Identification of an Unknown Solid by Melting Point

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¥°. Summary of Results
A. Melting point of Benzoic Acid
Temperature (¡ÆC)Observation
UnmeltedWhite salt
First liquid appear point122Grainy and shiny white
Becoming all liquid125Clear
B. Melting point of unknown #42
1st trial
Temperature (¡ÆC)Observation
UnmeltedShiny light yellow crystal
First liquid appear point99Grainy yellow
Becoming all liquid101Clear
2nd trial
Temperature (¡ÆC)Observation
UnmeltedShiny light yellow crystal
First liquid appear point95Grainy yellow
Becoming all liquid97Clear
C. Melting point of mixture (Unknown + Benzil)
Temperature (¡ÆC)Observation
UnmeltedShiny light yellow crystal
First liquid appear point95Grainy yellow
Becoming all liquid97Clear
¥±. Discussion of results
Assessment of sample purity for a known substance. By comparing observed range for an actual sample to the known range for a pure sample, I can tell whether my actual sample is pure or contaminated (the range is depressed and broadened). So, In part A, melting point of benzoic acid was observed in range 122 to 125 ¨¬C. By comparing melting point of benzoic acid (121 ¨¬C) with result from part A, the result is little higher than the pure melting point. So I can tell it is little contaminated. Identification of an unknown sample (compare its observed melting range with known compounds). Unknown #42 was found to have a melting range of 99 to 101 ¨¬C in 1st trial and 95 to 97 ¨¬C in 2nd trial. The only one given pure compounds with similar melting ranges was benzil (94~95 ¨¬C). The mixture of the unknown and benzil produced a mixture that melted at 95~97 ¨¬C. The benzil mixture had a melting point similar to both pure benzil and the unknown. This indicates that unknown ¡°42¡± is benzil. However, by comparing melting point of pure benzil (94~95 ¨¬C) with result from part B(95~97 ¨¬C), the result is little higher than the pure melting point. So I can tell my unknown is a little impure. And I found the problem in the...
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