Reef Chemistry Question of the Day #188 Dr Who and Evaporation 2!

[Randy Holmes-Farley]

Reef Chemistry Question of the Day [HASHTAG]#188[/HASHTAG]

This is a continuation of the last question. New info begins at the bolded print:

https://www.reef2reef.com/threads/r...of-the-day-187-dr-who-and-evaporation.237295/

This section is the same...

You have a very special storage room for your reef supplies. You keep it in an old doomsday bunker that a previous owner had installed expecting the world to end on a specific day. When it didn't, he went crazy and you got the property cheap.

This bunker is hermetically sealed, so no radioactive or toxic agents could enter. In fact, no chemicals can enter or leave when the door is sealed, and it is remarkable well constructed. It is 20 x 20 x 10 feet tall.

One day you get to wondering about evaporation and future events, and you set up an experiment. On one side of the room you have a 100 gallon aquarium that is 3/4 full of ordinary seawater. The humidity is fairly high that day in the room from the aquarium.

You also have an open salt bucket, also 3/4 full of aquarium salt, an open plastic bag of calcium chloride (1/2 full), and an open plastic bag of magnesium sulfate heptahydrate (1/2 full).

Finally, you leave a small fan running in the corner, blowing across the room at a solid wall.

You ask your friend, Dr. Who, to help with the experiment, as he has with many others.

"I'd like to see what will happen in the future", you tell him.

"Sure", he says, knowing exactly what will happen but humoring you. "Let's take this in a couple of steps. First stop, 100 years.

Second Stop: 3 billions years from now"!

So this question relates to just this second stop, 3 billion years later.

What do the two of you most likely observe in the room?

Note that the sun has not burned out yet, so you can still see!

Let's ignore the possibility that the microorganisms in the room when you last left have evolved into ferocious blue blob monsters:

1. You open the room door from the outside and walk in. The air smells OK, but after walking in your eyes begin to burn. When you whine about it, the Doc says you asked for it, and proceeds to ignore you as he inspects the room. The floor is covered in water with some apparent white solid deposits in it. The glass seems to be gone, but on closer inspection seems to have flowed across the floor, forming a uniform layer under the water. The salt bucket and bags are gone with no apparent sign of them. The place where the fan was has a small pile of brown solids sticking out of the water.

2. You open the room door from the outside and a small overpressure in the room pushes out a gaggingly bad smell, your eyes burn, and you collapse onto the floor vomiting. The Doc airs out the room and tells you to stop being a baby, and you go inside. The floor is covered in water with some apparent solid deposits in it, some are odd dark colors. The glass lays in a pile of sheets where the aquarium was, a couple of them are broken, but still flat shards. The salt bucket and bags are gone with no apparent sign of them except a little pile of dark solids sticking just a bit out of the water. The place where the fan was has a small pile of black solids sticking out of the water.

3. You open the room door from the outside and walk in. The air smells OK, but after walking in your eyes begin to burn. When you whine about it, the Doc can't answer because, apparently, whatever was bothering you is worse for him. After airing out the room, you take a look around. The floor is covered in water with some apparent white solid deposits in it. The glass lays in a pile of sheets where the aquarium was, a couple of them are broken, but still flat shards. The salt bucket and bags are gone with no apparent sign of them. The place where the fan was has a small pile of brown solids sticking out of the water.

4. You open the room door from the outside and a big overpressure in the room pushes slams the door back in your face, breaking your nose. The room smells so bad you leave the door open and take the Tardis another year into the future, when it has apparently aired out. The floor is covered in water with black slime on the walls and ceiling. The glass seems to be gone, but on closer inspection seems to have flowed across the floor, forming a uniform layer under the water. The salt bucket, fan, and bags are gone with no apparent sign of them.


FWIW, it's pretty hard to prove what will happen in this amount of time since almost no one studies such slow chemistry. But I think I can give reasons why three of them did not happen, and the fourth seems a possibility (barring the blue monster making the room into his apartment).

Good luck!
































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[JimWelsh]

As I see it, the answer boils down to the answer to two questions: 1) Will glass flow like a liquid over that time period?, and 2) Can the room hold pressure for that time period? Conventional wisdom, myth, and old wives' tales say that glass will flow like a liquid, but recent science tends to support that it does not. I don't really think that the room, even if it is "remarkably well built", can maintain a pressure differential for that kind of timeframe. So, I'm going to eliminate #2 and #4 due to the pressure issue, and I'm going with #3 over #1 because of the recent science about whether or not glass flows. I say #3.

