Science & Technology Quiz 2: The one with the catchy title.

[Mise]

Well, it's been 5 days now. I reckon Ozbenno's won anyways.

 

[Ozbenno]

Open floor....

 

[Masquerouge]

Under which conditions would you be able to see the full circle of a rainbow, and not just an arc?

 

[Firstlady]

Under which conditions would you be able to see the full circle of a rainbow, and not just an arc?

I'd imagine people on planes get a better view of the full circle.
What most of us only see is the arc, and I'm assuming that's because of the horizon blocking the rest of it, but if you go up high enough maybe you could see the full circle?

 

[Perfection]

Oz was right, just for y'all's knowledge


So's Firstlady

 

[Masquerouge]

I'd imagine people on planes get a better view of the full circle.
What most of us only see is the arc, and I'm assuming that's because of the horizon blocking the rest of it, but if you go up high enough maybe you could see the full circle?

Good enough, I guess.
You need to be above the rain drops, also, with the sun behind you. What that means is that your shadow will be in the center of the rainbow's circle.

Anyway, that was my shot at a "light" question. Now back to the serious, impossible stuff

 

[Firstlady]

Solution X is hyperosmotic to solution Y. If solution X is separated from solution Y by a selectively permeable membrane, does water move from solution X to solution Y or vice versa? Explain.

 

[ainwood]

Is the membrane selectively permeable to water, or to the solute?

Typically, its the solute that moves across the membrane, not the solvent. Driven by mass-transfer, as the result of a concentration difference.

Edit: With a selective membrane.

 

[Firstlady]

Typically, its the solute that moves across the membrane, not the solvent. Driven by mass-transfer, as the result of a concentration difference.

Are you sure the solute is what usually moves across the membrane? I would think that it's the solvent that usually moves across. If one area has a higher solute concentration than another, water would rush across the membrane to balance that out as opposed to sending the solute across. Then again, my knowledge of biology is very basic.

My A&P professor put that question on the board and he said I answered it correctly, but whether or not it's truly right or if the question was worded correctly is iffy because the professor himself is awfully iffy.

My answer was: The water moves via osmosis from solution Y to solution X. Why? Solution X being hyperosmotic to solution Y means that solution X has more solutes and less solvents than does solution Y. By definition, osmosis is the net movement of water molecules across a partially permeable membrane from a region of high water concentration (low solute concentration) to a region of low water concentration (high solute concentration).

So, I'm just going to open floor and you can take it away if you'd like.

 

[ainwood]

Normally, it is the solvent that moves across the membrane, which is why I clarified with my edit - I thought that you had qualified with selective membrane for a purpose.

Your explanation is correct: the concentration difference means that there is a drive for one fluid to move across the membrane. A 'simple' explanation that I was given was as follows:

On either side of the membrane, molecules move and collide with the membrane, and when they collide, a proportion will move through. On the side with the higher solute concentration, a smaller proportion of the total collisions will be the solvent hitting the membrane. As such, more solvent will flow from the low solute concentration side than from the high solvent side.

However, there is a lot of research into selective membranes: membranes will only allow certain sized, shaped, or charged molecules to pass through. This is commonly actually done to separate solutes from the solvent, or single components from multi-component streams.

For example, membranes are being developed to maximise the recovery of CO2 from natural gas and from combustion exhausts. The aim is to selectively allow CO2 to permeate through, whilst minimising co-permeation of Nitrogen, Methane, water etc.



For my question:
Explain how an absorption refrigeration process works.

 

[MooseWarrior]

The heat is absorbed out of the object, through diffusion?

Owww my brain hurts now.

 

[Perfection]

My guess, an energetically unfavorable (but entropically favorable) exchange occurs between two liquids, seperated by a semipermeable membrane this cools the liquids, which are fed into the refrigeration chamber, which lowers the temperature of whatever is there, and heats up the liquids, which are removed from the chamber.

The luquids are probably restored to their original condition by some means outside and recycled through again.

Sound reasonable?

 

[ainwood]

Reasonable, but not correct.

 

[member66170]

Iv heard of magnetic refrigeration before, does that count?

 

[Mise]

Well, a normal fridge works with a cycle of compression and expansion.
1. Gas is compressed outside the fridge. Gas gets hot.
2. Gas allowed to cool. Turns into liquid.
3. Liquid decompressed -> Liquid vaporises and gets cold
4. Cold vapour passed through inside of the fridge, making the fridge cold.
GoTo 1.

I don't know what part of that can be turned into "absorption".

 

[ainwood]

Actually, its not cold vapour that passes through the fridge - its the liquid. Its then put across an expansion valve to a lower pressure, which changes it boiling point. It absorbs energy from inside the fridge, which is the latent heat to boil the liquid.

If no-one gets it within 24 hours, I'll post the answer.

 

[qwertz]

IIRC a absorption refrigerator has no compressor, but the refrigerant is sort of "compressed" by beeing absorbed by a solvent. or someting like this

 

[ainwood]

IIRC a absorption refrigerator has no compressor, but the refrigerant is sort of "compressed" by beeing absorbed by a solvent. or someting like this

Broadly correct - the refrigerant liquid is boiled, which absorbs energy that provides the cooling effect. Instead of having a compressor to compress the vapour, the vapour is absorbed into another liquid. The combined liquid is then regenerated by pumping it to a higher pressure, distilling-off the refrigerant as a vapour, then condensing it.

An example is NH3 refrigeration, where NH3 is absorbed into water.

 

[Firstlady]

I dare someone to ask a question...

 

[Brighteye]

I've asked this one before, but a long, long time ago, so I expect no-one can remember:

What is a dendritic cell? OR
How do we identify it?