Final answer:
Colloidal particles cannot be separated by conventional filtration because they are too small and do not settle out like the particles in suspensions. Instead, a semipermeable membrane must be used to separate colloids from a mixture via a process called dialysis, utilizing the Tyndall effect to distinguish colloidal particles from those in true solutions.
Step-by-step explanation:
Colloids, which are mixtures where one substance is dispersed evenly throughout another, have particles that are too small to be filtered through conventional filtration methods. Unlike a suspension, colloids do not settle when left undisturbed, and their particles are not retained by standard filter paper. An example of a colloid is milk, which appears homogeneous but contains dispersed fat and protein particles. Colloidal particles can scatter light, known as the Tyndall effect, which makes them distinct from true solutions whose particles do not scatter light.
To separate colloidal particles, a method like dialysis is utilized. Dialysis involves the use of a semipermeable membrane, which allows small molecules and ions to pass through but retains larger colloidal particles such as proteins or starches. The process of dialysis can be visualized in figures such as 9.11.1 and 5.5.6, which demonstrate how the semipermeable membrane selectively allows certain molecules to be separated based on size.
In contrast, filtration is effective for separating mixtures of solids and liquids where the solid particles are significantly larger, such as sand in water. However, because colloidal particles are smaller and don't settle out, filtration is not an effective method for separating colloidal mixtures.