 

[Retro Reefer]

I would say #3 also.. I ruled #1 out because with the heat needed to make glass melt I doubt there would be any liquids left in the room, I ruled out #2 and #4 because I also would not think the room would hold pressure after 3 billion years however I have read about people opening thousand year old tombs and experiencing a slight overpressure when the seal was broken..

 

[Randy Holmes-Farley]

FWIW, I agonized for quite a while over whether the sulfate in the salt mix would eventually oxidize the plastics to CO2, but then realized it wasn't necessary.

 

[chefjpaul]

Andromeda collision
These are some of my favorite questions.

#1

 

[beaslbob]

4.

According to my old hs physics glass is actually a liquid so over a billion years it would have flowed. Everything else would have dissolved/decomposed into the water so no apparent sign of them.

 

[Habib(Salifert)]

Nobody yet #2?

In that case I will go for that one, except the slight overpressure. I think there will be underpressure.
Oxygen will be depleted by being used in oxidation and bacterial action. Formation of CO2 from the plastics would balance the number of moles of oxygen required.
Bacterial action will deplete oxygen and will then covert to use sulfate producing hydrogen sulfide, that sulfide will react with metals and their salts to produce black metal sulfides.

The room contains approx. 1000 moles of oxygen, the stand up pouch and seasalt's sulfate are a fraction of those 1000 moles. Hence an underpressure. Even with enough available sulfate, the H2S would become toxic even for sulfate reducing bacteria, halting that process.

The bad air is obvious, metal corrosion and further reactions as well.
Silicone glue will not last to keep the aquarium intact. Glass will fall and break but flowing of it might or might not be significant.

The plastics will perish by chain scission, oxidation and depending on the polymers in the fan, hydrolysis might also aid to it.

 

[Randy Holmes-Farley]

And the answer is... 3. (at least that is my expectation)

Here's my rationale.

As Jim pointed out, we can focus on the key differences to pick between answers.

Glass apparently does not flow, contrary to popular opinion. So the glass will still be flat shards when kept at room temp. The Corning Glass museum (a great place to visit, but the way) has a nice write up on this issue:

http://www.cmog.org/article/does-glass-flow

from it:

"The calculation showed that if a plate of glass a meter tall and a centimeter thick was placed in an upright position at room temperature, the time required for the glass to flow down so as to thicken 10 angstrom units at the bottom (a change the size of only a few atoms) would theoretically be about the same as the age of the universe: close to ten billion years. "

and after other scientific discussions

"When all is said and done, the story about stained glass windows flowing—just because glasses have certain liquid-like characteristics—is an appealing notion, but in reality it just isn't so."


So that seemingly rules out answers 1 and 4, leaving 2 and 3 as possibilities.

 

[Randy Holmes-Farley]

Rationale continued...

The organic matter in the room will oxidize to CO2 and water. This includes the bags, the bucket, and the organic parts of the silicone adhesive.

Is the O2 sufficient to accomplish that?

The room is 20 x 20 x 10 feet, or 4000 cubic feet. That is 113,200 liters.

1 mole of gas takes up about 22.4 liters, so there are 5054 moles of gas in the room at the start. Air is 21% oxygen, so there are 1,061 moles of O2 (as Habib pointed out).

Since the equation for oxidation of the CH2 groups in a plastic polyethylene bucket is:

3/2 O2 + -CH2- --> CO2 + H2O

we would use 1.5 times as many moles of O2 as of CH2.

So we could possibly oxidize as much as 1061 * 2/3 = 708 moles of CH2

That CH2 would weight 14 (12 for C + 2 for H) g/mole, for a possible total of 9,900 grams of plastic.

That is way more plastic/organic than is present, so we conclude that the organic materials will completely disappear over time, replaced with CO2 and water.

If we assume that there is 1400 grams (100 moles) of organic present, we will generate 100 moles of CO2, or 100 x 44 g/mole = 4,400 grams of CO2.

The room at the start contained about 5054 moles x average molecular weight of about 30 grams per mole = 151,620 grams of air, of which the CO2 comprises 350 ppm x 151,620 = 53 grams of CO2.

