(a) Colloidal solutions show Tyndall effect but true solutions do not. Discuss.
(b) Explain how does soap help in cleaning dirty clothes ?

Explanation

(a) In a colloidal solution, the particle size is such (1 nm to 100 nm), that these particles scatter the light rays as they fall on them. Because of scattering, the path of the light as well as the particles become visible. But in a true solution, the particle size is so small (less than 1nm) that these particles are not in a position to scatter the light. Therefore, true solution does not show any Tyndall effect.
(b) In dirty clothes, the dust particles are sticking on the oil drops present. Simple water cannot remove these oil drops from the clothes because water and oil as such do not form a stable emulsion. Soap plays the role of emulsifier and helps in forming a stable emulsion between the two. In other words, it helps in mixing oil and water. This means that soap helps in removing these oil drops along with the dirt sticking to them. The dirty clothes get washed by soap solution.