Suspension
Definition and meaning of Suspension in chemistry.
A suspension is a heterogeneous mixture where solid particles are dispersed throughout a liquid or a gas. These solid particles do not actually dissolve into the surrounding fluid. Instead, they are large enough that they will eventually settle out completely due to gravity.
In more detail
In everyday language, a suspension might mean pausing an activity or hanging something from a ceiling. In chemistry, a suspension has a very specific physical meaning. It differs fundamentally from a true chemical solution like saltwater.
In a solution, solute molecules dissolve completely and become entirely invisible. In a suspension, the solid chunks remain physically distinct from the surrounding liquid phase. These suspended solid particles are typically larger than one micrometer in diameter.
This relatively large size makes them visible under a simple microscope or even to the naked eye. Because the floating particles are so large, they constantly block and scatter incoming light. This light scattering causes the entire mixture to appear opaque or cloudy rather than crystal clear.
Gravity continuously pulls down on these relatively heavy solid particles. If you leave a suspension undisturbed on a laboratory table, it will eventually separate. The solid pieces will slowly drift downward and settle at the bottom of the container.
You can easily separate the solid from the liquid using simple physical methods. Pouring the cloudy mixture through a paper filter will cleanly trap the large solid particles. You can also use a rapidly spinning centrifuge to force the heavy particles down much faster. Students often confuse suspensions with colloids, but colloid particles are much smaller and never naturally settle.
Key facts
| Field | General Chemistry |
|---|---|
| Mixture Type | Heterogeneous mixture |
| Particle Size | Greater than 1 micrometer in diameter |
| Optical Property | Opaque or cloudy due to light scattering (Tyndall effect) |
| Separation Methods | Gravity settling, physical filtration, or centrifugation |
| Common Examples | Muddy water, liquid medicines that require shaking, airborne dust |
Vigorously mixing dirt and water creates a classic chemical suspension known as mud. The dirt particles swirl around in the water but completely fail to dissolve. Over time, the heavy dirt inevitably settles to the bottom of the glass. You can easily separate this temporary mixture by pouring the liquid through a paper filter.
Frequently asked questions
How is a suspension different from a solution?
In a solution, the solid dissolves completely to form a perfectly clear, uniform mixture. In a suspension, the solid particles do not dissolve at all. They remain visible and create a cloudy mixture that will eventually separate.
How is a suspension different from a colloid?
Both are heterogeneous mixtures that can look cloudy. However, suspensions have larger particles that visibly settle at the bottom over time. Colloid particles are much smaller and remain permanently floating without ever settling.
Why do some liquid medicines say 'shake well before using'?
These liquid medicines are actually chemical suspensions. The active medicine particles slowly settle to the bottom of the bottle while sitting on the shelf. Shaking the bottle mixes the particles back evenly before you measure a dose.