Problem: Ethylene glycol (HOCH2CH2OH) and pentane (C5H12) are both liquids at room temperature and room pressure, and have about the same molecular weight.One of these liquids has a much lower normal boiling point (36.1 oC) compared to the other one (198 oC). Which liquid has the lower normal boiling point?

FREE Expert Solution

We are asked which between ethylene glycol (HOCH2CH2OH) and pentane (C5H12) have a lower normal boiling point.


Recall that there are several types of intermolecular forces, IMF, (in decreasing strength):

1. Ion-dipole interaction – occurs between an ion and a polar covalent compound; strongest IMF

2. Hydrogen bonding – occurs in compounds where hydrogen is directly connected to an electronegative element such as N, O, or F; 2nd strongest IMF

3. Dipole-dipole interaction – occurs between two polar covalent compounds; 3rd strongest IMF

4. Dispersion forces – occurs in all compounds and is the primary IMF exhibited by nonpolar compounds; weakest IMF


Compounds with strong intermolecular forces have high boiling points. This is because they require more energy to be able to break the bonds during the phase transition.


So, we need to identify which among the given compounds has the weakest intermolecular forces.


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Problem Details

Ethylene glycol (HOCH2CH2OH) and pentane (C5H12) are both liquids at room temperature and room pressure, and have about the same molecular weight.

One of these liquids has a much lower normal boiling point (36.1 oC) compared to the other one (198 oC). Which liquid has the lower normal boiling point?

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What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Intermolecular Forces and Physical Properties concept. If you need more Intermolecular Forces and Physical Properties practice, you can also practice Intermolecular Forces and Physical Properties practice problems.