Mixtures form when different substances combine, and their properties depend on how the components interact. Not all mixtures are alike, as some blend seamlessly while others maintain distinct characteristics. Understanding these differences helps to classify matter and predict its behavior.
Understanding True Solutions
A true solution is a homogeneous mixture where one substance, the solute, dissolves into another (the solvent). Examples include sugar dissolved in water or salt in water. The particles in a true solution are extremely small, typically less than 1 nanometer (nm) in diameter.
True solutions are transparent because their particles are too small to scatter light and do not exhibit the Tyndall effect. These mixtures are stable, and the dissolved particles do not settle out over time. The components of a true solution cannot be separated by simple filtration.
What Are Suspensions?
A suspension is a heterogeneous mixture of solid particles dispersed in a liquid or gas that eventually settle out. These particles are larger than those in solutions, typically exceeding 1000 nm (or 1 micrometer) in diameter. Their large particle size often makes them visible to the naked eye, giving suspensions a cloudy or opaque appearance.
Particles in a suspension settle over time due to gravity if undisturbed, which is why some liquid medications require shaking before use. Suspensions can be separated by simple filtration. Common examples include muddy water, sand in water, orange juice with pulp, and certain paints. Suspensions can scatter light, but this property is not as consistent as in colloids, and they become transparent once particles settle.
What Are Colloids?
A colloid is a heterogeneous mixture of very fine particles dispersed evenly throughout another substance. These particles are intermediate in size, ranging from approximately 1 nm to 1000 nm in diameter. Despite being heterogeneous, colloids often appear homogeneous to the naked eye due to their small size and even distribution.
A distinguishing property of colloids is the Tyndall effect, where dispersed particles scatter light, making the light beam visible. Unlike suspensions, colloidal particles do not settle out over time and cannot be separated by simple filtration. Everyday examples of colloids include milk, fog, smoke, paint, gelatin, and mayonnaise.
Distinguishing Suspensions and Colloids
The main difference between suspensions and colloids is particle size. Colloids have particles between 1 and 1000 nm, while suspensions have particles larger than 1000 nm. This size difference dictates many of their observable properties. Suspension particles settle over time due to gravity, leading to phase separation if undisturbed. Colloidal particles, in contrast, remain dispersed indefinitely and do not settle.
Appearance also differs: suspensions are typically opaque or cloudy with visible particles, while colloids can appear translucent or even clear, despite being microscopically heterogeneous. Filtration effectively separates the components of a suspension, but colloids cannot be separated by standard filtration methods. The Tyndall effect is a key diagnostic tool: colloids consistently scatter light, making a light beam visible. True solutions do not, and suspensions may or may not, depending on particle concentration and settling. Understanding these distinctions is useful for various applications, from pharmaceutical formulations to food science.