CHEM 121 LAB EXAM QUESTIONS WITH COMPLETE SOLUTIONS VERIFIED LATEST UPDATE 2024
Given a gram of a 1:1 mixture benzoic acid and cholesterol, describe how you would separate the two compound.
1. In a separatory funnel, dissolving each in ether. Add a base.
Organic layer will contain the ether
...
Given a gram of a 1:1 mixture benzoic acid and cholesterol, describe how you
would separate the two compound.
1. In a separatory funnel, dissolving each in ether. Add a base.
Organic layer will contain the ether
Aqueous layer will contain the acid
Benzamine and cholesterol are dissolved in ether. How would you separate
them?
Place into a separatory funnel and add a strong acid
Organic layer will contain ether
Aqueous layer will contain the acid
a) What are the properties of a good recrystallization solvent.
b) When would you use a mixed recrystallizing solvent system rather than an
single solvent system.
1. a) @ room temp, solvent should not dissolve
@ boiling temp, solid should completely dissolve
Should have boiling point lower than melting point of solid that is being purified
Solvent should not react with solid being purified
b) When a single solvent wont work
Why use a Buchner funnel to collect crystals rather than gravity filtration
apparatus?
Vacuum filtration is more efficient when the solid is the desired material (i.e. removing
the solvent from the crystals)
, A compound dissolves readily in ether at room temperature and not at all in water
are room temperature . Why is ether and water still not able to be used for a mix
solvent recrystallization?
The compound must be soluble in water at room temp as well
Given a list of reagents, give the products of the reaction ( covered in the lab
a) dehydration
b) bromination
a) 1-methylcycohexene, 3-methyl-1-cyclohexene, 4-methy-1-lcyclohexene,
methylenecyclohexene, ethylidenecyclopentene
b) 1,2-dibromo-1,2-diphenylethane
Draw the mechanism for the dehydration and bromination reactions. Use correct
arrow, and show all intermediates.
Refer to Photos
After the reaction, a product was distilled. The distillate was placed in a
separatory funnel and washed with NaCl (sat) . Why was the distillate washed
with brine?
The brine pulls the remaining water from the organic layer to the aqueous layer.
Given the density , molecular weight and the volume or mass of reagents:
a) calculate the mols of reagent, equivalence and determine the limiting reagent.
b) given the product yield -calculated the % yield.
a) use starting material to find common product and use the lowest amount created as
limiting reagent
What is a catalyst
Substance that increases the rate of a reaction without being used up by lowering
activation energy (Ea).
What is indicated by melting point range.
Point at where it's beginning to liquify and indicates identity and purity
a) What is indicated by melting point depression.
b ) Given a number of standard compound that have the same melting point as
your product - What techniques could you use to give PROOF of the identity of
your product?
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