organic chemistry 1 ps/blackboard/execute/contentfile?cmd=view/&content;_id-2058
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organic chemistry 1
ps/blackboard/execute/contentfile?cmd=view/&content;_id-2058950-1 &course-id;:57 Questlons 1. How would a mixture of naphthalene and benzophenone behave on a TLC plate with hexanes/ acetone as the eluent? Compare the polarity of these two compounds Outline the most commonly used procedure for the purification of an impure solid material using the technique of recrystallization. 2. 3. Why is acetone such a popular solvent? Point out one drawback in terms of safety consid- 4. Your final product might be impure since you suspect decomposition might have occurred. S. Why is it important to use a minimal amount of hot solvent during a recrystallization? What erations. When determining the melting point of your product, what are you looking for? would happen if you used too much solvent while dissolving your solid? 6. nt to cool the dissolved product/solvent mixture slowly during a recrystal- lization? 7. Discuss the melting point range characteristics of a pure and an impure sample. An accurate melting point range can be obtained by heating the sample quickly just as well as if obtained by allowing the temperature to rise slowly. True or false? Explain. 8. 9. What is the first indication of a sample melting in the melting point tube? 10. Suppose your sample melts before you are ready to record the melting point. Should you a) cool the capillary and redetermine the mp or b) begin with a fresh sample? Explain ^Explanation / Answer
1) Napthalene is less polar; therefore it travels further than benzophenone which is more polar.
Benzophenone is more polar than naphthalene because it has a carbonyl. Naphthelene is basically non-polar.
2) Solid is dissolved in solvent boil it at medium setting Allow solution to cool down. Crystals are formed.Filtration is used to separate crystales from solvent.You can check impurities because impurities lower melting point.
Recrystallization is one of the most important techniques for an organic chemist to know. It is a method for purifying solid compounds which are frequently the products of organic reactions. The theory of recrystallization is based on three important concepts:
A compound is always more soluble in hot solvents than in cold solvents.
(i) Molecules have unique solubility properties.
(ii) A growing crystal will only accept similar entities into its lattice.
3) Acetone is polar and dissolves substances because its polar (polar end quickly attach to atoms). The drawback is that its extremely flammable.
4) The melting point helps determine if to tell if impurities exist because a lower melting point than normal shows that impurities still exist.
5) Using the minimum amount minimizes the amount of material lost by retention in the solvent.
so Dissolve in minimum amount of hot solvent to ensure solution is saturated (watch carefully). If too much solvent is added, evaporate solvent to point of saturation. If not saturate, not much will come out of solution (lower % recovery).
6) Because they are allowed to settle down more slowly and make more prominent crystals.
7) Impurities widen the range of Melting Point in a sample (MP tells you how pure the product is, if all other factors are kept as a control. smaller mp ranges=more purity)
8) False
because by going slower you can be more accurate.If you heat the mixture too quickly, you won't be able to tell exactly at which temperature it started and completed melting.
9) Small particles on the side moving (turning into liquid), dis-shaping, discoloration "when a droplet appears"
10) you should start over with a fresh sample because the process of melting then cooling then melting again may produce inaccurate, dislocated molecules if boiling point is close to mp then evaporation may occur Old sample may contain impurities/decomposition.
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