[burntbacon]

I took the local ACS exam and have 2 questions that are iffy.

What is the first thing that happens to I2 (iodine) solid when it is slowly heated at 1 atm? a. melts b. vaporizes c. changes color d. becomes atoms

2 organic compounds are mixed with melting points 112 and 114.  What is the new melting point?
a. under 112 b. 112 c. between 112 and 114 d. over 114

thanks

[Mitch]

2. The melting point is depressed, look up melting point depression.

[burntbacon]

I figured as much, but from what point is the melting point depressed?  My teacher says it should be either below 112 or at 112.  But I think the melting point is depressed from 114, thus putting it between 112 and 114.  What's correct?  

[hmx9123]

What was your answer for the first question, and why did you choose that answer?  I do have an opinion, but will wait until I hear from you.

[burntbacon]

Well, for the iodine question, I answered that it "vaporizes" thinking it means sublime.  But after researching on the internet, I found a phase diagram showing that Iodine melts at 1 atm at about 113 C.  However, many places I look say that iodine sublimes at room temperature.  I guess the strict definition of vaporize is to go from liquid to gas...

I'm confused and I do not know what the answer is for 1.  

For 2, does Raoult's law only apply to solutions not pure liquids?  Just to make it easier, I put the melting points at 0 and -2 C.  The 0 has a higher melting point which will raise the melting point of the -2.  So the answer should be between 0 and -2.  Can I get a verification of the answer of 2, if the new melting point is between 112 and 114?

[Demotivator]

First off, nice name. Try reducing the cooking time!  

If the two substances were liquids, which they aren't, Raoult's law would limit the boiling points of any mixture  to between the bps of the pure substances.
However, this question deals with melting. Also, this question seems to be an example of a badly phrased one that cannot be answered because one needs to know additional information such as the actual composition of the mixture.
Refer to figure 3 of the link to illustrate.
http://www-ec.njit.edu/~grow/phasedigram/BiphaseDig.html

[burntbacon]

The composition, I seem to recall, is equal concentrations of each.

[Demotivator]

It's still a lousy question. In practical terms, 114 and 112 are very close to each other so that it is highly likely that the melting point of equal mixture will be less than the low one of 112 ( like figure 3).
Strictly speaking, components with  different melt pts can look like figure 2, where an equal mixture can lead to a melt pt in between.

[AWK]

Iodine sublimes (vaporizes) below melitng point (113-114 C) and boils at 183 C (then vapor pressure will reach 1 atm)

Under 112

[burntbacon]

I just found out I got first in my school and 4th in the region with a 55/60!  I'll be going to the national ACS exam in April.    Anyone have any tips? I'll probably have more questions later when I start studying for it.

Thanks for all the replies.

[Demotivator]

Please don't become a chef!  

[Mitch]

Congratulations!