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

  1. 👍 0
  2. 👎 0
  3. 👁 871

Respond to this Question

First Name

Your Response

Similar Questions

  1. Chemistry

    An unknown compound contains only C, H, and O. Combustion of 4.50 g of this compound produced 10.2 g of CO2 and 4.19 g of H2O. What is this empirical formula of the unknown compound?

  2. Same substances?

    Question: Two substances, A and B, have the same melting point. how can you determine if they are the same without using any form of spectroscopy? Explain in detail. My answer: Perform a mixture melting point. In this procedure,

  3. chemistry

    If a compound is a brittle, blue crystal with a high melting point, what type of compound is it?

  4. organic chemistry

    2. An unknown white solid has melting point range 119 – 121o C. Benzoic acid is a white solid of 122 o C melting point. How can a student confirm the identity of the unknown solid (is the benzoic acid or not)

  1. Mixed melting point

    Question: A compound melting at 134 degrees C was suspected to be either aspirin (mp 135C) or urea (mp 133C) Explain how you could determine whether one of these two suspected compounds was identical to the unknown compound

  2. Chemistry

    An Ap student got a lab report back with "-4.5 % error" written in red on it. He had found the boiling point of an unknown liquid to be 45 C. What is the correct boiling point of his unknown liquid? I know first I would write -4.5

  3. 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? Explain.

  4. Phase diagram

    Question: A solid substance has a vapor pressure of 800 mm Hg at its melting point (80 degrees C). Describe how the solid behaves as temperature is raised from room temperature to 80 C while the atmospheric pressure is held

  1. Chemistry

    After a Melting point determination, why can't you re-use the solidified substance and capllary tube for subsequent determination?

  2. chemistry

    Here is the question: A sample of an unknown volatile liquid was injected into a Dumas flask (mflask=27.0928g. Vflask=.104L) and heated until no visible traces of the liquid could be found. The flask and its contents were then

  3. organic chem

    An unknown compound melted at 131-133°C. It is thought to be one of the following compounds(mp,°C): trans-cinnamic acid (133-134); benzamide(128-130); DL-malic acid(131-133); or benzoin(135-137). The mixture melting points of

  4. Chemistry

    Imagine that you have a pure sample of an unknown compound that you are told is either 2-naphthol OR benzoic acid. In the lab, you also have access to samples of pure 2- naphthol and pure benzoic acid. However, both of these pure

You can view more similar questions or ask a new question.