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Which of these substances is more soluble in $\ce{CCl4}$?

  • $\ce{CH3F}$
  • $\ce{I2}$
  • $\ce{Na2SO4}$
  • $\ce{HCl}$

How do I even solve this kind of exercise?

My guess is that $\ce{CCl4}$ is non-polar. Therefore the substance we're gonna need must be non-polar as well. The only non-polar substance is $\ce{I2}$ so that should be the answer.

Is my reasoning fine and, more importantly, is there another way to solve this kind of problem? What if they give me two options that are non-polar?

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You are correct in your assumption. For these types of problems it is usually safe to assume like dissolves like and choose the answer with the most similarity in terms of intermolecular bonding. For a general description you can check here.

When you get into questions with two options that have similar intermolecular forces it gets a little hairy. For example, I think a question like, "which is more soluble in carbon tetrachloride: n-Pentane or n-Hexane?" would be fairly challenging to answer without experimental or computational data to compare.

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  • $\begingroup$ Why, that one is easy: pentane and hexane both would be infinitely miscible with $\ce{CCl4}$. You are right in general, but this example would look better with two solid compounds. Say, naphthalene and $\ce{I2}$. Which is more soluble? I don't know. $\endgroup$ – Ivan Neretin Oct 6 '15 at 9:55
  • $\begingroup$ That's a great point Ivan, I was grasping for examples, I should have chosen some higher order solid n-alkanes. A relevant paper: for anyone interested pubs.acs.org/doi/abs/10.1021/ie00063a008 $\endgroup$ – Aaron Oct 7 '15 at 2:42
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If this is your introduction to chemistry answer is I2. It gets more complicated in extreme conditions such as ultrahigh pressure or temperature.

I would stick with I2 (nonpolar-nonpolar)

for degrees of polarity check molecular structure, electron orbitals etc. this and other similar online tools helps too: http://www.gregthatcher.com/Chemistry/ChemicalBondPolarityCalculator.aspx

a lesson on interactions between non-polar molecules:

http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Atomic_and_Molecular_Properties/Intermolecular_Forces/Overview_of_Intermolecular_Forces/Interactions_Between_Nonpolar_Molecules

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