2. The melting point of pure benzoic acid and pure naphthol are 122.5°C and 123°C
respectively. You are given a pure sample that is known to be either pure benzoic acid
or 2- naphthol. Describe a procedure you will use to determine the identity of the
sample.
To determine the identity of the sample, which can either be pure benzoic acid or 2-naphthol, you can perform a melting point test. Here's the procedure you can follow:
1. Set up a melting point apparatus: Start by setting up a melting point apparatus, which typically consists of a heating device, such as a Mel-Temp apparatus, a capillary tube, and a thermometer.
2. Prepare the capillary tube: Take a thin-walled capillary tube and insert a small amount of the unknown sample into it using a clean spatula or a weighing boat. Ensure that you use a tiny amount, as a larger sample may lead to inaccurate results.
3. Run a control test: The next step is to run a control test using a known pure sample of either benzoic acid or 2-naphthol. Insert a small amount of the known pure sample into a separate capillary tube. This will serve as a reference point for the expected melting point of the compound.
4. Obtain the melting point range: Insert both the unknown sample and the known sample into the melting point apparatus. Gradually increase the temperature using the heating device. Observe the appearance of the sample as it is heated and note the temperature range at which it starts to melt and completely liquefies. This range is known as the melting point range.
5. Compare the melting points: Once you have obtained the melting point range for the unknown sample, compare it with the melting points of pure benzoic acid (122.5°C) and pure naphthol (123°C). If the melting point of the unknown sample matches closely with the melting point of either benzoic acid or naphthol, it is likely that the unknown sample is that compound.
6. Perform a mixed melting point test (if necessary): In case the unknown sample does not perfectly match the melting point of either benzoic acid or naphthol, you may need to perform a mixed melting point test. Mix a small amount of the unknown sample with an equal amount of the suspected compound (either benzoic acid or naphthol) and repeat the melting point test. If the mixed melting point is depressed or wider, it suggests that the unknown sample is different from the suspected compound.
By following this procedure, you can determine the identity of the unknown sample based on its melting point and comparing it with the known melting points of pure benzoic acid and pure naphthol.