CHM2210L Midterm Questions and Correct Verified Answers
0 view 0 purchase
Course
CHM2210L
Institution
CHM2210L
Do all mixtures of two different organic compounds exhibit a broad melting point
range?
No, eutectic mixtures(minimum mp for a mixture) melt with a sharp mp range.
Do organic compounds that exhibit polymorphism have different melting points?
Yes, variations in the intermolecular attraction o...
CHM2210L Midterm Questions and
Correct Verified Answers
Do all mixtures of two different organic compounds exhibit a broad melting point
range?
✓ No, eutectic mixtures(minimum mp for a mixture) melt with a sharp mp range.
Do organic compounds that exhibit polymorphism have different melting points?
✓ Yes, variations in the intermolecular attraction of different crystalline forms can
cause polymorphs to have different but sharp mp
What might you observe when an organic compound melts with decomposition?
✓ Darkening, change in color, effervesence
What characteristic in melting point behavior does an impure organic compound
usually exhibit?
✓ A broad and depressed mp range
Given that your unknown was one of those listed on page 1-8, if you obtained a
corrected melting point range of 68-70°C, could you definitely identify what your
unknown was?
Top Mark !!!
, Top Mark Questions and Correct Verified Answers
✓ According to the information, the unknown could either be benzhydrol,phenyl
benzoate, or biphenyl. After performing a mix-melting experiment than you
would be able to identify your unknown.
When should the start of the melt be recorded?*
✓ When the first appearance of liquid within the bulk of the sample is seen.
A compound is observed to melt sharply at 111°C with the vigorous evolution of a gas;
then the compound solidified and did not melt until 155°C sharply. Explain.
✓ Some organic compounds undergo 'elimination' reactions when heated, losing
such small molecules as H2O or CO2 and yielding other organic products. In this
case,
✓
✓ A → B + gas
✓ mp = 111d mp= 155
✓ d= decomposition
Suppose that your sample melts before you are ready to record the melting point.
Should you cool capillary and redetermine the melting point, or begin with a fresh
sample? Explain
✓ Start with a fresh sample; many organic compounds melt with at least some
decomposition- or when cooled, solidify in a different polymorphic form, and
thus would exhibit a different mp from that of the original sample.
Top Mark !!!
, Top Mark Questions and Correct Verified Answers
Why is it not good practice to mix two components by simply stirring them together
and then sampling them for a mixed melting point?
✓ Stirring two solid components together does not yield a homogenous mixture. A
small sample for a mp determination might thus be practically 100% of one
component.
Give a reason for using the technique.
A- The rate of heating is adjusted to no more than 4° per minute when the solid is
melting
B- The capillary tube is filled with no more than 2mm of sample.
C- The sample is firmly packed into the capillary tube.
✓ A-If the temperature is increased too rapidly at the melting point, the
thermometer, sample, and heating block will not be at thermal equilibrium, and
an erroneously depressed & wide mp range will be observed.
✓ B- Too much sample will take longer to melt and exhibit an erroneously large
and higher melting point range will be observed.
✓ C- A sample that is loosely packed, makes it difficult to determine when the start
of the melt begins.
A student accidently broke some pieces of glass which fell into the sample. The student
found that the melting point for that sample was 187-8. Is it necessary for the student
to take the melting point again?
Top Mark !!!
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller TopMarks1. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $13.49. You're not tied to anything after your purchase.
