Practice problems for Prelim 2, Fall 2007 1. You are working in a lab and you see a sealed 1 liter flask sitting on the lab bench. There is some liquid in the bottom of the flask. You recall that you boiled some liquid in that flask, driving off all air in the vapor space above the liquid. Then, you sealed the flask tight and let it cool to the lab temperature (30°C). However, you cannot recall whether it was ethanol or ethyl acetate that you boiled, and you forgot to label the flask (which is a serious violation of EPA rules!) Fortunately, the flask is fitted with a pressure gauge that reads 120 mm Hg. a) Write down a calculation that shows whether the material in the flask is ethanol or ethyl acetate. Explain your reasoning and state assumptions. b) You estimate there is 10 ml of liquid in the flask. What is the total massin the flask?
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