A level Chemistry Comparing boiling points of molecules

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Bence9912
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Say you were given a 6 mark question where it asked you to put in order, from lowest to highest boiling point an alkane, alcohol and an ester, giving verbal justification for your answer.

Has anyone got any tips for answering questions like this and how you would know which one has the highest boiling point with reasoning.
The CGP a level chemistry book does not go into any detail with types of questions like this and how to answer them.

thanks
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Mystakes
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(Original post by Bence9912)
Say you were given a 6 mark question where it asked you to put in order, from lowest to highest boiling point an alkane, alcohol and an ester, giving verbal justification for your answer.

Has anyone got any tips for answering questions like this and how you would know which one has the highest boiling point with reasoning.
The CGP a level chemistry book does not go into any detail with types of questions like this and how to answer them.

thanks
I haven't covered esters yet but for alcohols and alkanes, the boiling point of alkanes is lower because the only intermolecular force involved is van der waals forces, whereas alcohols also have hydrogen bonding between the lone pair on the oxygen, and hydrogen. Boiling point is always to do with intermolecular forces as far as I know, but I'm not 100% sure.
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Bence9912
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(Original post by Mystakes)
I haven't covered esters yet but for alcohols and alkanes, the boiling point of alkanes is lower because the only intermolecular force involved is van der waals forces, whereas alcohols also have hydrogen bonding between the lone pair on the oxygen, and hydrogen. Boiling point is always to do with intermolecular forces as far as I know, but I'm not 100% sure.
i believe then its similar with ester which would probably also have van der waals forces between them,longer the chain length the greater the strength of van der waals forces. However i am not sure if hydrogen bonds can form between the esters O in the C=O bond and an a hydrogen on another ester due to double bond. But on the other hand oxygen would still have a lone pair making it possible to form hydrogen bonds. Can someone clarify that?
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username2752874
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(Original post by Bence9912)
i believe then its similar with ester which would probably also have van der waals forces between them,longer the chain length the greater the strength of van der waals forces. However i am not sure if hydrogen bonds can form between the esters O in the C=O bond and an a hydrogen on another ester due to double bond. But on the other hand oxygen would still have a lone pair making it possible to form hydrogen bonds. Can someone clarify that?
There is no hydrogen bonding between typical esters. They have a higher boiling point than alkanes because they contain the polar COO group, so it contains a permanent dipole - permanent dipole forces, which is stronger than the induced dipole - induced dipole forces of alkanes. The more polar something is, the stronger it's VDWs forces.
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Bence9912
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(Original post by GradeA*UnderA)
There is no hydrogen bonding between typical esters. They have a higher boiling point than alkanes because they contain the polar COO group, so it contains a permanent dipole - permanent dipole forces, which is stronger than the induced dipole - induced dipole forces of alkanes. The more polar something is, the stronger it's VDWs forces.
which is caused by the deprotonation of the carboxylic group causing the charge on the oxygen with the C-O^- to be delozalized between two oxygen's?making it more stable?

so would ester have highest boiling point?
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username2752874
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(Original post by Bence9912)
which is caused by the deprotonation of the carboxylic group causing the charge on the oxygen with the C-O^- to be delozalized between two oxygen's?making it more stable?

so would ester have highest boiling point?
Higher than alkane, lower than alcohol

Generally speaking though, the size of the molecule matters too. Decane has a higher bp than methyl methanoate
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Bence9912
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(Original post by GradeA*UnderA)
Higher than alkane, lower than alcohol

Generally speaking though, the size of the molecule matters too. Decane has a higher bp than methyl methanoate
Great Thanks
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