CHEM 232 Study Guide - Midterm Guide: Column Chromatography, Separatory Funnel, Seed Crystal
26 Mar 2018
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What is the purpose of the seed crystal or scratching at the bottom of the flask: to i(cid:374)itiate re(cid:272)rystallizatio(cid:374) if it does(cid:374)"t o(cid:272)(cid:272)ur o(cid:374) its ow(cid:374). If you recrystallize 1. 87 g of an unknown solid and recover 1. 23 g of crystals, what is the percent recovery: 1. 23/1. 87=65. 8% Be able to calculate minimum amount of solute needed (solubility rules) to perform a recrystallization. Be familiar with solubility of solids in solvents and how to increase the yield. Mixed melting points cannot be 50:50 ratios. One has to be greater because otherwise there is no way to tell which is the impurity. Hot gravity filtration vs vacuum filtration: hot gravity- removes solid impurities, vacuum- removes liquid impurities/excess solvent. Impure solid melting range vs pure solid: range is lower and broader than pure substance. Tlc plate purity determined by number of spots in a lane. How do you determine which layer will be on top of the separatory funnel: density.
