We are asked to explain why propyl alcohol has a higher boiling point than isopropyl alcohol. To explain this, we have to do the following steps.
Step 1: Evaluate the intermolecular force present.
The boiling point increases with increasing intermolecular force: London dispersion force < dipole-dipole < hydrogen bonding < ion-dipole.
Step 2: Examine the size of the molecules with the same intermolecular force
Bigger molecules have a higher surface area and thus have a higher boiling point.
Step 3: Examine the branching of molecules of the same size
Linear molecules pack more densely than branched molecules and thus have a higher boiling point.
Propyl alcohol (CH3CH2CH2OH) and isopropyl alcohol [(CH3)2CHOH], whose space-filling models are shown, have boiling points of 97.2 oC and 82.5 oC, respectively.
Explain why the boiling point of propyl alcohol is higher, even though both have the molecular formula of C3H8O.
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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.
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Based on our data, we think this problem is relevant for Professor Albright's class at UMICH.