Q1: Agitator is provided in a crystalliser for

ANS:D - all (a), (b) and (c).

Certainly!

1. Avoiding deposition on cooler surfaces: In a crystallizer, if certain regions become cooler than others, solute molecules may precipitate out and deposit onto these cooler surfaces. This uneven deposition can lead to inefficient use of the solute and uneven crystal growth. Agitation helps in maintaining a uniform temperature distribution throughout the solution, preventing localized cooling and the subsequent deposition of solute on cooler surfaces.
2. Formation of nuclei: Nucleation is the process by which solute molecules or ions come together to form the initial clusters or nuclei of crystals. Agitation promotes the dispersion of solute molecules or ions in the solvent, increasing their chances of coming into contact and forming nuclei. By ensuring that solute molecules are uniformly distributed throughout the solution, agitation facilitates the nucleation process and promotes the formation of crystals.
3. Crystal growth: Once nuclei are formed, they can grow into larger crystals through the addition of solute molecules or ions from the surrounding solution. Agitation prevents the crystals from settling at the bottom of the crystallizer by keeping them suspended in the solution. This ensures that all crystals have equal access to solute molecules or ions, promoting uniform crystal growth throughout the solution. Additionally, agitation can help break up larger crystals into smaller ones, leading to more uniform crystal size distribution.

In summary, agitation in a crystallizer serves multiple purposes: it prevents uneven deposition of solute, promotes the formation of nuclei, and facilitates uniform crystal growth. These functions are essential for achieving efficient and controlled crystallization processes.