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I was doing some practice problems when I came across this one enter image description here

The answer key says the answer is B but I don't know why. Isn't the difference in the molar masses of the two substances in D greater than that in B? Or am I supposed to look for how many times greater the molar mass of one is than the other? Thanks.

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The ability of liquid mixtures to separate is not based on density, but on polarity of each liquid. $\ce{CCl_4}$ and $\ce{C_6H_{14}}$ are both non-polar; they will mix well in solution and not separate easily. $\ce{CH_3OH}$ is polar due to presence of a polar alcohol group. Mixtures of non-polar and polar compounds will separate easily.

Density comes into play when you need to determine which of the compounds settle on top of the other. So, for (B), you would use the fact that the density of $\ce{CH_3OH}$ (0.79 g/mL) is less than $\ce{CCl_4}$ (1.59 g/mL) to say that the methanol layer would float on top of the $\ce{CCl_4}$ layer.

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  • $\begingroup$ Ah yes thank you. I don't know why I didn't think of that. Thanks a lot! :) $\endgroup$ – Clangorous Chimera Feb 27 '17 at 0:29

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