Melting+Points

=Melting Points=

__Introduction__
The purpose of this lab is to obtain the knowledge of how to use a MelTemp apparatus properly and efficiently. Melting point data of different substances such as 1-indanone and 3,4-dimethoxybenzaldehyde will be collected throughout the experiment. In addition, melting points containing different ratios of a mixture between cinnamic acid and urea will be observed to determine a relationship between melting points of pure substances and that of mixtures. This is a very important part of the lab experience. 1-indanone and 3,4-dimethoxybenzaldehyde will be compounded together to show this relationship as well; however, these two substances will also be combined with sodium hydroxide to make a completely new substance of which, melting point data will be collected.

__Procedure__
Measure the melting point of one of (?) 1-indanone. Repeat the melting point determination 3 times, each time allowing a different person in your group to watch the melting occur. Record your results on the chalkboard at the front of the room. Weigh out 0.20 g 1-indanone and 0.25 g 3,4-dimethoxybenzaldehyde. Take the chemicals back to your working area for later use. **In large group discussion** we will talk about **precision** in melting point data, and we will make predictions about what might happen to melting points when two substances (such as the two we are considering) are mixed together. After the class predictions have been listed, place the two substances in the bottom of a small beaker. Crush and mix them thoroughly, using a glass stir rod or the back of a spatula. Complete mixing may take several minutes. Record any relevant observations. What do you observe? What do you think has happened? What has happened to the melting point? Add approximately 0.05 g (which is just about the size of the head of a pin) of powdered NaOH to the beaker and mix thoroughly for about 5 minutes. Allow the mixture to stand for an additional 10 minutes. Add about 2 mL of 10% HCl to the beaker. Test the pH of the resultant mixture by dipping the end of a glass rod into the mix and then touching it to a piece of pH paper. If the solution is not acidic, add 1 mL HCl and test again. Collect the solid product by vacuum filtration, using the aspirator to draw liquid through the filter. Dry the solid in a drying oven for 15 minutes, then test the melting point of the dry substance. Obtain a 1:1 mixture and a 5:1 mixture of urea and cinnamic acid and test melting points. Record these melting points in the data.

"YouTube." //Melting Point Determination//. Web. 09 Oct 2010. []

__Data__
1- indanone: Range ||
 * Run ||  Sweating Temp.  || Melting
 * 1 ||  39.8⁰C  ||  40.3⁰C -41.2⁰C  ||
 * 2 ||  39.8⁰C  ||  40.3⁰C -41.2⁰C  ||
 * 3 ||  39.0⁰C  ||  40.6⁰C-41.4⁰C  ||

Melting range of 1-indanone + 3,4-dimethoxybenzaldehyde product: 159.4 ⁰C – 160.6 ⁰C Including data from the larger group would be helpful, even if it is simply the averages from the other groups.

Pure urea melting range: 134.5 ⁰C - 136.1⁰C Urea + Cinnamic Acid Melting Range (1:1): 102.3 ⁰C – 103.5⁰C (1:5): 101.2 ⁰C – 108.4⁰C

__Analysis__
The accepted melting range for 1-indanone is 38.0 ⁰C -42.0 ⁰C which indicates that the observed melting ranges were correct. Adding an impurity to a pure substance such as cinnamic acid + urea lowers the melting point of the substance. The more impurity that is present, the lower the melting point and the broader the range. I am sure you can tell me more about this! Your other data (the indanone and dimethoxybenzaldehyde part) isnot discussed here.

__Conclusion__
It is important for chemist to understand the effects that are caused by impurities in a substance. This lab highlights the fact that impurities added to a pure substance will lower its melting range and that the melting range of a substance indicates the purity of the substance. more more more! discuss error. fill out your discussion. you have not included the post-lab question.