Colloids and solutions are two mixtures that are commonly found in chemistry, and they have some distinct differences in their properties and appearance. Below I will go into detail on how to distinguish colloids from solutions.
First, we need to understand the definition of colloids and solutions. A solution is a homogeneous and transparent mixture formed by the dissolution of solutes in a solvent. There is no obvious interaction force between the molecules or ions of the solute and the molecules of the solvent, so they can move freely. Colloids, on the other hand, refer to mixtures of particles with particle sizes between 1 nanometer and 1000 nanometers, in which solutes are distributed in a solvent to form a suspension.
Next, we can distinguish colloids and solutions from the following aspects.
1.Exterior features:
The solution is usually transparent or translucent and does not show significant scattering or precipitation.
Colloids are often cloudy or milky white, sometimes yellow, blue, etc., because the particles in them can scatter light, making the colloids an observable cloudy state.
2.Filtration Test:
The solution can be filtered through ordinary filter paper or membranes to separate solid particles or other impurities.
Colloids cannot be separated by conventional filtration methods because their particle size is larger than the solvent molecules, so they are blocked by the filter paper or membrane.
3.Visibility test:
The visibility of the solution is usually good, and clear patterns or words can be seen.
Because the particles in the colloid scatter light, the light passing through the colloid will be disturbed, and the pattern will become blurry or difficult to identify.
4.Tyndall Scattering Test:
When passing through the solution, the light rays travel basically in a straight line and do not scatter.
When passing through the colloid, the light is scattered, resulting in a distinct Tyndall scattering phenomenon. This is because colloidal particles are similar to the wavelength of light, resulting in more pronounced scattering.
5.Dispersion stability:
The solute in solution is usually completely dissolved in the solvent to form a single phase and has good stability.
Because the particles are larger than the molecules, colloids will be suspended in the solvent and aggregate to form a duplex system, and they are prone to precipitation or agglomeration.
6.Particle Resolution Test:
The suspended particles in the solution are too small to be observed under a light microscope.
The particle size in the colloid is usually between a few nanometers and a few micrometers and can be observed under a microscope.
It is important to note that in some cases, the distinction between colloids and solutions can be difficult. For example, when colloidal particles are very small, almost as small as solute molecules, colloids may appear solution-like transparent. In this case, we need to use more advanced testing methods to determine the properties of the mixture.