Melting Point determination- Acetanilide, Benzoic Acid and Salicylic Acid

July12,2014

1. MELTING POINT DETERMINATION EXPERIMENT#8 Diaz, hovelyn lou Martinez, ma. czarina Esteban, reynan james SANOTA, MARIELA Gregorio, krystal jane

2. INTRODUCTION A melting point can be used to identify a substance and to get an indication of its purity. The melting point of a solid is the temperature at which the solid  exists in equilibrium  with its liquid state under an external pressure of one atmosphere. Both the melting point range (the interval between the beginning of liquefaction and complete liquefaction) and the temperature of complete liquefaction are valuable indicators of the purity of the solid compound. A pure crystalline organic compound usually possesses a  sharp  melting point and it melts completely over a narrow temperature range.

3. PROCEDURE Prepare 3 melting point capillary tubes by heating the middle portion of the capillary tube (1mm diameter) and when soft enough, pull in opposite directions to completely seal and separate the two. Test the tube if completely sealed by blowing air on the open end, and feeling with fingers if air comes out from the sealed end, it should be heated further to completely seal it.

4. PROCEDURE Introduce powdered samples of acetanilide, benzoic acid and salicylic acid into 3 separate prepared capillary by putting a small amount of sample (about 3-4 mm diameter) on a piece of clean dry paper and pushing the open end of the capillary tube into the sample to scoop it up. The column of solid should not be more than 1cm, in the tube length and it should be tightly packed.

5. PROCEDURE Prepare the set-up for melting point determination

6. PROCEDURE Fasten the capillary tube containing acetanilide to the thermometer with string or a rubber bond so that the sample is close to and on a level with the center bulb of the thermometer bulb. Attach the thermometer in its place in the set-up where its bulb and the capillary tube (with sample) is centered in the beaker and submerged in the oil.

7. PROCEDURE Heat the oil bath with a moderate flame. Then gradually increase the size of the flame so as to cause a rise in temperature of 1  or 2 per minute. Stir the bath continuously to have a uniform heating.

8. PROCEDURE RECORD: The temperature at which melting begins and The temperature when the entire 1cm powdered sample in the capillary tube is completely melted Repeat the same procedure by using benzoic and salicylic acid

9. DATA AND RESULTS COMPOUND INITIAL TEMPERATURE FINAL TEMPERATURE ACETANILIDE 105 C 114 C BENZOIC ACID 110 C 122 C SALICYLIC ACID 140 C 150 C

10. COMPOUND MELTING POINT ACETANILIDE 114.3 °C BENZOIC ACID 121-123°C SALICYLIC ACID 159°C

11. QUESTIONS 1. What are the bonding forces that hold together the molecules in a crystal? Give examples of compounds with such types of bonding forces. I ntermolecular forces hold its molecules together such as Van der Waals forces, Ionic bonding, Covalent bonding, H ydrogen bonding and M etallic forces . Examples: I2, P8 and solid SO2 = V an der Waals forces. W eakly held and easily broken with low melting points NaCl , MgO , CaCo = I onic forces composed of the electrostatic attractions of anions and cations . H ard , brittle poor electrical conductors. SiO = Covalent bonded crystal forming quartz and diamond crystals . Hard, poor conductors of heat and electricity and have high melting points All of the metallic elements: Ag, Mg, Fe Cu, etc = Metallic bonding positive ions surrounded by delocalized valance electrons . Conduct heat and electricity well, have low to high melting points and can be soft or hard.

12. QUESTIONS 2. What is the effect of an impurity on the melting point of a substance? They cause the melting point to turn from the standard. It actually makes the magnitude of the melting point lower because impurities decreases the quality of a material. The melting point is not anymore sharp, but a range of values. The more impurities present, the greater the range of values.

13. QUESTIONS 3. How can melting point be used in identifying and/or characterizing unknown compounds? Compounds are identified because each compound have different melting points. The melting point value can then be matched to a table of melting points to identify the unknown.

14. APPLICATION Melting points of organic solids are useful to organic chemists because: They (and other physical constants) aid in the recognition of such compounds. Extensive tables have been compiled, giving the melting points of different compounds and their derivatives. They aid in obtaining information about the purity of an organic compound. A pure organic compound has a "sharp" melting point. They are useful in establishing the identity of a solid compound: Mixed Melting Point Determination . This technique is based on the fact, that one substance will lower the melting point of another substance if mixed with it. A "mixture" of two specimens of the identical material, by contrast, shows no change in melting point.

15. GENERALIZATION By performing this experiment, we learned that the more carbon a chemical or compound have, the higher the melting point. Salicylic acid got the highest melting point among the three because e lectrostatic bonds between the constituents of molecules of salicylic acid are increasing over time through a series of additions of heat than those between acetanilide and benzoic acid. It needs more heat or energy to melt. Melting Point tells us that it is something about the forces that hold the molecules together, and the fact that some substances are not molecules at all, but networks of atoms held in place by either ionic or covalent bonds. It is the formation of a network of interconnected atoms that makes for the high melting point, not the type of bonding between the atoms. 

16. GENERALIZATION It is those compounds which do not form networks that have lower melting points, because weaker Van der Waals forces are the only forces keep the molecules together.