If the boiling point of methoxymethane is 248K, predict the boiling point of ethanol.

351K

The correct answer is option 3. 351K.

The boiling point of a substance is determined by the strength of the intermolecular forces present. Stronger intermolecular forces result in a higher boiling point because more energy (in the form of heat) is required to overcome these forces and convert the substance from a liquid to a gas.

Methoxymethane (Dimethyl Ether, \(CH_3OCH_3\))

Boiling Point: 248 K

Intermolecular Forces:

Dipole-Dipole Interactions: Methoxymethane is a polar molecule due to the difference in electronegativity between carbon and oxygen, creating a dipole moment.

London Dispersion Forces: Present in all molecules, these are weak intermolecular forces due to temporary dipoles

Lack of Hydrogen Bonding: Methoxymethane does not have an -OH group, which is necessary for hydrogen bonding.

Ethanol \((C_2H_5OH)\)

Intermolecular Forces:

Dipole-Dipole Interactions: Ethanol is also a polar molecule due to the presence of the \(-OH\) group.

London Dispersion Forces: Present in ethanol as well.

Hydrogen Bonding: Ethanol can form hydrogen bonds because of the -OH group. Hydrogen bonding occurs when hydrogen is bonded to a highly electronegative atom (oxygen in this case), and it can interact strongly with lone pairs of electrons on oxygen atoms of neighboring molecules.

Impact of Hydrogen Bonding

Hydrogen bonding is a particularly strong type of dipole-dipole interaction. Molecules capable of hydrogen bonding generally have much higher boiling points than those that cannot form hydrogen bonds, assuming similar molecular weights and structures.

Boiling Point Comparison

Given that methoxymethane has a boiling point of 248 K and it cannot form hydrogen bonds, while ethanol can form hydrogen bonds:

The presence of hydrogen bonds in ethanol greatly increases its boiling point compared to methoxymethane.

In fact, the actual boiling point of ethanol is about 78.37 °C, which is 351.52 K \((\approx 351 K )\).

Therefore, the boiling point of ethanol is best predicted to be around: 351 K.