5. (a) Use the vapor pressure graph for ethanol (curve 2) in the graph below. If

Question

5. (a) Use the vapor pressure graph for ethanol (curve 2) in the graph below. If a rotavapor is used at 40 C what is the pressure that you must operate it to remove ethanol from a wine (ethanol -water mixture with flavors and colors). (b) Use the P vs T graph for water to estimate the pressure required in a pressure cooker to cook carrots at 110 C. (c) Is it possible to achieve such pressures naturally on the earth? 101,3 kPa 1 atm 760 mmHg kPa 10 75 1 50 25 34,6 C 78,3°C 100°C 20406080 100 Vapor pressure of ether (1), ethanol (2) and water (3) as a function of temperature. 60 50 30 20 00110 120 130 140 150 160 Temperature C'C) P vs T for water

Explanation / Answer

a. Boiling temperatures (temperature at which liquids become vapor) of liquids can be reduced by reducing pressure. Rotavapor works on this principle. It can be used to remove solvents by evaporation. In rotavapor, the pressure is decreased to reduce boiling temperature. Operating rotavapor at 40 C means that the solvent has to evaporate at 40 C. The solvent here is water.

From the graph, water evaporates at 40 C when the pressure is 10 kPa. Since there are impurities such as flavors and colors which generally increase the boiling temperature, the pressure required would be slightly above 10 kPa (0.099 atm)

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b. The pressure vs temperature (P vs T) graph shown in the figure shows that water boils at different temperatures at different pressures.

Using the graph, it is clear that water boils at 100 C when pressure is 1 atm. Each square box along Y-axis represents 0.2 atm change in pressure. The pressure at 110 C is 1.0+0.4 = 1.4 atm.

Hence, the pressure required in the pressure cooker to cook carrots at 110 C is 1.4 atm.

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c. Pressures higher than 1.4 atm can be seen inside earth's core. Since there is more matter pressing down on the core of the earth, the pressures and temperatures are very high. The pressure in core is around 3300000 atm.

High pressures can also be seen in deep sea. The pressure increases by 1 atm for every 33 feet below sea level. At about 100 feet, the pressure will be as high as 4 atm.

Pressures higher than 1.4 atm can be achieved naturally on earth.

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