Question

Sophia and her friend Nora have the same unknown solid. Sophia has progressed a little faster with the purification process, but now she is standing around twiddling her thumbs because no crystals are forming, even over an ice bath. Nora decides that Sophia’s problem is too much solvent. Determined not to have the same problem, Nora uses a minimal volume of hot solvent to dissolve her compound before doing the gravity filtration step. She begins to pour her hot solution into the filter cone of a long-stemmed funnel and ….is that missed impurities sprouting up on the funnel walls? Why so shiny? Explain what Nora did wrong and how to fix the problem.

Answer 1

Nora used a minimal volume of hot solvent, resulting in a supersaturated solution and the shiny impurities on the funnel walls. To fix the problem, she should use a larger volume of hot solvent to dissolve her compound.

Step-by-step explanation:

Nora's problem is that she used a minimal volume of hot solvent when dissolving her compound. This resulted in a supersaturated solution, where the compound was dissolved in excess and could not fully crystallize out. The shiny impurities on the funnel walls are excess solute that did not precipitate.

To fix the problem, Nora should use a larger volume of hot solvent to dissolve her compound. This will ensure that the solution is not supersaturated and allow the compound to fully crystallize out during the cooling process.

Answer 2

Nora used a minimal volume of hot solvent, this hot mixture was filtered to remove insoluble impurities. She had to perform a rapid filtration with a minimum of evaporation in a short-stemmed funnel previously heated in an oven, and provided with a pleated filter to increase the filtration rate, so in this way she prevented the product from crystallizing prematurely on the funnel stem.

If with this technique does not reach a pure substance, the process can be repeated by heating the solvent, changing the funnel or looking for a solvent with high dissolution power of the substance.

Step-by-step explanation:

The solid products obtained in a reaction are usually accompanied by impurities that must be removed in order to dispose of the desired product in the highest possible purity. The most suitable method for removing impurities that contaminate a solid is by crystallization either in a pure solvent or in a mixture of solvents. This procedure is given the generic name of recrystallization.