what determines whether a mixture is a suspension, or a colloid?

Colloids don't settle out. Suspensions do.

To determine whether a mixture is a suspension or a colloid, there are a few factors to consider. The primary factors include the particle size, stability, and appearance of the mixture. Here's an explanation of each factor:

1. Particle size: Suspensions and colloids contain particles of different sizes. Suspensions have large particles that are visible to the naked eye and settle down over time due to gravity. These settleable particles make the mixture appear cloudy or opaque. In contrast, colloids have smaller particles, often in the range of 1-1000 nanometers, which are too small to be seen individually. This makes the mixture appear translucent or even transparent.

2. Stability: Another important factor is the stability of the mixture. A suspension is generally unstable, meaning the particles tend to settle due to gravity unless the mixture is constantly agitated. If left undisturbed, the larger particles in a suspension will eventually settle down, causing the liquid to appear clearer over time. On the other hand, colloids are relatively stable because their smaller particles are less likely to settle. The particles in a colloid remain dispersed and do not readily settle out, even when the mixture is left undisturbed for an extended period.

3. Appearance: The appearance of the mixture can provide visual clues to identify whether it is a suspension or a colloid. Suspensions appear cloudy or turbid due to the presence of visible particles that scatter light, making it difficult to see through the mixture. In contrast, colloids have a translucent appearance, as the dispersed particles are usually too small to scatter light significantly.

It is important to note that the classification of a mixture as a suspension or a colloid is not always straightforward, as there can be intermediate cases. These mixtures are known as emulsions. Emulsions are colloidal mixtures of two or more immiscible liquids, such as oil and water, where one liquid forms tiny droplets dispersed within the other liquid. Emulsions can exhibit characteristics of both colloids and suspensions, depending on the size and stability of the droplets.

To determine with certainty whether a mixture is a suspension or a colloid, several techniques can be employed, such as observing the settling of particles over time, using a microscope to examine particle size, or employing techniques like centrifugation to examine sedimentation behavior.