1、Compiled by Vlad Ladziata 6/14/20181Chapter 3: Melting points and Boiling pointsMelting PointsA. Calibration of the thermometer using naphthalene (80-82C)B. Take the melting point of pure urea and cinnamic acidC. Take the melting point of pure urea - cinnamic acid mixture. There are three mixtures (
2、1:3, 1:1, 3:1), one group only need to do one. D. Take the melting point of unknowns, and all the candidates are listed on page 54. Part 1 Calibrate the melting point apparatus using naphthalene (pp. 49-51)To take the melting point you need make two readings:1. when the substance begins to melt (fir
3、st liquid drops are observed)2. when the substance completely melts (the last trace of solid melts)Thus, melting point is a temperature range e.g. 165-166oCYou will calibrate the melting point apparatus using naphthalene (melting point 80-82oC). The difference between the values found and those expe
4、cted (80-82oC) constitute the corrections that must be applied to future temperature readings.1. Using a metal spatula, get a small amount of naphthalene on a watch glass, crush the sample to a fine powder.2. Push a melting point capillary into the powder; force the powder down in the capillary by t
5、aping the capillary. Make sure that the column of solid in the capillary is no more than 2-3 mm in height and should be tightly packed.3. Put the capillary into the melting point apparatus, turn it on. If the approximate melting temperature is known, the melting point apparatus can be heated rapidly
6、 until the temperature is about 20C below this point. During the last 15-20C, make the temperature rise slowly, so that the rate of heating at the melting point is no more than 1C per minute while the sample is melting.4. Watch the melting of sample carefully, read and record both the temperature wh
7、en the substance begins to melt and the temperature when the substance is completely melted.Part 2 Determine the melting points of pure urea (m.p. 132.5-133C) and cinnamic acid (m.p. 132-133C) (starts on p. 52)1. Take a small amount of pure urea and cinnamic acid respectively, follow the steps of Pa
8、rt 1, and determine the melting points of pure urea and cinnamic acid.Part 3 Determine the melting points of urea-cinnamic acid mixtures (starts on p. 53).1. There are three mixtures of urea and cinnamic acid in the approximate proportions 1:3, 1:1, and 3:1. Each group will only need to do one. TA w
9、ill assign this to you.2. Follow steps of Part 1 to determine the melting point of the assigned mixture.Part 4 Determine the melting points of unknowns (Starts on p. 53).1. Each group will be assigned an unknown.2. Prepare two capillaries with unknown sample. Follow steps 1-4 of Part 1, make a fast
10、determination to ascertain the approximate melting point (fast heating rate) and then cool Compiled by Vlad Ladziata 6/14/20182the melting point apparatus below the roughly determined melting point (approx. 5-10oC lower) and make a slow, careful determination using the other capillary and applying 1
11、C per minute heating rate.3. After you got the melting point, look to the Fig. below (and table on p. 54) and find the compound with the corresponding melting point. Put the unknown # and the answer in your lab notebook.Part 2 Boiling PointsA. You will need to calibrate the thermometer. This procedu
12、re is found on page 55. The details are as follows:1. Test the 0 C point of the thermometer: Put the thermometer in an ice/distilled water bath, and read the thermometer when it is constant and no longer changing.2. Test the 100 C point of the thermometer: Put 2 ml of distilled water in the test tub
13、e with a boiling chip3. Boil the liquid over a sand bath with the thermometer tip above the liquid and in the vapor from the boiling liquid. See figure 3.13 on page 58. NOTE: The thermometer must be above the liquid. Read the temperature value when it is constant and no longer rising.B. Take the boiling point of 95% ethanol (78 C). 1. Take 2 ml 95% ethanol into the test tube with a boiling chip.2. Follow A step 3.Answer questions 5, 6, 7, 13 (pp. 59-60)
