Quiz Bank 6a

# Quiz Bank 6a - Quiz Ideas for 6A TAs Experiment 1 Melting...

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Quiz Ideas for 6A TA’s Experiment 1 Melting Point 1. List several sources of experimental (not human) error when a melting point is determined by a capillary-tube technique. Suggest how these errors might be avoided. 2. What are some possible complications to the use of mixed melting points for checking the identity of compounds with the same melting point? 3. Briefly define each of the following terms: (a) eutectic temperature, (b) eutectic composition, (c) melting point, (d) boiling point, (e) density, (f) refractive index 4. How would it be possible to differentiate between two substances if they have the same melting point without the use of spectroscopy? 5. What are the necessary steps needed to determine the melting point of a substance that sublimes before it melts? 6. A compound melting at 134 o C was suspected to be either aspirin (mp = 135 o C) or urea (mp = 133 o C). How would it be possible to determine which of the two suspected compounds was the unknown? 7. An unknown compound gave a melting point of 230 o C. When the molten liquid solidified, the melting point was re-determined and found to be 131 o C. Explain. Density 1. What is the formula to calculate density? 2. How is density affected when adding a solid compound to a pure liquid? 3. Why is the temperature also recorded when a density measurement is determined? 4. When a density for a liquid is expressed in the following way: (Benzene) 8787 . 0 15 4 = d g/mL What does the “15” represent? How about the “4”? Refractive Index 1. nD 20 is often how refractive indices are labeled and reported. What does the “20” stand for? 2. Why is it not possible to have a nD 20 to be <1? Experiment 2

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Distillation 1. Define or describe the following terms: (a) boiling point, (b) partial vapor pressure, (c) theoretical plate/efficiency, (d) through-put, (e) reflux ratio, (f) column hold-up, (g) HETP, (h) Raoult’s Law, (i) ideal solution 2. Concerning the benzene/toluene temperature vs. composition graph on page 9 of the 6a lab manual, what would be the new approximate composition if an 80:20 mixture of benzene/toluene were to go through 4 theoretical plates? 3. Under what conditions can a good separation be achieved when performing only a simple distillation? 4. Where should the thermometer bulb be placed in a distillation apparatus?
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