posted by Christine .
student perform 2 melting point determinations on a crystalline product. In one determination, the tube contained a sample 1 - 2 mm in height, and the melting point was 141 - 142 ¢ªC. In the second determination, the sample hight was 4 - 5 mm and the melting range was 141 - 145 ¢ªC. Explain what may have caused the broader range in the second determination. (The actual melting point is reported to be 143 ¢ªC.)
This is my reasoning but I don't know if it is correct. The broader melting range is observed in the second one because the sample of the height was greater.
You are correct; however, your prof won't give you any credit for that (at least I wouldn't). Example: Why is grass green? Answer: because the sun is shining. (I wouldn't get any credit for that either. You see what I mean. (The sun shining lets there be enough light that I can see the green color BUT it doesn't answer why grass is green in the first place.) So what is the real reason why the melting point range was increased. Because the oil bath in which the melting point tube was immersed had temperature fluctuations from the bottom of the tube to the top of the tube. If you had two thermometers, one located at the lower end of the tube and the other at the top of the tube you would have been able to see the difference in the temperature of the two places. Check my thinking. (I'm assuming an oil bath was used.)