Some substances dissolve other substances: solids may dissolve in a liquid, and solutions may also be formed of gas in liquid, or even liquid in liquid.
When a solution is formed, the solute is divided up by mixing with the solvent until it is in the form of individual molecules or ions, depending on what it is.
Solution concentrations can be measured either in terms of a mass per unit volume, as moles per litre, or as parts per million or billion, depending on need.
The maximum concentration of a solution can be predicted from basic information about the attractive forces involved in the solute and solvent.
Solubility relies on differences in attraction between the particles being dissolved on the one hand, and between the particles and the solvent on the other.
A colloid is not quite a solution, but it is not really a mixture either, given the size and even spread of the suspended particles that make up the colloid.
In 1848, Karl von Vierordt established that the osmotic pressure of a solution is always proportional to the concentration of solute in that solution.
Osmotic pressure refers to the force with which a concentrated solution draws water from a weaker one, or pure solvent, through a semi-permeable membrane.
Osmosis involves the flow of solvent from a less concentrated solution to a more concentrated one, through a semi-permeable membrane. The solute cannot pass.
An isotonic solution is one that has the same osmotic pressure as tissue placed in it, designed so that the cells of the tissue remain correctly hydrated.
Ringer's solution is an example of a standard isotonic solution. It is used to maintain tissues in a living state for experimental purposes and histology.
The observation of osmosis in action offers us clear evidence that atoms exist, since there is no other explanation for the effects that are seen and measured.
A polysaccharide is an example of a polymer: a variety of polysaccharides are used in living things to store carbohydrates without making hypertonic solutions.