Answer the following questions (omit the questions in the Chem. 261 lab manual).
ID: 976358 • Letter: A
Question
Answer the following questions (omit the questions in the Chem. 261 lab manual). Esterification reactions are in equilibrium at every step. List two things you can do to help drive the reaction toward the desired ester product. What is the point of adding aqueous sodium bicarbonate in this week's experiment? Explain. Why is it necessary to ensure that all connections are tight and the O-rings in place when the ester is distilled? Why is it easier to remove excess acetic acid from the products than excess isopentyl alcohol?Explanation / Answer
a.) It is important to note that this is a reversible reaction, so the acid and alcohol reactants and ester products are in equilibrium (implied by the double arrow). What this means is that once the reaction reaches equilibrium, there could be a large amount of starting material remaining, resulting in a poor yield of the ester. In order to resolve this problem we make use of Le Chatelier's principle, which predicts that we can drive the equilibrium to the right (to the products) by having one of the reactants in excess (in effect, putting pressure on the left side). Usually, a threefold molar excess is enough to drive the equilibrium sufficiently to the right in an esterification reaction. Either the alcohol or the acid can be used in excess.
b.) Precisely. The Fischer esterification is done typically with an acid catalyst. You can add some drops of sulfuric acid, or saturate the solution with HCl gas.
When you work it up, a wash with a bicarbonate solution will neutralize any mineral acids you may have added in the reaction, and also remove any unreacted acid as its sodium salt.
Your ester is extracted into the organic phase. Everything else is left behind in the aqueous phase.
c.) so that there is no leakage. if connections are not tight product might be lost
d.) acetic acid is easy to remove due to its high solubility in water. it can simply be extracted into water.