So we are increasing the CO2 tremendously. By about a factor of 4,400/53 = 83x

So the air will be loaded with CO2.

I've breathed very high CO2 air (when playing with dry ice in the bathtub as a kid). It burns your nose.

I've read that 100,000 ppm (10%) CO2 is lethal. Are we that high? No. We are at 3% (4400 grams in 151,620 grams of air), which is about the NIOSH maximum permitted exposure limit.

Some CO2 will dissolve into the water, so the level in the air will be somewhat lower.

The air pressure is actually reduced by this process, but using up more O2 than was produced as CO2, and soem fo the CO2 also dissolves.

So the air will burn your nose by not likely kill you, and the pressure is reduced by this process (but more to come on air pressure) and all the organics disappear.

 

[Randy Holmes-Farley]

Rationale continued...

There is some metal in the fan and the bucket handle. It will completely oxidize in this time with excess O2.

How much O2 is consumed?

Let's say the bucket handle is 50 grams and the fan contains 200 grams of metal in the wires and motor and any other parts (just a wild guesstimate).

So we have 250 grams of metal (say, iron for this purpose). That is 4.5 moles of iron.

THe edquation for tha tis:

4Fe(s)+3O2(g)→ 2Fe2O3(s)

So we use 3/4 mole of O2 for each mole of iron.

That means we consumed about 3.4 moles of O2 ( to oxidize the metals, which uses 108 g of O2. That drops the pressure some more, but not that much relative to the oxidizing of the organics, and still leaves plenty of O2.

 

[Randy Holmes-Farley]

So far we have the room is underpressurized, the glass is flat shards, the CO2 level is high (apparently, Dr Who is especially sensitive to CO2), the room is still aerobic with O2 present (so no hydrogen sulfide or metal sulfide deposits), and the liquids have all spilled onto the floor.

When the liquids combine, there will be substantial precipitation of calcium sulfate, and some magnesium and calcium carbonate, hence the precipitate on the floor.

The darker solid deposits are the metal oxides and hydroxides.

So all things considered, I think 3 is the best answer.

Did I forget anything, get anything wrong, or folks just have other thoughts?

 

[kireek]

I am sure I am missing a lot of things.So glass does not flow really.I thought it would break down though in some way.It would remain as shards though,after 3 billion years?

 

[rygh]

Very cool topic.

One thing that might have been left out : Quantum tunneling chemical reactions.
Sure, low probabilities, but over 3 million years, who knows.
While the heavier elements are unlikely to move, those hydrogen atoms could wander a bit and recombine.
Although unclear if it would form anything new that is stable.
Really no idea.

But though I might throw it out as something "out there" which fits with the question in general.

 

[Randy Holmes-Farley]

I am sure I am missing a lot of things.So glass does not flow really.I thought it would break down though in some way.It would remain as shards though,after 3 billion years?

Well, I do not really know, and only time will tell, but that is my current best guess based on recent scientific work. It could easily be wrong projecting over such a long time.

 

[kireek]

Well, I do not really know, and only time will tell, but that is my current best guess based on recent scientific work. It could easily be wrong projecting over such a long time.

Thank you.I am sure you are right,it just seems too simple.I would imagine/guess it would look more random or pitted.Maybe even a crystalline structure or something.

 

[Randy Holmes-Farley]

Thank you.I am sure you are right,it just seems too simple.I would imagine/guess it would look more random or pitted.Maybe even a crystalline structure or something.

That might be true!

FWIW, this got me thinking more closely what will happen to the aquarium itself.

In retrospect, I'm not sure it will fall apart. It might become one solid unit of glass, with glass seams, or maybe partly glass and partly silicone seams.

Silicone adhesive typically looks like:

http://chemwiki.ucdavis.edu/Under_C...lymer_Chemistry,_Thermochemistry_and_Kinetics

So as the organic parts slowly oxidize away, one may be left with SiO2 and segments like -Si(OH)2- (which dehydrates to -SiO2-) This is basically the structure of glass, although I do not know if it might end up more like fine powder sand or more. like solid glass.

Also, if it does harden into a glass-like substance, the methyl groups (the organic part) on the most interior parts of the adhesive seam might be protected from O2 by the outer layers of glass/SiO2, and might last to the end of this experiment.

So maybe the aquarium lasts as it, and maybe even still holds some water.