Why is the melting point of a known compound (ex. acetanilide) determined before the melting point of the unknown compound?

I think it is to determine if the unknown is a pure substance but I am not sure..I just need to be pointed in the right direction.

You can tell if the unknown is a pure substance by the melting point range (or lack of a range). I suspect it is to determine if the thermometer is calibrated properly.

You are correct, determining the melting point of a known compound before the melting point of an unknown compound serves the purpose of verifying if the unknown compound is a pure substance. Melting point determination is an important technique in organic chemistry for characterizing and identifying compounds.

To understand why the melting point of a known compound is measured first, let's delve into the principle behind melting point determination. The melting point is the temperature at which a solid substance changes from its solid state to a liquid state at atmospheric pressure. It is a unique physical property of a compound and can serve as a characteristic identifier.

When measuring the melting point of an unknown compound, we aim to compare it with the melting point of similar known compounds. If the unknown compound has a similar melting point to a known pure compound, we can infer that the unknown compound is likely to be the same substance or a compound with similar properties.

To ensure the accuracy of this comparison, we first determine the melting point of a known compound. This known compound acts as a reference or a control sample. By measuring the melting point of the known compound, we establish a reliable reference range for expected melting points.

Then, when we measure the melting point of the unknown compound, we can compare it with the known compound's melting point range. If the unknown compound's melting point falls within this range, it suggests that the unknown compound is likely to be a pure substance or a compound with similar properties.

If the assumed pure known compound has a different melting point, it could indicate that the known compound is impure, or there might be other factors affecting the melting point measurement.

In summary, measuring the melting point of a known compound first before the unknown compound helps establish a reference range and provides a basis for comparison in determining the purity of the unknown compound.