Скачать или смотреть [Orgo Lab 2] Melting-Point Apparatus

Today, we will take a look at how to measure the melting point range of a solid.

The melting point is the temperature at which the solid and liquid phases of a pure substance coexist at the pressure of one atmosphere. The melting point of a solid is used by organic chemists to identify a compound, and also to ascertain its purity.

The Capillary Method is one technique to determine the melting point range. This method operates by placing a solid sample at the bottom of a capillary tube, then slowly heating the tube and recording the melting point range of the investigated sample.

To get an accurate melting point range, you have to heat the sample at an extremely slow rate, at around 1 to 2 degrees Celsius per minute. The slower the better. However, some solids have high melting points that it will take forever for the sample to melt. To solve this, we have something called plateau temperature. A plateau temperature is generally set at 5 to 10 degrees Celsius below the expected melting point.

So what can you do with this? You can heat the material quickly to the plateau temperature, which will substantially reduce the waiting time. Then at the plateau temperature, you can heat up at a significantly slower rate, at around 1 to 2 degrees Celsius per minute, to obtain an accurate reading of the melting point range.

Our lab uses the Stuart apparatus to measure a sample’s melting point range. Here, we will show you the steps of taking the melting point range of a known sample using this apparatus.

Video Production: Dr. Xu's Research Group (Dr. Xu, Han, Emma, Nhu, and Emily).

Contents:

0:00 - Introduction
0:10 - Melting Point Range of a Solid
1:07 - The Capillary Method
1:39 - Plateau Temperature
2:30 - Melting-Point Apparatus
2:42 - Step 1: Pack the Sample
4:28 - Step 2: Set the Plateau
5:25 - Step 3: Heat Up Slowly
5:53 - Step 4: Record MP Range
7:20 - Special Case: New Compound