Please help me to answer these questions. I just need more insights about these.
ID: 1065363 • Letter: P
Question
Please help me to answer these questions. I just need more insights about these. Thank you so much!
Recrystallization Why do we do recrystallization? What makes a good recrystalization solvent? Why is it important to cool a recrystallization solution down slowly? Why should you use the minimum amount of solvent when doing a recrystallization? Extraction What is the purpose of doing an extraction? What are the requirements for solvents to be used as extraction solvents? What do we mean by chemically active extraction? What determines whether the organic layer will be the top layer or the bottom layer? Melting Point When recording a melting point (range), what visible changes occur that dictate when you record the start and finish of melting? What determines whether a melting point is acceptable? What affect does having impurity in the sample have on the melting point? Distillation What is the purpose of distillation? What equipment do you need to set up a distillation? What are the requirements for simple distillation to be successful? Gas Chromatography What is the purpose of G.C? How does it work? What variables can you manipulate on a G.C machine to change the retention time?Explanation / Answer
Recrystallisation is a method employed to purify the solid product obtained from a reaction. In order to obtain the compound in uniform, well-defined crystals, as well as to separate it from impurities like filter-fibres, inorganic substances, by-products, etc., it is dissolved, usually with the aid of heat, in a proper solvent, filtered from the impurities remaining undissolved, and allowed to cool gradually. The dissolved compound then separates out in a crystallised form, while the dissolved impurities are retained by the mother-liquor. The choice of solvent is critical to the purification by recrystallisation. One essential characteristic of a useful solvent is that the desired compound must be considerably more soluble in the solvent when it is hot than when it is cold. At times the separation of crystals takes place suddenly, the crystals thus obtained are generally not well formed. Slow cooling allows the generation of good quality crystals. Recrystallization involves dissolving in a minimal amount of hot solvent so that the solution is saturated with the product crystals, so that the crystals come out of solution, leaving the impurities dissolved in the solvent easily.