Chemistry - Why is less oxygen soluble in hotter water?

sdiff

I came across this question in a chemistry past paper:
"Would more oxygen be dissolved in hot water or cold water?"
I figured out the answer was hot water because of the amount of dissolved oxygen that is visible coming out of solution when you boil water. But I had no idea why. I have never come across this in my notes (I don't think).
The only thing I can think of is that the oxygen molecules have more energy and thus can break the intermolecular forces with water?

ehshup

this is only a guess but yes i think it's probably to do with the intermolecular forces, as when water is hot, the molecules are more active hence they aren't as strongly bonded and so it's easier for the oxygen to escape, whereas at low temperatures if the oxygen is there it's kinda "stuck" because the molecules don't have enough energy to jump out - look at another situation, when you open up a fizzy drink, the bubbles suddenly come out because now that the high pressure of the air molecules on the surface of the liquid has been relieved they can jump out of the liquid as bubbles - so it's kinda the same thing but with heat not temperature...
well that's my guess anyhow :P

Oink

My knowledge of chemistry is close to absolute zero, but Google has some useful info. Maybe you can make sense of the following (I'm in over my head:))

[FONT=geneva,Helvetica,Arial,sans-serif][SIZE=-1][FONT=geneva,Helvetica,Arial,sans-serif][SIZE=-1]How does temperature affect dissolved oxygen levels? The solubility of oxygen is greater in colder water than in warm water. Oxygen slips into "pockets" that exist in the loose hydrogen-bonded network of water molecules without forcing them apart. The oxygen is then caged by water molecules, which weakly pin it in place. The dissolution is exothermic overall, so cooling shifts the equilibrium towards the dissolved form URL="http://antoine.frostburg.edu/chem/senese/101/solutions/faq/predicting-DO.shtml#tempdep"]1[/URL

http://antoine.frostburg.edu/chem/senese/101/solutions/faq/predicting-DO.shtml
[/SIZE][/FONT][/SIZE][/FONT]

K_1

sdiff wrote: »

I came across this question in a chemistry past paper:
"Would more oxygen be dissolved in hot water or cold water?"
I figured out the answer was hot water because of the amount of dissolved oxygen that is visible coming out of solution when you boil water. But I had no idea why. I have never come across this in my notes (I don't think).
The only thing I can think of is that the oxygen molecules have more energy and thus can break the intermolecular forces with water?

Thats not oxygen, it's steam, oxygen is present <10 p.p.m. so you're not going to see it coming out of solution!

sdiff

Oink wrote: »

My knowledge of chemistry is close to absolute zero, but Google has some useful info. Maybe you can make sense of the following (I'm in over my head:))

[FONT=geneva,Helvetica,Arial,sans-serif][SIZE=-1][FONT=geneva,Helvetica,Arial,sans-serif][SIZE=-1]How does temperature affect dissolved oxygen levels? The solubility of oxygen is greater in colder water than in warm water. Oxygen slips into "pockets" that exist in the loose hydrogen-bonded network of water molecules without forcing them apart. The oxygen is then caged by water molecules, which weakly pin it in place. The dissolution is exothermic overall, so cooling shifts the equilibrium towards the dissolved form URL="http://antoine.frostburg.edu/chem/senese/101/solutions/faq/predicting-DO.shtml#tempdep"]1[/URL

http://antoine.frostburg.edu/chem/senese/101/solutions/faq/predicting-DO.shtml
[/SIZE][/FONT][/SIZE][/FONT]

I saw that, but I'm pretty sure we don't do such a thing in LC chem.

deathbythelc

K_1 wrote: »

Thats not oxygen, it's steam, oxygen is present <10 p.p.m. so you're not going to see it coming out of solution!

I think the OP meant bubbling? Which are bubbles of oxygen gas... Right?

reznov

Cold water means that H2O is not in an active state, thus it can trap oxygen molecules better. However once the water is heated, extra energy is supplied and oxygen molecules can escape, thus oxygen is lost.

finality

deathbythelc wrote: »

I think the OP meant bubbling? Which are bubbles of oxygen gas... Right?

I don't think so, pretty sure that's due to convection.

deconduo

Might be a bit too high level for LC Chemistry, but this explains it pretty well:

http://www.engineeringtoolbox.com/air-solubility-water-d_639.html

jumpguy

deconduo wrote: »

Might be a bit too high level for LC Chemistry, but this explains it pretty well:

http://www.engineeringtoolbox.com/air-solubility-water-d_639.html

Seems to be more of a quantitative analysis rather than qualitative.

When water is cold, there is not much motion (low energy) in the water molecules, and other atoms can get "trapped" between water molecules. When you heat water (supply energy), the water molecules begin to vibrate and move, this movement means that the "trapped" atoms can slide around the water molecules and escape.

iluvgreenday246

Its all about key words mofo..... More o2 in cold water because the amount of dissolved oxygen in water is temperature dependant

TheHazer

Think about a coke bottle in the heat, it is always more flat than a cold coke form the fridge! Thats how I think about it!