Basic question on recrystallization.

  • Thread starter Thread starter scorpion990
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around the phenomenon of melting point changes observed in a solid before and after recrystallization. Participants explore potential explanations for why a solid that initially melts at 150-160 degrees Celsius exhibits a lower melting point of 145-145.5 degrees Celsius after recrystallization, considering factors such as purity, impurities, and eutectic compositions.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested, Homework-related

Main Points Raised

  • One participant suggests that the observed drop in melting point could be due to impurities, although they note the narrow melting point range of the recrystallized solid suggests high purity.
  • Another participant proposes that the recrystallization might have resulted in a eutectic mixture, which could explain the sharp melting point.
  • A different viewpoint raises the possibility that the initial melting point measurement was affected by rapid heating, leading to an inaccurate observation of the melting point.
  • One participant speculates that the original composition may have been altered during recrystallization, bringing it closer to a eutectic composition.
  • It is clarified by one participant that the scenario presented is hypothetical and intended for a lab assignment rather than based on real data.

Areas of Agreement / Disagreement

Participants express various hypotheses regarding the observed melting point changes, with no consensus reached on a single explanation. Multiple competing views remain regarding the causes of the melting point drop.

Contextual Notes

Participants note the potential influence of impurities and measurement techniques, but the discussion does not resolve the underlying assumptions or dependencies related to the observations.

Who May Find This Useful

This discussion may be useful for students or individuals interested in the concepts of recrystallization, melting point determination, and the effects of composition on phase transitions.

scorpion990
Messages
86
Reaction score
0
I have a quick question:
Suppose that you observed a solid melting at 150 degrees - 160 degrees Celsius. Once it is recrystallized, the observed melting point drops to 145-145.5 degrees Celsius. How can this be?

At first, I thought it was due to an impurity, which would act to lower the melting point. However, the melting point of the recrystallized solid is very narrow, so it is probably quite pure. Then again, the recrystallized mixture might be eutectic, which would explain the sharp melting point. But then again... How is it possible to contaminate a sample that badly?

Any help is appreciated.
 
Physics news on Phys.org
Reaction with solvent?
 
Perhaps during the measurement of the first melting point, the sample was heated too quickly so that melting wasn't observed until the chamber was at a temperature higher than the real melting point.
 
scorpion990 said:
I have a quick question:
Suppose that you observed a solid melting at 150 degrees - 160 degrees Celsius. Once it is recrystallized, the observed melting point drops to 145-145.5 degrees Celsius. How can this be?

At first, I thought it was due to an impurity, which would act to lower the melting point. However, the melting point of the recrystallized solid is very narrow, so it is probably quite pure. Then again, the recrystallized mixture might be eutectic, which would explain the sharp melting point. But then again... How is it possible to contaminate a sample that badly?

Any help is appreciated.

I'm not an expert on this topic however your last assumption is probably correct , you have have simply altered the original composition so that the mixture is closer to the eutectic composition. What are you working with?
 
It's not real data. Rather, it's just a question I have to answer and attach to my lab.
 

Similar threads

Undergrad Melting point of graphite and diamond?
  • · Replies 3 ·
Replies
3
Views
6K
Is My Compound Pure Despite Low Percent Recovery?
  • · Replies 2 ·
Replies
2
Views
4K
Chemistry- Basic Energy Transfer Questions
  • · Replies 3 ·
Replies
3
Views
2K
How Do You Purify Compounds Using Recrystallization Techniques?
  • · Replies 4 ·
Replies
4
Views
23K
Question on entropy in adiabatic phase change
  • · Replies 8 ·
Replies
8
Views
3K
Undergrad Any stable amorphous substances?
  • · Replies 3 ·
Replies
3
Views
3K
High School Question about the term "frozen"
  • · Replies 6 ·
Replies
6
Views
8K
Mixed Melting Point of Two Pure Solid Crystals
  • · Replies 7 ·
Replies
7
Views
5K
Graduate Could meteorites contain evidence of troilite drainage and trapped iron grains?
  • · Replies 6 ·
Replies
6
Views
4K
Why Did the Aspirin Melting Point Decrease in This Experiment?
  • · Replies 1 ·
Replies
1
Views
10K