Why do suspended particles settle in muddy water over time but not in milk?
Muddy water is a suspension, whereas milk is a colloid. The primary difference in their behavior over time is due to the size of their particles.
In muddy water, the particles are large-sized (more than 1000 nm in diameter). Because of their large size, these heavier particles settle down at the bottom when left undisturbed.
In contrast, milk contains moderate-sized particles (1–1000 nm in diameter). Since these particles are much smaller, they do not settle over time and remain uniformly dispersed throughout the mixture.
Explanation
The textbook context highlights that the settling of particles depends on the type of mixture, which is determined by particle size. Suspensions like muddy water have large particles (>1000 nm) that settle under gravity when undisturbed. Colloids like milk have smaller particles (1-1000 nm) that do not settle over time and remain uniformly dispersed, behaving more like a solution in that regard.