CHMA2000 EXPT 1 -melting point - Dr. Hoyle

1 CHMA2000 expt 1: melting points Experimental Objectives: At the end of this experiment you should be able to: 1. Measure a melting point 2. Understand the reason for performing a mixed mp determination 3. Determine the purity of an organic compound using mp 4. Identify organic compounds using mp Prelab Exercises: Before coming to lab you should: 1. Read about mp determinations and the experiment and its background. 2. Prepare a flow chart outlining the lab exercises. 3. Research the mp and structures, and construct a table for all possible compounds to be used (include this in your formal lab report). Part A: USE OF A melting point APPARATUS Procedure: The melting point apparatus, has an electrically heated aluminum block fitted with a thermometer reading to 300oC.

2 The sample is either placed between two 18 mm microscope cover glasses or in a capillary tube, which are placed on or in the aluminum block (depending on which apparatus you use). The temperature is regulated by means of a variable transformer, and the sample temperature is observed with the aid of a magnifying glass. You only need to use a very small amount of sample in your measurements. You are provided with a small quantity of an unknown solid. Determine its melting point ; you may need to perform a rough determination first. Now, consider the compounds in Table 1. Which group is your unknown from? Perform a mixed melting point determination as follows. Place a small amount (end of a spatula) of your unknown and an equal amount of one of the substances from the identified group on a watch glass and carefully grind the two together with a glass rod.

3 Determine the melting point . Repeat this procedure with the other substance in the group. Record your results and draw some scientific conclusions. Table 1: Data for possible unknown compounds for Experiment 1B Group Approx mp (oC) Compound name Chemical structure Actual mp (oC) 1 55 Diphenylamine p-Dichlorobenzene 2 70 Biphenyl Stearic acid 3 100 Malic acid o-Anisic acid 4 120 Benzoic acid Phenyl sulfone 5 135 Mannose Malonic acid 6 175 Thiourea Tartaric Acid Part B: MIXED melting points AND IMPURITIES Procedure: In this part of the experiment you will work in small groups (as assigned by the lab instructor).

4 Within your group you are required to measure the following: 1. melting point range of pure phenyl sulfone 2. melting point range of pure benzoic acid 3. melting point ranges of the mixtures of phenyl sulfone and benzoic acid provided to your group. Plot a graph of melting point range (y-axis) versus composition (in percent) from 0-100% benzoic acid. Please note that there are two y-axes in such a graph, one at 0% and one at 100%. (It is not possible to have values of composition outside this range!) Attach the graph to your formal lab report in the results section Safety for Experiment 1: REMEMBER, IF YOU ARE NOT SURE ABOUT ANYTHING ASK BEFORE YOU START WORK IN THE LAB EYE PROTECTION MUST BE WORN AT ALL TIMES IN CHMA2000 LABS Use of a melting point Apparatus When using the melting point apparatus please remember that these instruments will get hot.

5 Care must be taken not to burn yourself. When handling the unknown compounds be sure that if any is spilled that it is cleaned up immediately. Also if the unknown compound makes contact with the skin ensure that the exposed area is flushed immediately with water. DISPOSAL Cover slips or capillary tubes containing samples, when removed from the melting point apparatus, should be placed in the appropriate garbage can - marked "broken glassware only". If extra unknown or known are left after you have completed your melting point determinations place the extra in the beaker on the front bench. Please do not place the extra in the garbage, down the sink, or back in the container which it came from. The MSDS numbers above refer to Material Safety Data Sheets which are available for review please ask Ms.

6 Tate or Mr. Fergus for access to these sheets. ALL ACCIDENTS MUST BE REPORTED TO LAB INSTRUCTOR. Last updated May, 2016 Copyright J. Hoyle & M. Tate, 2016