S99 - page 1 pts NAME:_ Chemistry 231L/232L MID-TERM 4/7...

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page 1 —— pts NAME:__________________________ Chemistry 231L/232L MID-TERM 4/7 Spring 1999 Assistant Professor: D. D. Gergens, Ph. D. GIVE BRIEF ANSWERS TO THE FOLLOWING QUESTIONS 1. (2) At what rate should a sample be heated in order to find an accurate melting point? ___________. 2. (4) True / False T F If the rate of heating of the oil in your Thiele tube in a melting-point determination is too high, the melting point that results will likely be too low. T F A eutectic mixture has a sharp melting point, just like a pure compound 3. (4) Predict the affect of the following impurity on the melting point of your unknown. a) If your sample was contaminated with small amounts of broken glass. The melting point of your compound would be ( too high, too low, remain unchanged ). Explain. 4. (3) If you are given two solids with the SAME MELTING POINT of 50 °C, how could you determine easily whether the two samples were the same substance or different substances? 5. (3) A student uses the Thiele micro melting-point technique to determine the melting point of an unknown and reported it to be 100 °C. Is this value believable? Explain why or why not. 6. (2) Contact lenses: A. may be worn in the lab when splash-proof goggles are used.
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S99 - page 1 pts NAME:_ Chemistry 231L/232L MID-TERM 4/7...

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