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Preserva Lab

Melting Point Apparatus

A melting point apparatus is a machine that helps determine and measure the melting point of a substance. Most elements and compounds have a specific temperature at which it melts. Small amounts of whatever is tested are inserted into small, thin tubes and inserted into the machine. A magnification tool is attached to the machine to closely observe the material in the tubes. The machine can then heat the tube and material at a predetermined temperature. The heat can be adjusted to find the temperature that the material just starts to melt, which is the melting point for that material.

A melting point apparatus can be shaped differently and is usually equipped with capillary tubes, a heating mechanism, and a magnifying apparatus. A capillary tube is a small, clear glass that is closed in one end to contain a sample being tested. The melting point of a substance is determined by visually looking at the sample and determining the melting point from when a solid turns into a liquid. Different substances have different melting points so if two substances look the same, say white and powdery, it doesn’t mean that that they are both the same substance. It is also used to test the purity of a product. An impure product melts at a lower temperature than a pure one. Therefore, you can easily tell if a substance is pure or impure by its identity and its point- if the substance being tested has a melting point at or below the predicted melting point.

Advantages:

Melting point analysis is a quick, relatively easy, and inexpensive preliminary analysis if the sample is already mostly pure and has a suspected identity. Additionally, analysis requires small samples only. Melting point analysis is fairly specific and accurate given its simplicity. Because a melting point is a unique physical characteristic of a substance, melting point analysis does have high specificity. Although, many substances have similar melting points, having an idea of possible chemicals in mind can greatly narrow down the choices. The thermometers used are also accurate.

Precautions:

As with any analysis, there are certain drawbacks to the melting point analysis. If the sample is not solid, melting point analysis cannot be done. Also, a melting point analysis is destructive of the sample. For qualitative identification analysis, there is now more specific and accurate analysis that exists, although they are typically much more expensive. Additionally, samples with more than one solute cannot be analysed quantitatively for purity. The biggest source of error stems from the visual detection of melting by the experimenter. Controlling the change rate and running multiple trials can lessen the degree of error introduced at this step.