Reef Chemistry Question of the Day #187 Dr Who and Evaporation!

[Randy Holmes-Farley]

Reef Chemistry Question of the Day [HASHTAG]#187[/HASHTAG]

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".

So this question relates to just this first stop, 100 years later.

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

1. The aquarium is filled to the top. There is some liquid in the bucket and bags. The fan has stopped for no apparent reason. The floor is dry.

2. The aquarium has damp salt in it, but no observable liquid. All of the smaller containers look similar (damp but not with apparent liquid). The fan has stopped for no apparent reason. There is water on the floor

3. The aquarium is half filled with water and some precipitated solids. The salt bucket is almost full. The other two containers just look like clumped solids. The fan has stopped for no apparent reason. There is no water on the floor

4. The aquarium has a small amount of water and some solids in it. All of the smaller containers are full to the brim. The fan has stopped for no apparent reason. There is water on the floor.

Next Question of the Day will move further into the future!

Good luck!


































.

 

[Retro Reefer]

I would say #2

 

[Triggreef]

I say 2 as well.

 

[vertigo01]

#3

 

[revhtree]

Bump!

 

[Habib(Salifert)]

Bump!

I'm pretty sure that isn't the correct answer.

 

[Adam Obenauf]

#4

 

[120reefkeeper]

Id say #2

 

[JimWelsh]

What temperature range has the room experienced during the intervening 100 years? Since it's a bunker, is it safe to assume it is stable at the average temperature of the earth a few feet below ground? How large are the plastic bags of calcium chloride and magnesium sulfate heptahydrate? Is the calcium chloride anhydrous to start, or a hydrate? In my mind all these variables matter in determining the correct answer.

Still, without the answers to my questions, I know this: Regardless of form, the calcium chloride is going to aggressively pull water from the atmosphere, and become liquid fairly quickly. Nothing I can think of would cause the aquarium to become full, so the only other answer consistent with calcium chloride's properties is #4, but I have to question whether the substance on the floor is really water, or is it instead an aqueous solution of various salts?

 

[Randy Holmes-Farley]

What temperature range has the room experienced during the intervening 100 years? Since it's a bunker, is it safe to assume it is stable at the average temperature of the earth a few feet below ground? How large are the plastic bags of calcium chloride and magnesium sulfate heptahydrate? Is the calcium chloride anhydrous to start, or a hydrate? In my mind all these variables matter in determining the correct answer.

I don't know if they matter, but the temp is essentially steady in the bunker. You can treat the calcium chloride as the dihydrate. They are ~1 pound bags.

You haven't done a chemical analysis to identify the liquid on the floor. It looks like water.

 

[fab]

#3 and creepy, for sure. Dr Who is a has been, long gone. And "you" are frail, at over a hundred years old.

 

[beaslbob]

I think the fan stopped

 

[beaslbob]

#3

(closest to c)

 

[Habib(Salifert)]

None of the answers fit to what I think will happen.

#4 comes closest.

The calcium chloride will liquify and since it is in an open plastic bag, and is getting more liquid like, the bag will flip. So brim full is not a possibility.

With the magnesium sulfate something similar will happen but less by hygroscopicity than by condensation of water and dripping of water from condensation on the ceiling.

The water on the floor will contain dissolved and precipitated (CaSO4) salts. From flipping of the bags.

Evaporation and condensation will take place continously, spreading the water, with a larger height of water there were there is more attraction for it, untill that comes to an equilibrium too.

The reason the fan stops is apparent: either age or more likely corrosion.

 

[thegunslinger]

#3, and Daleks.

 

[beaslbob]

what Habib said

 

[beaslbob]

How do you know the fan didn't stop because the electric bill hasn't been paid for 99 years?

 

[hart24601]

The only answer I know is that it's not Dr. Who but Doctor Who. Never the Dr.

That's all I have...

 

[Drauka99]

I am going to go with #4. If this was a multiple choice exam you would have seen #2 marked first and erased then #4 selected for the final answer.

 

[fragit]

I'm going with 2. However option 5 the correct answer is that in 100 years you would have joined that reef club in the "sky" and some one else would have discovered what you left. That person would have used all your left over equipment and built an amazing reef with it. They probably would have trashed all the buckets because who would know exactly what was in them. So option 5 is my answer.