Sep 1, 2016 - Course Description: Surveys foundational concepts of lifespan development psychology, such as sensitive periods, developmental stages and transitions, and trajectories of change across the lifespan. Text: Berger, K.S., & Chuang, S.S. (2
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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.)