The key differences between a suspension and a colloid lie primarily in particle size, stability, and optical properties:
- Particle Size:
Suspensions have larger particles, typically greater than 1000 nanometers (1 micrometer), which are visible to the naked eye. Colloids have smaller particles, generally in the range of about 1 to 1000 nanometers, which are not visible without a microscope
- Stability and Separation:
In suspensions, the large particles tend to settle out over time due to gravity if left undisturbed, making the mixture heterogeneous and easily separable by filtration or settling. In contrast, colloidal particles do not settle on standing because their small size and Brownian motion keep them dispersed evenly. Colloids are stable and cannot be separated by ordinary filtration, though they can be separated by special methods like centrifugation
- Optical Properties:
Colloids exhibit the Tyndall effect, meaning they scatter light, making a beam of light visible as it passes through. Suspensions do not transmit light well and do not show this effect; they appear opaque or cloudy
- Homogeneity:
Suspensions are heterogeneous mixtures where components can be distinguished, while colloids appear more uniform or homogeneous to the naked eye despite being heterogeneous at the microscopic level
In summary, suspensions contain larger, visible particles that settle out and can be filtered, whereas colloids have smaller particles that remain evenly dispersed without settling and scatter light, making them stable mixtures intermediate between true solutions and suspensions.
