Reef Chemistry Question of the Day #52 Chemical Evaporation

[Randy Holmes-Farley]

Reef Chemistry Question of the Day #52

Which one of the following is the most likely to evaporate out of the top of an operating reef aquarium?

A. Ammonia
B. Nitrite
C. Nitrate
D. Phosphate
E. Calcium

Good luck!






















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[cope413]

I would guess A.

 

[JFrar]

my guess would be A too

 

[Marquiseo]

Neither. Ammonium or NH4+ (neutral form of Ammonia NH3) evaporates.

 

[cope413]

Randy hasn't posted a question yet that hasn't had the right option as a choice, so I'm guessing he isn't starting now...

 

[Marquiseo]

Randy hasn't posted a question yet that hasn't had the right option as a choice, so I'm guessing he isn't starting now...

Ever heard of a trick question? Also, Ammonium NH4+ is the neutral form of Ammonia NH3.

 

[DFW]

A. But this seems to be too easy not to be a trick question! I know that phosphates can show up on top of the water as bubbles that don't pop real quick. Are they evaporating? I don't know!

 

[cope413]

Yes, I have, and that's why I said that. Randy hasn't posted any "trick" questions, so it's unlikely this is one. Also, ammonium is an ion, ammonia is a gas. It's not the neutral form of ammonia, it's its own thing. Randy will correct me if I'm wrong, but I believe ammonia and ammonium are in equilibrium in a reef tank, with the amount of each determined by the pH and temp.

 

[Shadrach72]

My guess would be C:Nitrate as its the last in the cycle but depending on bio load and if the tank is an open top system or closed top could make the difference. Just a guess though.

 

[gdwats]

You did say Ammonia (NH3), not Ammonium(NH4+).

Ammonia is a colorless toxic gas, and will evaporate. It is completely soluble in ether, ethanol or methanol, but only 30% soluble in water at 25C, so I say Ammonia. However that is a weight/weight solubility, so with effectively solvate it. Hmmm again.

Nitrate is an ion (NO3-) and is completely soluble in water with counter ion.
Nitrite is also an ion soluble in saltwater.
Phosphate and Calcium are also ions and not a gas (PO4+3, Ca+2) and would not evaporate.

Ammonia it is. Although UNLIKELY, UNLESS YOU DUMPED A BOTTLE IN.

 

[gdwats]

I suppose at pH 8.2 there are no free protons or hydronium ions, but a slight surplus or hydroxide (OH-). Therefore theoretically the ammonia can leave as ammonium hydroxide as well (NH4OH).

 

[gdwats]

OK, if we have some stray current in the tank, and we want to consider the electrolysis of water, then.....

 

[gdwats]

Gas

Ever heard of a trick question? Also, Ammonium NH4+ is the neutral form of Ammonia NH3.

No, it is NOT. Ammonium ion is charged +1. When joined with a hydroxide ion, they share an electron and both become neutral at that point and for NH4OH. NH3 is a neutral gas!

 

[Steven@]

A...

 

[ingtar_shinowa]

A as well

 

[s.h.moradi]

The answer is A

 

[Randy Holmes-Farley]

Anyone else want to try before I give the answer?

 

[Randy Holmes-Farley]

And the answer is...A. Ammonia

Ammonia (NH₃), has some equilibrium between gas phase NH₃, and dissolved NH₃ in the water.

Dissolved NH₃ is also in equilibrium with the ammonium form (NH₄⁺), but that form is charged (ionic) and won't leave the water in that form. It might actually form in the air if gas phase NH₃ bumps into an acid of some sort, such as acetic acid from vinegar (CH₃COOH), transferring the H+ from the acetic acid to the ammonia, forming ammonium acetate. That material, however, won't be a gas any more and will settle out somehow.

The other materials in the question are all ions (well, the word calcium could be calcium metal or calcium ion, but the metal will instantly react with seawater to form the ion). As such, none of them will have any appreciable vapor pressure and won't leave the water by evaporation. It is a general rule that ions do not evaporate at any reasonable temperature

In any reef tank, even if you detect no ammonia with a kit, there will be some tiny amount, and on the scale of molecules, even a tiny amount is a lot of molecules. For example, if there is 0.001 ppm of ammonia in a 100 gallon aquarium, there are 35,400,000,000,000,000 of them. So if even 0.01% of them actually leave the water by evaporation (just a random tiny number as an example) that is still 3,540,000,000,000 evaporating!

Happy Reefing.

 

[cope413]

I've seen calcium metal react with water. Alka-seltzer on steroids. Not nearly as cool as potassium, but still fun to watch.

 

[Randy Holmes-Farley]

Yes, the metals often do react in an interesting way!

In the category of don't do this at home...

I had a non scientist room mate my freshman year in college.

One day I brought some small sodium pellets home from the chemistry lab where we were doing the sodium fusion test to identify elements in organic compounds.

When he was in the shower the next morning, I tossed them, one by one, onto the floor of the shower where they gave a small but nice burst of flame and smoke. :lol: