In chemistry, a dispersion is a mixture where one substance is distributed throughout another. These mixtures are common in daily life, from the air we breathe to the food we eat.
Understanding Dispersion
A dispersion is a heterogeneous mixture where one substance, the dispersed phase, is finely distributed within a continuous phase. The dispersed phase consists of discrete particles, droplets, or bubbles. Though appearing uniform, components maintain distinct identities microscopically and do not chemically react. Their distribution is achieved through physical forces, and the interaction and size of dispersed particles determine the dispersion’s characteristics.
Classifying Dispersions
Dispersions are categorized into three main types—solutions, colloids, and suspensions—based on the size of their dispersed particles. Each type exhibits unique properties directly related to this size.
Solutions are homogeneous mixtures with the smallest particle sizes, typically less than 1 nanometer (nm). Their molecular-sized particles are completely dissolved and uniformly distributed, making the mixture transparent and stable. Solutions do not settle over time and cannot be separated by filtration.
Colloids have intermediate particle sizes, generally ranging from 1 nm to 1000 nm. Though appearing uniform, they are heterogeneous mixtures with dispersed but not fully dissolved particles. These particles are too small to settle or be removed by simple filtration, yet large enough to scatter light.
Suspensions consist of the largest dispersed particles, exceeding 1000 nm. These clearly heterogeneous mixtures have visible particles that settle out of the continuous phase over time. Their larger size allows for separation by filtration.
Properties and Behaviors of Dispersions
The Tyndall effect is a notable phenomenon in colloids. It occurs when a light beam passes through a colloid, and dispersed particles scatter the light, making the beam visible. In contrast, light passes invisibly through true solutions.
Sedimentation is a characteristic behavior, particularly for suspensions. It is the process where dispersed particles settle to the bottom of the continuous phase due to gravity. This occurs because suspension particles are large and dense enough to be influenced by gravity, unlike those in solutions or colloids.
Filtration effectiveness varies significantly across dispersion types. Suspensions, with their large, undissolved particles, are easily separated by filtering. However, molecular-sized particles in solutions and smaller, stable particles in colloids pass through standard filters.
Dispersions in Everyday Life and Science
Dispersions are ubiquitous in daily life and various scientific disciplines. Many food items are complex dispersions, such as mayonnaise, an emulsion where one liquid is dispersed in another immiscible liquid.
Milk is a common colloid, with tiny fat globules dispersed in water. Fog and mist are also colloids, consisting of liquid water droplets dispersed in gas. Muddy water is a suspension, with soil particles dispersed in water before settling. Paint is another suspension, often requiring shaking to redistribute settled pigments.
In contrast, air is a solution, a homogeneous mixture of various gases like nitrogen and oxygen. Blood is a biological dispersion containing cells and proteins suspended in plasma. These examples highlight the diverse forms and widespread presence of dispersions in natural phenomena and manufactured products.