Q1.
Let us try to understand what colloids are. How are they different from solutions and suspensions?
Answer
A colloid is a mixture in which particles of one substance, sized between 1 nm and 1000 nm, stay evenly dispersed through another substance without dissolving and without settling.
| Property | Solution | Colloid | Suspension |
|---|---|---|---|
| Nature | Homogeneous | Heterogeneous (looks homogeneous) | Heterogeneous |
| Particle size | Less than 1 nm | 1 – 1000 nm | More than 1000 nm |
| Particles visible? | No | No | Yes, to the naked eye |
| Separated by filtration? | No | No | Yes |
| Settles on standing? | No | No | Yes |
| Tyndall effect | Not shown | Shown | Shown |
The components of a colloid have their own names: the solute-like dispersed particles form the dispersed phase, and the substance they are spread through is the dispersion medium.
Why the colloid is the interesting middle case: Its particles are small enough that random molecular bombardment keeps them permanently suspended, so like a solution it never settles and passes through filter paper. But they are large enough to scatter light, so unlike a solution it shows the Tyndall effect and is really a two-phase, heterogeneous mixture. Size alone explains every entry in the table.