Chemistry 212 - Lab Exam

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Chemistry 212 - Lab Exam

• given a gram of a 1 ANS1 Mixture of benzoic acid and cholesterol, how

would you separate the 2 compounds? ANS 1. Dissolve both compounds in ether in a Sep Funnel (both are ether soluble)

• Add Base (NaCO3) to hydrolyze
• Conjugate base (benzoic acid) is now charge and enters aqueous layer
• Cholesterol = neutral, in organic layer

• Benzamine and cholesterol are dissolved in in ether. How would you sepa-

rate? ANS 1. Add to sep funnel

• Add strong acid
• Benzamine is basic and enters aqueous layer
• cholesterol in organic layer

• Properties of a good recrystallization solvent ANS 1. At room temp wont

dissolve solid

• At boiling will dissolve solid
• Solvent BP is lower than solids
• Sufficiently volatile
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• When would you use a mixed recrystallizing solvent system instead of a

single solvent system? ANS When one solvent doesn't have all the required properties for recrystallization

• Why use a Buchner funnel (vacuum filtration) to collect crystals rather than

gravity filtration? ANS Vacuum filtration is faster and better at collecting a desired solid from material

• A compound dissolves readily at room temp in ether but not at room temp

in water. Why is an ether water solvent mixture still not usable for recrystal- lization? ANS The compound has to be soluble in water at room temp as well

• given the reagents, give the products of the reaction (dehydration and

bromonation) ANS Look at pictures drawn

• Draw the mechanism for dehydration of bromination and dehydration ANS

Look at pictures drawn

• Why was the distillate washed with brine? ANS To pull any remaining water

from organic into the aqueous layer

• How do you determine a limiting reagent ANS 1. Balance reaction
• Convert info given into moles
• Use stoich for each reactant to find product mass produced
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