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Tomorrow I have a science test, and in it there are some mixtures, and we have to identify whether they are a solution, a suspension or a colloid. Is there an easy way we can identify this WITHOUT getting the mixtures up and seeing whether they sediment or not?
Note: They are everyday mixtures, like lattes, freshly squeezed orange juice etc.

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If the solute particles are very small ($\ce{< 1nm}$), then they form a true solution.

If the solute particles are very large ($\ce{1nm < size < 1000nm}$), then they form a collidal solution.

If the solute particles are very large ($\ce{ > 1000nm}$), then they form a suspension.

The numbers are not exact; they are approximate border ranges. A particle with size $\ce{1100nm}$ can form a colloidal solution. The questions given in your test will give the samples whose size lie in the middle range. Otherwise, it is quite difficult to determine what type of solution they will form; it has to be determined experimentally.

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If the analyte happens to be in a transparent container, shine light on it, see if the light is scattered (Tyndall effect) -- if so, you have either suspension, or colloidal matter. Instead of a laser pointer, a good pocket light (like the ones with halogen bulb halogen or LEDs) may be used as light source, too.

enter image description here

(source)

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  • $\begingroup$ It's a test. We cannot come to class with bottles of mixtures $\endgroup$ – bio Apr 3 '17 at 10:55
  • $\begingroup$ If you point an intense light source to the surface of the liquid (either solution, colloïdal mixture) you may see if the light beam passes across the medium "without a trace", or if you observe a milky / foggy scattering that resembles more or less an illuminated rod (like above left hand example) if seen from the side. The picture above is more visual in comparision, of course, but even for the bottle of $\ce{CoCl2}$ soluted in water you see a deposit. If the test is tomorrow, familiarize yourself with milk, as one example of colloids. The "fog" is visible even without lifting the jar. $\endgroup$ – Buttonwood Apr 3 '17 at 11:08

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