Prelab Assignment Experiment 4 Answers
1. Calculate the molecular weights of isopentyl alcohol and isopentyl acetate.
88 and 130 g mol-1 respectively.
2. In the preparation of isopentyl acetate concentrated sulfuric acid is added to the reaction
mixture. What purpose does the acid serve in the reaction?
There are two: firstly, as stated in the introduction to the experiment, the acid acts as a
catalyst, increasing the reaction rate. A less important purpose is related to the strong
affinity that concentrated sulfuric acid has for water. The presence of H2SO4 helps to remove
water (a product of the reaction) from the mixture and thus drive the reaction to the right
(in accord with Le Chatelier’s Principle). The amount of added acid is small though, so this
effect is of only minor importance.
3. Why must the separatory funnel be frequently vented when washing the reaction mixture
with aqueous sodium carbonate?
Not only is one of the reactants an acid, but further acid is added to the reaction mixture as
a catalyst. Consequently we expect that the final mixture will be strongly acidic. The sodium
bicarbonate is added to react with, and thereby remove, this acid. Bicarbonates react with
acids, releasing carbon dioxide. If the funnel is not frequently vented, the build-up of carbon
dioxide within could – in principle – cause the funnel to explode. More probably, the stopper
will be blown off, or liquid thrown out when the tap is opened. Thus, frequent venting of the
gas is essential. (You can see the effect of the acid when the sodium bicarbonate solution is
added; there is usually a vigorous, though not dangerous, initial evolution of bubbles; this
dies down as the acid is used up.)