my definition of solution is a homogenous mixture of a solute and solvent.

and in my textbook they call colloids and suspensions solutions . how is this possible if both of them are heterogenous mixtures.


2 Answers 2


The definition of solution is a little bit cloudy. IUPAC define a solution in this way:

A liquid or solid phase containing more than one substance, when for convenience one (or more) substance, which is called the solvent, is treated differently from the other substances, which are called solutes.

And indeed this is a quite general approch that takes in account that we usaually call solutions systems (such as metallic solution) that are not compose of single molecules or ions dissolved in a solvent. Besides this approch chemists generally call solution a system with the folowing charachteristics:

  • It is stable.
  • It has only one phase.
  • It has to be an homogeneous mixture of two or more substances.
  • The solute can't be distinguished from the solvent (no scattering, can't be filtered)

And so I would not define colloids and suspension solution because they have a dispersed phase and often they are not stable.


Reducto ad absurdum, all matter is discrete, none is "homogeneous". So, there are no "homogeneous" solutions, since not only are there no solutions without particles present, but there are no solutions which contain exactly the same number of atoms in every cubic volume element. You may be thinking that my argument is silly, and you wouldn't be wrong. OTOH, your definition uses the words "solute" and "solvent" which is quite useless (circular definitions are really not appropriate nor necessary here). The only information you give us in it, is that the mixture must be homogeneous - which you don't define. Did you know that you can take a solution of some heavy metal salts, and centrifuge them and concentrate the salts at the bottom? So, the idea that there is a single criteria you can use to separate dispersions from solutions is incorrect - it changes with context. To be perhaps a bit clearer, some would consider colloidal mixtures, and even suspensions to be "homogeneous enough" to be "solutions". Generally, a colloid has a lot of interactions between its surface and the solvent, so that it makes sense in some contexts to call it a solution. I'm less enthused about calling a suspension a "solution", I'd call it a dispersion. Bottom line here is that "phases" are macroscopic things, and both suspensions and colloids are microscopically distributed, so a mixture of either may for some purposes be considered homogeneous. This is about terminology. I won't say its a bad question, but I will point out that this type of question ultimately depends on definitions, so may not be useful to worry about. (I decided not to "go there" as far as inquiring what qualifies you to say "my definition" - generally, you should be widely published in the appropriate area, and even experts may use terminology differently. This question isn't about things, its about words. It would be more interesting if YOUR definition was obtained from the text book, in which case it would seem to be inconsistent. I have no problem with the fact that the usage in the textbook is different than what you've seen elsewhere.


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