What is a Chemical Suspension?
In chemistry, a suspension is a heterogeneous mixture where solid particles are dispersed in a fluid (a liquid or a gas) but are large enough that they will eventually settle out over time due to gravity. Unlike a solution, the particles in a suspension do not dissolve in the solvent, and unlike a colloid, they are not permanently dispersed.
Key Characteristics of Suspensions
Suspensions exhibit distinct characteristics: their dispersed particles are generally visible to the naked eye, making the mixture opaque or cloudy. These particles are larger than those found in solutions and colloids, typically greater than 1000 nanometers. Due to their size, the solid particles will settle out of the fluid if the suspension is left undisturbed. Furthermore, the components of a suspension can usually be separated by simple physical means, such as filtration or decantation.
Practical Examples of Suspensions
Common examples of suspensions include muddy water, where soil or clay particles are mixed with water but will eventually sink to the bottom. Sand mixed in water also forms a suspension. Many pharmaceutical preparations, such as liquid antacids or some antibiotic syrups, are suspensions; this is why their labels often instruct you to 'shake well before use' to redistribute the settled solid medication particles evenly.
Distinguishing Suspensions from Solutions and Colloids
The key difference lies in particle size and stability. In a solution, particles are individual molecules or ions, perfectly dissolved and invisible, and will never settle. Colloids have particles larger than solutions but smaller than suspensions (1-1000 nm), which remain dispersed and don't settle due to Brownian motion, often exhibiting the Tyndall effect (scattering light). Suspensions, with their large, settling particles, represent the least stable type of mixture among the three.