posted by .

Question: An unknown compound gave a melting point of 230C. When the molten liquid solidified, the melting point was redetermined and found to be 131C. Give a possible explanation for this discrepancy.

My answer: The compound sublimed.

How would sublimation work to do this?

Doesn't sublimation send it right from melting point to boiling point? So when they heated it to melting, they didn't catch it until it hit boiling point. Then they solidified it and got the temp as soon as it got liquid.


When a substance sublimes, it goes from the solid state directly to the vapor state without going through the liquid state. And it will solidify from the vapor sate directly to the solid state without passing through the liquid state. So there is no boiling point. The literature will quote a sublimation temperature.

How about if it was in a capillary tube? That might not explain why it was so high initially.

Maybe the thermometer was broken. Any hints?


The only thing that comes to mind is that it melted at 230 C, rearranged into another compound, cooled and solidified. The new pure comound melted at the lower temperature.

Thanks very much. I had so much Organic work this weekend that I couldn't believe it but I think I'm finished for the night.


Could it form after melting into the solid of another isomer? Often isomers have vastly different mp...
as an example, the para, ortho, and meta forms of dichlorobenzene come to mind.

Sounds like that is the answer.

Thanks from Sheryl

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. ORG. CHEM- Extraction Conclusion

    Does this sound okay, if not how might i improve it?
  2. chem

    1.) When determining the melting point it's described in my text as recording 2 points in the melting process. a) when the first drop of liquid is seen b) when all of the compound is liquified and since I have to determine the melting …
  3. chemistry

    Which of the following describes the compound Mn(NO2)2?
  4. Chemistry

    Student in O-Chem Lab conducts a melting point experiment with an unknown compound and observes a melting range of 210 – 218C. Is this a typical range for a melting point?
  5. chemistry

    Some properties of the two compounds are listed below: Melting point- Compound X= -114*C Compound Y= -138*C Boiling Point- Compound X= 78*C Compound Y= -22*C Net Dipole?
  6. Organic Chemistry - Melting Point

    You have an unknown with an observed melting point of 90-93°C. Is your unknown compound A with a reported melting point of 95.5-96°C or compound B with a reported melting point of 90.5-91°C?
  7. Chemistry

    you were asked to determine the melting point of an unknown compound in order to identify at as one of the compounds you had previously examined. What else could you have done to make sure that your unknown was indeed the compound …
  8. organic chemistry

    A sample of Compound X is analyzed and found to have a melting point range of 110-120 °C. Would you try to purify it further to get a sharper melting point?
  9. Organic Chemistry

    Why is the melting point of a known compound (ex. acetanilide) determined before the melting point of the unknown compound?
  10. Organic chemistry

    An unknown compound (x) melts at 60°C and is mixed with a compound (y) that melts at 45°C and is soluble in x. Will the Melting point for the mixture start below 45°?

More Similar Questions