What is a chemical suspension?

We explain what a suspension in chemistry is, its phases, characteristics and properties. In addition, experiments with suspensions.

1. What is a chemical suspension?

In chemistry , suspension means a type of heterogeneous mixture consisting of small particles of a solid dispersed in a liquid medium in which it cannot dissolve. The name suspension comes from the fact that the particles are suspended. That is to say that the solid does not dissolve in the liquid , even if it is microscopic particles.

All suspensions, then, are made up of:

• Dispersed phase : It is the solid phase.
• Dispersant phase : Also called continuous or external, it is the liquid phase.

In addition, they usually contain surfactants , which are dispersing agents, whose role is to prevent solids from agglutinating or sedimenting; and even stabilizing substances, which keep the suspension in balance. These last two elements are fundamental in the industrial production of this type of compounds.

They are very useful in various industries and are the fundamental principle behind the spray. For example, a fruit juice is an example of a suspension, since the solid pulp is suspended in the water, but if given enough time, it will decant by gravity , towards the bottom of the container. But if we shake it, it recovers its properties temporarily.

2. Properties of a suspension

The suspensions are, for the most part, not very stable . This is because solid particles can be distributed homogeneously in the continuous phase without agglutinating or sedimenting only for a certain time.

The period of stability depends essentially on the viscosity of the continuous phase (the higher the viscosity, the longer), the size of the dispersed particles and the temperature at which the compound is . In addition, stabilizing or anti-caking additives that maximize the period of stability are usually used.

On the other hand, the suspensions may seem inseparable, but given enough time it is possible to decant both phases allowing the solids to settle. In addition, they can be completely separated only by specific filtration or centrifugation methods .

Another interesting property of suspensions is that they can act as solids under certain circumstances, and as liquids in others . Thus, they can flow like liquids, but offer some hardness to impacts as solids do.

3. Emulsion and suspension

Emulsions and suspensions are somewhat similar. The former are also heterogeneous mixtures of phases that do not 100% interconnect, but which in this case are both liquid, that is, an emulsion is a heterogeneous mixture of immiscible liquids .

Temporarily, these two liquids are indiscernible from each other, but if given enough time, they will separate as is the case with the suspensions. Of course: unlike emulsions, suspensions do not have a specific color .

4. Suspension Experiments

Next, we will explain a couple of homemade experiments to demonstrate the properties of the suspensions:

• Cornmeal suspension

You will need : 1 cup of flour or cornstarch, 1 bowl, about ½ cup of water, a spoon, a foot plate.

Instructions : Pour the flour or cornstarch into the large bowl, and slowly add the water while stirring with the spoon. Do not add all the water if it is not necessary. Once you get an aqueous consistency, hold the mixture with your hands and watch it spill. Then hit the suspension with one hand and observe how it resists, as if it were a solid. Pour unmixed water on the foot plate and try to repeat the sensations: hold it, and hit it. Record the differences between the liquid and the suspension.

• Talcum suspension

You will need : 2 tablespoons of talcum powder, a glass of water, a spoon.

Instructions : Pour the talc into the glass of water gradually, while stirring with the spoon, until you get a uniform mixture. Take note, if any, of the solid remains at the bottom of the glass. Place the glass in a place where nobody touches it and is at rest. Come back after 5 minutes. Take note, if any, of the solid remains on the floor of the glass. Repeat the procedure at 10, 15, 20 and 30 minutes, to observe how the suspended solids settle at the bottom, separating the two phases.