Solving General Chemistry Homework: Determining Substance Identity & Thermocline

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Discussion Overview

The discussion revolves around a general chemistry homework problem that includes two main questions: determining the identity of a pure substance based on its density and explaining the phenomenon of temperature variation in a lake, specifically the concept of thermocline. The scope includes theoretical understanding and conceptual clarification in chemistry.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant asserts that the identity of a pure substance can be determined based solely on its density, claiming that all pure substances have unique densities.
  • Another participant counters this by mentioning that optical isomers can have identical densities, suggesting that density alone may not be sufficient for identification.
  • Concerns are raised about the precision of density measurements and the vast number of substances that could potentially have similar densities, questioning the reliability of density as a sole identifier.
  • Regarding the thermocline, one participant agrees with the term but is challenged by another who clarifies that thermocline refers to a layer where temperature changes abruptly, implying a need for deeper understanding of water density behavior.
  • One participant suggests that the complexity of thermocline may exceed what is typically covered in a general chemistry class, indicating a potential gap in the curriculum.

Areas of Agreement / Disagreement

Participants express differing views on the sufficiency of density for identifying pure substances and the explanation of thermocline, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

Limitations include assumptions about the precision of density measurements and the definitions of terms like thermocline, which may not be fully addressed within the context of a general chemistry course.

Who May Find This Useful

This discussion may be useful for students in general chemistry courses, particularly those grappling with concepts of density and temperature stratification in fluids.

SDanyal
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Homework Statement


a) In general, can we determine the identity of a pure substance based only on its density?
b) During the summer the temperature of water is warmer at the surface of a lake than in depth. Disregarding the fact that the lake is heated by the sun light, explain this phenomenon.

Homework Equations


None


The Attempt at a Solution


a) Yes because all pure substances have their own density. Density for all pure substances is different.
b) I believe that this phenomenon is called Thermocline.


I'm not sure if these answers are correct, if anyone can shine some light, it would be great. It's my first day in college, and I'm having trouble. Thanks :D.
 
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For the density, it seems reasonable to argue both ways, since one could always bring up the argument of pure water freezing to ice, which floats on pure liquid water since the density is less. I personally found both arguments when I used a search engine on this problem, since I was interested.
 
SDanyal said:
Density for all pure substances is different.

Not necesarilly, optical isomers have crystals of idetical densities, yet they are different substances. Even assuming densities are different, question is - are we able to measure density precisely enough? Assuming you have measured density with +/- 1mg/mL accuracy (high one!) and assuming all substances we know have densities in the range 0-22.61, that gives place for 22610 substances. Not much.

I believe that this phenomenon is called Thermocline.

No, thermocline is a surface at which temperature of the water (or air) changes abruptly.

Think in terms of densities. What will happen to warm water immersed in the lake of cold water? To cold water in the lake of warm one? Remember they won't mix fast.
 
Last edited:
1) Nope.

2) Consider the fact that the bottom of the ocean is dark while the top of the ocean is light.
 
Oh. Disregarding the fact that the lake is heated by the sunlight.

If this is a general chemistry class, quite frankly, a chemistry class is not going to explain thermocline; it's more complicated than a chemistry class can explain.
 

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