[GabrielOPerez]

Hey guys! I have a pre-lab due, and I'm having a few questions that aren't explicitly stated by my lab manual.

1.)
Why is it good practice to perform a mixed melting point determination at two different ratios of unknown to known materials in the melting point capillary?

A.) Because it is possible that one particular combination of materials generates a eutectic.
B.) In case one of the materials in the mixture sublimes.
C.) Because inconsistencies in the finely divided powder will alter the melting point.

My answer would be A, but I'm not certain. I would like to think that a sharp melting range would be a call for another measurement.

2.)
Which of the following statements about melting point determination are true? Select all that apply.
[?] The melting point is a physical measure of the forces holding the material into its crystal lattice.
This is the heat of fusion, not the melting point, correct?
[X] The lower limit of the melting temperature range occurs when the first crystal starts to melt.
That one's true.
[?] The literature value of melting point is often quoted as only the lower limit.
No mention by my lab manual, but I'm fairly sure this is false based off the fact that the lower limit is unpredictable.
[X] The upper limit of the melting temperature range occurs when the last remaining crystal melts.
This should be true.

3.) List the procedural steps, from start to finish, that are required to perform an accurate melting point determination.
(Several items are present, and we have to sort them into the correct order.)
 
I have the image attached of what I believe to be the proper procedure; however, I feel as if the language used is ambiguous.

[Arkcon]

Hey guys! I have a pre-lab due, and I'm having a few questions that aren't explicitly stated by my lab manual.

1.)
Why is it good practice to perform a mixed melting point determination at two different ratios of unknown to known materials in the melting point capillary?

A.) Because it is possible that one particular combination of materials generates a eutectic.
B.) In case one of the materials in the mixture sublimes.
C.) Because inconsistencies in the finely divided powder will alter the melting point.

My answer would be A, but I'm not certain. I would like to think that a sharp melting range would be a call for another measurement.

When you're faced with a question like this, and you want to determine the bestest possible, lose zero points at all, defeat all tricks, answer -- what you should do is look up the definitions of each possible word in the question.  Do you know the definitions of eutectic and sublime?  If this is were essay question, you'd be expected to write a paragraph including all points.  If this is a multiple guess question, then .. pretend its an essay, and write one in your head (or on paper) in case its an essay on the exam.

[trinitrotoluene]

Hey guys! I have a pre-lab due, and I'm having a few questions that aren't explicitly stated by my lab manual.

1.)
Why is it good practice to perform a mixed melting point determination at two different ratios of unknown to known materials in the melting point capillary?

A.) Because it is possible that one particular combination of materials generates a eutectic.
B.) In case one of the materials in the mixture sublimes.
C.) Because inconsistencies in the finely divided powder will alter the melting point.

My answer would be A, but I'm not certain. I would like to think that a sharp melting range would be a call for another measurement.

2.)
Which of the following statements about melting point determination are true? Select all that apply.
[?] The melting point is a physical measure of the forces holding the material into its crystal lattice.
This is the heat of fusion, not the melting point, correct?
[X] The lower limit of the melting temperature range occurs when the first crystal starts to melt.
That one's true.
[?] The literature value of melting point is often quoted as only the lower limit.
No mention by my lab manual, but I'm fairly sure this is false based off the fact that the lower limit is unpredictable.
[X] The upper limit of the melting temperature range occurs when the last remaining crystal melts.
This should be true.

3.) List the procedural steps, from start to finish, that are required to perform an accurate melting point determination.
(Several items are present, and we have to sort them into the correct order.)
 
I have the image attached of what I believe to be the proper procedure; however, I feel as if the language used is ambiguous.

I'm not sure the order that you have the items from the image in is correct. It is kind of like doing a titration, where you do a gross one first (drop solution ~1 mL at a time), to get a
"rough" idea where the equivalence point is. Then try again adding drop by drop when you get near the approximate equivalence point to get a more exact number...  Hopefully that makes some sense.


hint hint: your gross trial melted ~150degrees, theres no sense in letting it cool all the way back to RT before adding another sample.

Good luck