly mixed.

For example, sampling a water and isopropyl alcohol solution will always give the same proportions of the two substances.

Properties of solutions

All solutions have these properties:

• A solution is a homogeneous mixture.

• Solutions are mixtures of a solvent and various solutes.

• Solute particles cannot be separated by filtration.

• Solutions are stable at a given temperature.

• Solutions can be saturated, unsaturated, or supersaturated.

To form a solution, solutes dissolve into solvents until the solvent can accept no more solute under normal conditions. The amount of solute that the solvent can handle is called the limit of solubility.

It is possible to have a solution where the solvent and solute exist in equal amounts, such as a solution of 50% ethanol and 50% water. In this case, the solvent is often determined to be the compound that is most commonly used as the solvent in other solutions. In this example, you would refer to water as the solvent.

A saturated solution is a solution where the solvent has reached its limit of solubility. When the solvent cannot dissolve all of the solute, you might find bits of solute at the bottom of the container.

A solution at less than the limit of solubility is unsaturated. Any solute to a solvent that has reached its saturation point or limit of solubility creates a supersaturated solution.

Because the exact proportions of solute and solvent can vary in a solution, no solution can be written as a chemical formula. This, in addition to the lack of chemical bonding, differentiates solutions from compounds.

Solutions can be separated into their solutes and solvents, which can be very difficult, time-consuming, or expensive to do.

On the other hand, merely opening a bottle of carbonated beverage like soda will separate the carbon dioxide gas, a solute, from the sugar water, the solvent. The bubbles of gas escaping the solution give the soda its welcome fizz.

Solution examples

Examples of solutions include air, sugar water, steel, saltwater, pancake syrup, and natural gas.

Air is an example of a gaseous solution (gas/gas). The air we breathe exists in roughly these proportions, and because it is a solution, every sample will nearly match every other sample:

• 78% nitrogen ($N$)

• 21% oxygen ($O$)

• 0.93% argon ($Ar$)

• 0.4% carbon dioxide ($C{O}_{2}$)

• Additional trace amounts of neon ($Ne$), helium ($He$), methane ($C{H}_{4}$), krypton ($Kr$), hydrogen ($H$), and water molecules (${H}_{2}O$)

Another example of a gaseous solution is natural gas, a homogeneous mixture of methane ($C{H}_{4}$) as the solvent and butane (${C}_{4}{H}_{10}$), ethane (${C}_{2}{H}_{6}$), and propane (${C}_{3}{H}_{8}$) as the solutes.

Solid/solid solutions include steel, bronze, brass, jeweler’s gold, and pewter. Solid solutions are called alloys.

Nearly every piece of metal you see daily is an alloy, with the notable exception of elemental iron, $Fe$. Still, even iron often contains additives to make it more workable and less brittle than it is by itself.

Gas/liquid solutions provide comfortable homes for fish indoors and out, with fish ponds and aquariums forcing gaseous oxygen into the liquid water, along with other solutes to keep the fish’s water clean.

Solid/liquid solutions include toothpaste (with abrasive solids as the solutes), saltwater (water and sodium chloride, $NaCl$), sugar water, and sweetened tea or coffee.

Solid/gas solutions are rare, but camphor in hydrogen gas is one example.

Common solutions in the home

Examples of liquid/liquid solutions are probably in your kitchen:

• Household liquid cleaners, almost all of which use pure water as the liquid solvent with various solutes dissolved into it

• Liquid soap, which is mostly pure water with solutes of surfactants and detergents

• Disinfectants, which use pure water as the solvent for various germ-killing chemicals

• Vinegar, a mixture of 97% pure water (the solvent) and 3% acetic acid (the solute)

Your bathroom may have liquid/liquid solutions, too:

• Hydrogen peroxide, ${H}_{2}{O}_{2}$

• Mouthwash

Frequently asked questions about solutions

Review what you know by answering these questions.

1. What are the parts of a solution?

2. Are solutions homogeneous or heterogeneous mixtures?

3. Is air a solution?

4. Is oxygen a solution?

See how you did by checking your work against our answers below.

1. Solvents and solutes are the two parts of a solution.

2. Solutions are homogeneous mixtures, so they appear to be one substance to the naked eye.

3. Yes, the air we breathe is a solution made up of elements on the periodic table, such as nitrogen, oxygen, and Argon.

4. No, oxygen is just one chemical substance. Oxygen is not a solution.