# Of the given the following solvents, which should give rise to the greatest vapour pressure at laboratory temperature?

## $\text{A. Water;}$ $\text{B. ethanol;}$ $\text{C. glycerine;}$ $\text{D. Methanol.}$

Nov 19, 2017

$\text{Option D}$

#### Explanation:

Here we use volatility as an indicator of intermolecular force. The higher the intermolecular force the GREATER the boiling point, and the LOWER the volatility.

We gots water, whose normal boiling point you know, ethanol, which boils at $78$ ""^@C, methanol, which boils at $64.7$ ""^@C, and glycerine, $H O {H}_{2} C - C H \left(O H\right) C {H}_{2} O H$, whose boiling point would be mucho elevated due to intermolecular hydrogen bonding....$290$ ""^@C (I just looked it up)....

And thus methanol should have a HIGHER vapour pressure than the rest of the molecules.....and should be lower than NONE of them.

Good question, I am stealing it.

Note that while both methanol and ethanol participate in intermolecular hydrogen bonding, ethanol is a a heavier molecule, and the carbon chain allows another intermolecular force to contribute, i.e. the dispersion force, which increases in magnitude with the length of the carbon chain. $\text{n-propanol}$ has a boiling point of $97.5$ ""^@C. $\text{n-butanol}$ has a boiling point of $117.7$ ""^@C.