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Physical Properties Dimethyl ether vs ethanol

  • Thread starter trollcast
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  • #1
trollcast
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Homework Statement


Explain the difference in the following properties of dimethyl ether and ethanol:

1) Solubility in water
2) Rate of evaporation

Homework Equations


The Attempt at a Solution



1) Due to the oxygen being bonded to 2 carbon atoms none of the hydrogen atoms in the dimethyl ether molcule have a dipole. This means that diethyl ether cannot form hydrogen bonds with the water molecules, this means the dimethyl ether is immiscible with water.

In ethanol the oxygen atom is bonded to a hydrogen which gives it a dipole, this allows the ethanol molecule to form hydrogen bonds with the water molecules and therefore it is miscible with water.

2) As noted above dimethyl ether cannot from hydrogen bonds. This means that the only intermolecular forces are Van der Waal's forces. These are weaker than the hydrogen bonds that can form between ethanol molecules. As both molecules have the same RFM this would imply that diethyl ether will boil at a lower temperature and therefore evaporate more quickly at a given temperature compared to ethanol.



I just wanted to check if my answers made sense and if I had used the right words in places.
 

Answers and Replies

  • #2
epenguin
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Homework Statement


Explain the difference in the following properties of dimethyl ether and ethanol:

1) Solubility in water
2) Rate of evaporation

Homework Equations


The Attempt at a Solution



1) Due to the oxygen being bonded to 2 carbon atoms none of the hydrogen atoms in the dimethyl ether molcule have a dipole. This means that diethyl ether cannot form hydrogen bonds with the water molecules, this means the dimethyl ether is immiscible with water.

In ethanol the oxygen atom is bonded to a hydrogen which gives it a dipole, this allows the ethanol molecule to form hydrogen bonds with the water molecules and therefore it is miscible with water.

2) As noted above dimethyl ether cannot from hydrogen bonds. This means that the only intermolecular forces are Van der Waal's forces. These are weaker than the hydrogen bonds that can form between ethanol molecules. As both molecules have the same RFM this would imply that diethyl ether will boil at a lower temperature and therefore evaporate more quickly at a given temperature compared to ethanol.



I just wanted to check if my answers made sense and if I had used the right words in places.
It makes sense.

Only one extra detail: ether is not totally immiscible with water. In fact depending on how it is made most ether will contain a little water. Dry ether will absorb water from the atmosphere unless prevented.

If you add water to ether or vice versa they mix till the ether is about 7%, then they separate into two layers; the ether layer contains some water and the water layer some ether.

So you have to think there is still some dipolar interaction between water molecules and the O of the ether.
 

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