I was comparing boiling points of $\ce{CHCl_3}$ and $\ce{CH_3Cl}$. According to me B.P. of $\ce{CHCl_3}$ should be higher due to it's higher molecular mass than $\ce{CH_3Cl}$, but the answer is opposite ,ie. B.P. of $\ce{CH_3Cl}$ $\gt$ B.P. of $\ce{CHCl_3}$.Why?
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asked Feb 3, 2014 at 5:01
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2 Answers
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Molecular mass has NO pertinence to BP, water and ammonia. Look up the BP of perfluorocyclohexane, hexafluorobenzene, and the hydrocarbons. If I want to volatize iron, ferrocene. If I want to volatize iron more, $\ce{Fe(hfac)_3}$ where the ligand is the bidentate enolate anion of 1,1,1,5,5,5-hexafluoro-2,4-pentanedione. Big MW. What are the MW and BP of $\ce{UF_6}$? $\ce{-Si(CH3)_3}$ also confers volatility.
Boiling points are more about polarizability, intermolecular van der Waals and such. Bigger molecules are overall electronically floppy. Benzene, toluene, xylenes – nice BP steps, but not because of MW. Look up $\ce{SF_6}$ bp. $\ce{I(CF3)_7}$ boils near 0 °C. Calculate that MW, and its vapor’s mass/liter at STP compared to dry air at 29 g/liter.
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Edit: Your argumentation is valid, there was probably just some confusion in the notes.
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but the answer is opposite ,ie. B.P. of $\ce{CH3Cl}$ > B.P. of $\ce{CHCl3}$.
Really?
$\ce{CH3Cl}$ has a boiling point of −24 °C. It is a gas.
$\ce{CHCl3}$ has a boiling point around 61 °C.
Edit: Your argumentation is valid, there was probably just some confusion in the notes.
answered Feb 3, 2014 at 5:46