[MaureenP]

Hi. I'm working on my General Chemistry lab report. I am second guessing my answer and would like some advice.
We were given this chart of solids and their melting points
Benzophenone  48C
p-Dichlorobenzene  54C
p-Dimethoxybenzene   59C
Biphenyl  71C
Durene 79C
Acetamide  82C

I was given an unknown solid of the above. I needed to find the melting point and identify the substance. My experiment showed a melting range of 79C-82.5C. I originally suspected Durene, but am second guessing now because it could be Acetamide....Can any one offer insight? Do I go by the temperature when it started to melt or by the one when it was completely melted?? Thanks!

[Arkcon]

You should go by when the sample began to melt.  If you're careful, and pick the smallest sample possible, consolidate it enough so that the mass of solid is together, but not so firmly that you can't see liquid forming, and you're quick enough at reading the temperature, you should get the correct answer.  But getting all of that down pat does take some practice.

You have to realize that there may be some error in your determination.  I think we can all accept that.  But what you have to now is try to consider -- are you likely a few degrees high, or low in your determination?  Try to consider -- it got to 80 C, then 81 C  and you still didn't see any melted sample?  Then you should know what its not, and narrow it down to what it is.

Look at this other thread on boiling point to see what I'm asking you to do.  http://www.chemicalforums.com/index.php?topic=78806.0

[MaureenP]

Thank you! I appreciate your feedback. It started melting at 79C and was completely melted by 82C. So if I go by the point it started to melt then it would be Durene exactly. I hope I interpreted your advice correctly.

[Arkcon]

Good work.