CH 337 – Winter 2015
Lab report #1
The Purity and Purification of Solid Melting Points.
The melting point method is used to find the melting range to determine the purity of biphenyl, naphthalene, and mixture compound of this two compound. With the same method, the unknown compound will be determined base on the melting range. According the giving data, the unknown D is Succinic Acid, which has melting point at 1880C, because the unknown has the closet melting range from 1810C to 2010C.
Introduction: Each compound has specific melting range. Melting Point method is used to establish that range to find the purity. The melting point has initial state, when the solid state starts to change likes color, form, shape, etc; and final state, when the solid state turns to liquid completely. The purity of products can be determined by looking at the melting range. In the pure compound, the melting range changes sharply between the initial melt to the final melt, generally less than 1 - 2 0C. However, the impurity compound will have much wider range of melting point. Some compound has very similar melting point. The melting point depression method will be used to help to identify the unknown solid compound. First step is to establish a melting range of the unknown mixture. Next, a new mixture is a combination of the unknown with the know-mixture, which has the closest melting to the unknown melting range. By using mel-temp machine, the new mixture will be tested for melting point. The final result will be compared with the know mixture.
Experiment: The process of the experiment was performed according the lab manual and the instruction was giving the teacher assistant. The procedure started with a filling about 2cm of the mixture into the capillaries tube. The mixture was pulverized and loaded into a standard closed-end of the tube. The capillaries was inserted into the Mel-Temp device and heated up gradually. The initial point and the final point will be recorded according the state of the mixture. Each type of mixture was tested twice. The final data was recorded by taking the average for the two trails. Part A: Each student was requires finding the melting range of the pure naphthalene and biphenyl separately. Also, each group was assigned with specific mixture of 90% naphthalene-10% biphenyl, 70% naphthalene-30% biphenyl, 50% naphthalene-50% biphenyl, 30% naphthalene-70% biphenyl, or 10% naphthalene- 90% biphenyl. Finally, the collecting data was shared from other group. The data would be used to create a graph and calculate the eutectic point.
The percent mole formula:
% Mole of N = x 100 Mole of N (naphthalene) = Mole of B (biphenyl)= Part B: With the same steps, the data of melting range on the unknown A was collected. First, the melting point a small sample of the unknown solid was recorded. The results was compared with the melting point of the know compounds. An equally mixture , by mass, of unknown A and a know compounds, which has the similar melting range, was determined by using the mel-temp. The initial and final melting points were recorded.
Result: Part A: Mixture
Trail 2 initial final
Initial final 100% B
10% N 90% B
30% N 70% B
50% N 50% B
70% N 30% B
90% N 10% B
Figure 1: Melting point diagram of Napthalene and Bipheny
Average MP-range (0C)
Initial final Compound D
50% unknown A 50% succinic acid
Discussion: Part A: The range…