The reason for the experiment was used to determine the purity of a known substa
ID: 595324 • Letter: T
Question
The reason for the experiment was used to determine the purity of a known substance. We were given a pure sample of an unknown from the following list:
Compound Melting point (celsius)
Acetylsalicylic acid 138-140
Benzoic acid 121-122
Benzoin 135-136
Dibenzoyl ethylene 108-111
Succinimide 122-124
Toluic acid 108-110
The goal was to determine the identity of the unknown using the melting point technique. If all of the compounds in the list had distinctly different melting points, it would be possible to determine the identity of the unknown by just taking its melting point. However, each of the compounds in this list has a melting point that is close to the melting point of another compound in the list. therefore, the melting point of the unknown will allow you to narrow down the choices to two compounds. To determine the identity of yout compounds, you must perform mixture melting points. A mixture melting point that is depressed and has a wide range indicates that the two compounds in the mixture are different.
Our unkown B had a melting point of 123-129 celsius.
We used Benzoin and Benzoic acid because they were farely close to the range of our unknonw.
Benzoin was 105-115 when we used the melting process
Benzoic acid was 122-129 celsius when we used the melting process
BOTH started at 100 celsius when we started the melting process
We concluded that our unknown was Benzoic acid acid from the results.
I need helping answering the following questions from the picture:
Explanation / Answer
Chemical compounds have a wide range of solubilities in distilled water and water containing acids or bases. The solubility can be tested by adding a small amount of solid sample to a small amount of solvent in a test tube and stirring. If solid remains then we would say the substance is insoluble or only slightly soluble in that solvent. Note in the list of chemicals attached, substances such as calcium carbonate are examples of these insoluble substances. If a substance dissolves, then it can't be calcium carbonate (or some other insoluble substance) and these can be eliminated from the list of possible compounds. The reverse also applies. That is, if the substance doesn't dissolve, then it can't be one of the soluble compounds.
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