Suspensions: Definition and Properties

Definition

A suspension is a heterogeneous mixture containing solid particles that are large enough for sedimentation. These particles are dispersed throughout a liquid but are not dissolved. Over time, the solid particles will settle out due to gravity.

Explanation

Unlike solutions, where the solute is dissolved and the particles are molecularly dispersed, the particles in a suspension remain as larger aggregates. This means you can often see the individual particles. Suspensions are unstable mixtures, as the dispersed particles will eventually separate from the liquid phase. Filtration can typically separate the solid particles from the liquid.

The size of the dispersed particles is crucial. Particles in suspensions are generally larger than 1 micrometer (µm).

Properties of Suspensions

Heterogeneous: Suspensions are not uniform throughout and have visible differences between the dispersed phase (solid) and the continuous phase (liquid).
Unstable: Particles will settle out over time due to gravity.
Large Particle Size: Particles are relatively large, typically exceeding 1 µm, and can be seen with the naked eye or a microscope.
Filtrable: Solid particles can be separated from the liquid using a filter.
Tyndall Effect: Suspensions exhibit the Tyndall effect, meaning they scatter light, making a beam of light visible as it passes through the mixture.

Examples

Muddy water (soil particles suspended in water)
Paint (pigment particles suspended in a liquid)
Milk of magnesia (magnesium hydroxide particles suspended in water)
Blood (cells suspended in plasma)
Flour in water

Common Misconceptions

Misconception: Suspensions are the same as solutions.
Reality: Solutions have dissolved particles, while suspensions have undissolved, larger particles. Solutions are homogeneous and stable; suspensions are heterogeneous and unstable.
Misconception: All mixtures appear clear.
Reality: Suspensions are often cloudy or opaque due to the scattering of light by the suspended particles.

Importance in Real Life

Medicine: Many medications are suspensions, such as antibiotics and antacids.
Construction: Paints and cement mixtures are suspensions.
Agriculture: Insecticides and herbicides are often applied in suspension form.
Environmental Science: Understanding suspensions is crucial for studying water pollution and sedimentation processes.

Fun Fact

The stability of a suspension can be improved by adding a stabilizing agent (e.g., a surfactant or emulsifier) to prevent the particles from settling too quickly.

History or Discovery

The concept of suspensions has been understood for centuries, particularly in areas like pottery and dyeing. Early civilizations observed and utilized the settling properties of particles in liquids to separate materials or create specific effects.

FAQs

What is the difference between a suspension and a colloid?

Both suspensions and colloids involve dispersed particles in a continuous phase. However, in colloids, the particles are smaller (typically 1-1000 nm) and remain suspended for longer periods. Colloids also exhibit the Tyndall effect, but are generally more stable than suspensions. Suspensions particles are larger, and settle out faster.

How can you separate the components of a suspension?

The components of a suspension can be separated by filtration, sedimentation, or centrifugation. Filtration is generally the easiest method.

Does temperature affect a suspension?

Yes, temperature can affect the settling rate of a suspension. Higher temperatures often decrease the viscosity of the liquid, potentially leading to faster settling. Temperature changes can also affect the solubility of components and particle interactions.