Objective: To differentiate between solutions and suspensions
Unopened can of clear carbonated beverage
Other samples of soda
Place a transparent cup on the overhead projector.
Quickly open the can of clear soda and pour it into the cup. The projected image will initially turn black, then eventually turn clear!
Illuminate cups of soda, milk and muddy water on the overhead.
This demonstration graphically illustrates the difference between a solution and a suspension. A solution is a homogeneous mixture with only one phase. It will never settle out, and will always be transparent. A suspension is heterogeneous, having two or more distinct phases. Muddy water is a temporary suspension, where the dispersed particles will eventually settle to the bottom. Substances like milk are also suspensions, since particles are dispersed rather then dissolved.
On the overhead, solutions will appear transparent, since the dissolved particles are so small that light can easily pass through the solution. Colas, coffee, and Kool-Aid will appear transparent on the overheard, proving that light can pass through them and that they are true solutions. Substances like milk and muddy water contain much larger particles, which do not allow light to pass. These substances are suspensions, not solutions.
When the can of clear soda is poured into the cup on the overhead, the projected image will at first appear black, because of bubbles coming our of the solution. At this point, the soda is not a solution, since there are two separate phases – a liquid and a gas.
As soon as the bubbles dissipate, however, the soda appears clear. It is interesting to note that before the can is opened, the soda is a true solution, since the CO2 is dissolved in the liquid. Upon opening, the bubbles begin to come out of the solution, due to reduced pressure, forming a heterogeneous mixture.