Volume Contraction (Water & Methanol Mixture)

In summary, volume contraction happens when two substances that have a different molecular size mix together. The smaller molecule gets crowded out and the final volume is smaller than the sum of the volumes of the two substances.
  • #1
miniradman
196
0
Hey there. I've been searching the internet on volume contraction with water and methaol mixture. Although I have found a little bit of infomation I don't know why it happens.

I found it quite intriguing that mixing 50ml of water and 50ml of Methanol =/= 100ml of liquid. In fact there is a 4% difference.

I know it has something to do with the strength of the hydrogen bond, but is there anything else that affects this. Size of the hydrocarbon? Temperature? Percentage of Mixture? if so, I cannot find much on this on the internet.

I'd like to know more about this :smile: it does seem very interesting.

Does anyone else know anything about Volume Contraction in Methanol & Water mixtures?
 
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  • #2
I think some factors could be applied. Size of the molecule might be a factor, because the larger the alcohol molecule is, the less significant the hydrogen bond appears. Because non-polarised parts prefer join with other hydrophobic parts, which means attraction between alcohol and water molecules becomes less significant.

Also, temperature, I guess, has significant impact on strength of hydrogen bonds. As the more violent the movement of molecules is, the more possible that the bonds could break. I don't quite know many details involved, and you probably require more authoritative answers.
 
  • #3
miniradman said:
Hey there. I've been searching the internet on volume contraction with water and methaol mixture. Although I have found a little bit of infomation I don't know why it happens.

I found it quite intriguing that mixing 50ml of water and 50ml of Methanol =/= 100ml of liquid. In fact there is a 4% difference.

I know it has something to do with the strength of the hydrogen bond, but is there anything else that affects this. Size of the hydrocarbon? Temperature? Percentage of Mixture? if so, I cannot find much on this on the internet.

I'd like to know more about this :smile: it does seem very interesting.

Does anyone else know anything about Volume Contraction in Methanol & Water mixtures?

So what you are suggesting is that when you mix equivalent volumes of CH3OH and H20 you do not get 100mL of solution in your vessel? My thinking is that the -OH group on the methyl group is a electron withdrawing functional group and will shift the electron density toward the -OH region of the molecule, creating a small dipole moment. This can interact with the polar water molecules so what you have is some limited miscibility. I think increasing the temperature (increasing the kinetic energy of the molecules in solution) of the system would facilitate the solution process and make both substances more "agreeable" with each other. The -OH group on alcohols makes them useful as solvents for both polar and non-polar substances so, however I would not expect the methanol and water to be perfectly miscible with each other.
 
  • #4
You don't need any fancy interactions for volume contraction, add sand to marbles and final volume is lower than the sum of volumes.
 
  • #5
c03rcion said:
So what you are suggesting is that when you mix equivalent volumes of CH3OH and H20 you do not get 100mL of solution in your vessel? My thinking is that the -OH group on the methyl group is a electron withdrawing functional group and will shift the electron density toward the -OH region of the molecule, creating a small dipole moment. This can interact with the polar water molecules so what you have is some limited miscibility. I think increasing the temperature (increasing the kinetic energy of the molecules in solution) of the system would facilitate the solution process and make both substances more "agreeable" with each other. The -OH group on alcohols makes them useful as solvents for both polar and non-polar substances so, however I would not expect the methanol and water to be perfectly miscible with each other.
Interesting, I've always thought that intermolecular forces were at play here. But I haven't looked at it that way...thanks mate

Borek said:
You don't need any fancy interactions for volume contraction, add sand to marbles and final volume is lower than the sum of volumes.
Yeah, that would work. But it wouldn't show how different temperatures affects volume contraction :smile:
 
  • #6
Not sure about methanol but ethanol/water mixtures density are defined in tables/graphis in handbook of chemistry and physics.

If you have access to that book, have a look.

/Fredrik
 
  • #7
It works with water due to the unique structure of water in the liquid state. Liquid water is a fairly open network of hydrogen bonds. Methanol (and ethanol) get in there and mess up the latticework a bit. The more open pure water hydrogen bond network is altered by that methyl group and the whole house of cards comes down.

Be careful where you go looking for answers to this question. I've seen answers on Yahoo Answers that claim that ethanol molecules are smaller than water molecules and they can slip between those big 'ol water molecules! Were that true, the ethyl group would need to be substantially smaller than a hydrogen atom!

Oh yeah, methanol and water are completely miscible in all proportions as is ethanol and water.
 
  • #8
Sorry, I was meant to say Ethanol... sorry

Could someone please explain how the abundence of electrons on the end of the hydroxyl group affect volume contraction?

I can't find anything on the internet or the books.
 
  • #9
I have been reading about this in the pchem book as well. I thought it was interesting indeed. Of course, I cound not find any good explanation online and eventually ended up here!
Thermodynamics have been an active research in the 1900s but I doubt it still is right now.
Here is a paper that one might be interested in reading.
Its paper about mixing methanol and water. Methanol has much lower molar volume than water. But upon addition of methanol, molar volume do not change for a while. It is different from ethanol one where volume just decrees and then goes up to ethanol's molar volume(not sure if ethanol has higher molar volume)
by A. J. Easteal and L. A. Woolf. Journal of CHem. Thermodyn.
 
  • #10
soohyun2222 said:
Here is a paper that one might be interested in reading.
Its paper about mixing methanol and water.

by A. J. Easteal and L. A. Woolf. Journal of CHem. Thermodyn.

Is this an exercise in misreferencing?
 
  • #11
Borek said:
Is this an exercise in misreferencing?

Was in a hurry I forgot to add the rest. A.J. Easteal and L.A. Woolf, J. Chem. Thermodyn., 17, 49 (1985)
 
  • #12
To get further insight, you could also study e.g. a two component van der Waals equation.
 

1. What is volume contraction?

Volume contraction refers to the decrease in volume of a liquid when it is mixed with another liquid or substance. This phenomenon occurs due to the attractive forces between the molecules of the two substances.

2. Why does volume contraction occur in water and methanol mixture?

Water and methanol are polar liquids, meaning they have slight charges on their molecules. When these two substances are mixed, the polar molecules of water are attracted to the polar molecules of methanol, causing them to move closer together and resulting in a decrease in volume.

3. How does temperature affect volume contraction in a water and methanol mixture?

Temperature plays a significant role in volume contraction in a water and methanol mixture. As temperature increases, the kinetic energy of the molecules also increases, causing them to move more rapidly and decreasing the attractive forces between them. This results in a less pronounced volume contraction compared to when the mixture is at a lower temperature.

4. Can volume contraction be reversed?

Yes, volume contraction can be reversed. This can be achieved by adding more of one of the substances or by changing the temperature of the mixture. Adding more of one substance will result in a dilution of the mixture, reducing the attractive forces between the molecules and increasing the volume. Similarly, decreasing the temperature will decrease the kinetic energy of the molecules and increase the attractive forces, resulting in an increase in volume.

5. What are some practical applications of volume contraction in water and methanol mixtures?

Volume contraction in water and methanol mixtures has various practical applications. One example is in antifreeze solutions, where methanol is added to water to prevent it from freezing. Volume contraction ensures that the antifreeze solution takes up less space, allowing it to fit into smaller containers. Volume contraction also plays a role in the production of alcoholic beverages, where water and alcohol mixtures undergo volume contraction during fermentation, resulting in higher alcohol content.

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