have a organic chem question.

[James3shin]

Pure solid x has a melting point of 125 C, and pure solid y has a melting point of 250 C. What happens to the melting point of solid x if 1% of solid Y is added?

I'm pretty sure that the melting point of the new solid will go up, but is there any way to calculate the new melting point of the new solid? My math instincts are saying "no" but I just want to make sure.

Any help is appreciated. thanks

 

[Howard]

If 1% of solid Y is added? So is the final distribution 99% X and 1% Y? Or is 1% of the volume you have of X added as Y?

 

[Howard]

Anyway, there's no way to be sure what the melting point is, unless you assume that the melting point of the alloy increases linearly as a function of % volume of Y.

 

[James3shin]

99% of X and 1% of Y

 

[Howard]

Assuming that:

Originally posted by: Howard
the melting point of the alloy increases linearly as a function of % volume of Y.

Then 0.99(125) + 0.01(250) = new temp.

 

[James3shin]

hmm that does make sense howard, thanks man!

 

[Googer]

Originally posted by: Howard
Assuming that:

Originally posted by: Howard
the melting point of the alloy increases linearly as a function of % volume of Y.

Then 0.99(125) + 0.01(250) = new temp.

Google Calculator

The answer is 126°, to me that does not sound correct. I think your Order of Operations are out of wack.

 

[Howard]

Originally posted by: Googer

Originally posted by: Howard
Assuming that:

Originally posted by: Howard
the melting point of the alloy increases linearly as a function of % volume of Y.

Then 0.99(125) + 0.01(250) = new temp.

Google Calculator

The answer is 126°, to me that does not sound correct. I think your Order of Operations are out of wack.

Why doesn't it make sense? You are only adding a little bit of something with a higher melting poitn.

 

[James3shin]

well you start with a block of pure solid x that has a 125 C melting point. If you fortify it with a new solid, in this case "y", that has a boiling point of 250 C, then the new overall solid should follow what howard say...i guess, sounds right to me.

 

[Googer]

Originally posted by: Howard

Originally posted by: Googer

Originally posted by: Howard
Assuming that:

Originally posted by: Howard
the melting point of the alloy increases linearly as a function of % volume of Y.

Then 0.99(125) + 0.01(250) = new temp.

Google Calculator

The answer is 126°, to me that does not sound correct. I think your Order of Operations are out of wack.

Why doesn't it make sense? You are only adding a little bit of something with a higher melting poitn.

I stand corrected, I mis-read the opening post. I believe you are correct.

 

[TNM93]

If both X and Y are heterogenous, they'd continue to have the same melting points. If not, I would assume you'd have to convert percentages into mass, then go from mass into stoichiometry, etc. Been a long time since I've been in Chem.

 

[liluqt]

Hi.

 

[miniMUNCH]

In reality, it depends whether solid Y would increase or decrease the cohesive forces of X (X-X interaction).

If I had to make a judgement call, I'd say adding 1% of pure solid Y to otherwise pure solid X would most likely slightly depress the melting point of X as "premelting" would occur at slightly lower temperatures localized around sites where Y is present on the surface.

It partly depends upon what X and Y are...and really depends upon whether X is a crystalline solid or an amorphous solid. If X is crystalline...then replacing X in a periodic crystalline lattice every so often with Y would raise the lattice energy of structure and thus decrease the energy required for melting...so melting would happen at a lower temperature. If X is an amorphous solid then I'd say it is a "case by case" thing.

 

[YJK76]

Originally posted by: miniMUNCH
In reality, it depends whether solid Y would increase or decrease the cohesive forces of X (X-X interaction).

If I had to make a judgement call, I'd say adding 1% of pure solid Y to otherwise pure solid X would most likely slightly depress the melting point of X as "premelting" would occur at slightly lower temperatures localized around sites where Y is present on the surface.

It partly depends upon what X and Y are...and really depends upon whether X is a crystalline solid or an amorphous solid. If X is crystalline...then replacing X in a periodic crystalline lattice every so often with Y would raise the lattice energy of structure and thus decrease the energy required for melting...so melting would happen at a lower temperature. If X is an amorphous solid then I'd say it is a "case by case" thing.

yea, what miniMUNCH said.
not all melting points are linear therefore you can't assume or "extrapolate" unless you know exactly what the composition of both X and Y are and how their chemical make-ups dictate their melting point behaviors.