Ethanol as a Solvent

[velox]

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Here's an exam question which im not too sure on:

Account for ethanol's extensive use as a solvent for non polar and polar substances. Use a diagram to explain your answer. (2marks)

Could someone give a sample answer? Thanks.

[Dreamerish*~]

Originally Posted by velox

Here's an exam question which im not too sure on:

Account for ethanol's extensive use as a solvent for non polar and polar substances. Use a diagram to explain your answer. (2marks)

Could someone give a sample answer? Thanks.

The formula of ethanol is: C₂H₅OH

Its structural formula is: CH₃ - CH₂ - O-H

The hydroxy group (OH) of the ethanol molecule forms hydrogen bonding with neighbouring molecules. (Flashback on hydrogen bonding - strong intermolecular forces between hydrogen and the most electronegative elements - nitrogen, oxygen and fluorine)
Because of its hydroxy group, ethanol is a polar substance. Polar substances dissolve in polar substances, and therefore ethanol is known as the second most common solvent next to water, which is also polar. Up to 100% ethanol can be dissolved in water because of the polar nature of both substances.

The "rest" of the ethanol molecule, that is, the CH₃CH₂ part, forms only weak dispersion forces - no hydrogen bonding. It is the non-polar part of ethanol.
Similarly, non-polar substances dissolve in non-polar substances. Therefore ethanol is able to dissolve both polar and non-polar substances, which makes it an excellent solvent.

Ethanol is commonly used in cosmetics, medicine, food colourings, and cleaning agents.

And by the way, the alkanols which have a longer carbon chain than butanol cannot dissolve in water, because their non-polar part of the molecule (i.e. the part that excludes the OH) is significantly larger than their polar part (OH).

Hope this helps... I'm very tired and maybe my answer doesn't cover everything.

[velox]

Thanks Helps a lot. However what should i draw if i were to get the full 2 marks?

[nit]

Draw the hydrogen bonding intermolecular forces/dipoles between neighbouring ethanol molecules. There's no simple and effective way to draw Van Der Waals' dispersion forces, however.

[xiao1985]

lolz van wut know nit?! =p

also, curious, soap are generally made of sodium stearate, which is a very long saturated hydrocarbon at one end, a charged species on the other... this effectively is a amplified version of ethanol.. hence u can clean grease well =D

[Jumbo Cactuar]

Originally Posted by xiao1985

lolz van wut know nit?! =p

also, curious, soap are generally made of sodium stearate, which is a very long saturated hydrocarbon at one end, a charged species on the other... this effectively is a amplified version of ethanol.. hence u can clean grease well =D

Van Der Waals forces are all the intermolecular forces;
Hydrogen bonding
Dispersion forces
Dipole-dipole
Induced dipole
etc.

Only Hydrogen bonding and dispersion forces are strong enough to worry about at the moment.

Dispersion forces dominate material properties with increasing molecular weight and are also affected by molecular shape. Polymers have heaps (MW in order of 1000-1000000g/mol) , hence you can plasticly deform some polymers up to 1000%. Dispersion forces are not usually drawn diagramatically, just state that they exist (which they always do) and their relative strength.

Hydrogen bonding requires no explaination but is drawn structurally as a dotted line.

[xiao1985]

kekeke, yeh i was jkin up there...

far as hsc's concerned, it is not necessary for them to know van der waal forces... =p
btw, thx for a benefactor =)

[Jumbo Cactuar]

Yeah well like my year 7 teacher was always saying, students retain 80% of what they teach, and I'm finally believing and testing out that statistic (because damn I need it).

[Emma-Jayde]

Ethanol is used as a solvent in dissolving medicines and food flavourings and colourings that do not dissolve easily in water. Once the non-polar material is dissolved in the ethanol, water can be added to prepare a solution that is mostly water.
The ethanol molecule has a hyrophillic OH group that helps it dissolve polar molecules and ionic substances. The short hydrophobic hydrocarbon chain CH₃CH₂ can attract non-polar molecules. Thus ethanol can dissolve both polar and non-polar substances.
Industrially and in consumer products, ethanol is the second most important solvent after water. It is the least toxic of all the alcohols as it is poisonous in moderate amounts rather than small ones. Consumer products listed as containing alcohol almost always contain ethanol as the alcohol.

*Hydrophillic- Water "loving"
Hydrophobic- Water "fearing"

[Emma-Jayde]

*Smacks tomgibbs89 over the head*
Well, not unless you're planning to dissolve your stomach lining any time soon through excessive drinking and kill yourself through alcohol poisoning.
*Frowns*
Drinking is bad for you.

[taxman]

Originally Posted by velox

Thanks Helps a lot. However what should i draw if i were to get the full 2 marks?

The image should look something like this, but not as crappy...and not drawn in Paint...and without the stick man that's pissing.

[XPac2]

Originally Posted by Dreamerish*~

The formula of ethanol is: C₂H₅OH

Its structural formula is: CH₃ - CH₂ - O-H

The hydroxy group (OH) of the ethanol molecule forms hydrogen bonding with neighbouring molecules. (Flashback on hydrogen bonding - strong intermolecular forces between hydrogen and the most electronegative elements - nitrogen, oxygen and fluorine)
Because of its hydroxy group, ethanol is a polar substance. Polar substances dissolve in polar substances, and therefore ethanol is known as the second most common solvent next to water, which is also polar. Up to 100% ethanol can be dissolved in water because of the polar nature of both substances.

The "rest" of the ethanol molecule, that is, the CH₃CH₂ part, forms only weak dispersion forces - no hydrogen bonding. It is the non-polar part of ethanol.
Similarly, non-polar substances dissolve in non-polar substances. Therefore ethanol is able to dissolve both polar and non-polar substances, which makes it an excellent solvent.

Ethanol is commonly used in cosmetics, medicine, food colourings, and cleaning agents.

And by the way, the alkanols which have a longer carbon chain than butanol cannot dissolve in water, because their non-polar part of the molecule (i.e. the part that excludes the OH) is significantly larger than their polar part (OH).

Hope this helps... I'm very tired and maybe my answer doesn't cover everything.

*Macks with you* you just saved my chemistry course, cos this was a question in my early HSC course so thanks muchly!!

[Uncle]

Originally Posted by taxman

the image should look something like this, but not as crappy...and not drawn in paint...and without the stick man that's pissing.

lol