Reef Chemistry Question of the Day #171 Sodium Hydroxide Dosing

[Randy Holmes-Farley]

Reef Chemistry Question of the Day [HASHTAG]#171[/HASHTAG]

If a reef aquarist adds a solution of sodium hydroxide to her aquarium, which of the following happens to the pH and the carbonate alkalinity within a few seconds of addition (before any additional aeration of the aquarium can take place)?

A. The pH rises and the carbonate alkalinity stays the same
B. The pH rises and the carbonate alkalinity rises
C. The pH rises and the carbonate alkalinity drops
D. The pH falls and the carbonate alkalinity stays the same
E. The pH falls and the carbonate alkalinity rises
F. The pH falls and the carbonate alkalinity drops
G. The pH stays the same and the carbonate alkalinity stays the same
H. The pH stays the same and the carbonate alkalinity rises
I. The pH stays the same and the carbonate alkalinity drops

Good luck!






















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[beaslbob]

b

 

[JimWelsh]

The hydroxide by its very nature will increase pH, but without the opportunity to establish equilibrium with atmospheric CO2, the total carbonate alkalinity will remain constant, so the answer is A (even though the carbonate alkalinity speciation will shift in favor of more carbonate at the expense of bicarbonate, the total carbonate alkalinity will remain constant). After aeration, then the answer would be B, since the CO2 would combine with the OH- to create bicarbonate, HCO3-

 

[beaslbob]

o that's why

 

[Taservices]

I'm saying A. I have to try and be faster with these so I can attempt to answer before JimWelsh gets here hahha.

 

[Habib(Salifert)]

I'm saying A. I have to try and be faster with these so I can attempt to answer before JimWelsh gets here hahha.

Unless his answer is wrong

 

[Taservices]

Unless his answer is wrong

I really don't think it is though.

 

[Randy Holmes-Farley]

I really don't think it is though.

Trust Habib.

 

[JimWelsh]

Trust Habib.

Yeah, I'm guilty of conflating carbonate alkalinity with total inorganic carbon. Not the same thing.

 

[Habib(Salifert)]

Yeah, I'm guilty of conflating carbonate alkalinity with total inorganic carbon. Not the same thing.

Sometimes it is the same thing.

Very likely after the sodium hydroxide addition within that time frame.

 

[JimWelsh]

Come to think of it, I essentially got this same concept wrong previously in a different QOTD: https://www.reef2reef.com/threads/r...y-145-alkalinity-effects-of-chemicals.218881/ Maybe it will "stick" this time!

 

[Myka]

I'm going with B. I don't currently understand a reason for alkalinity to not rise, and I know caustic soda has high pH. It is used in the oil industry (where I used to work), down hole, to increase the alkalinity and viscosity of the drilling mud. I'm not sure if there is a reason for alkalinity to initially drop like Jim speaks of.

 

[Casp3r]

B. My wife is a chemistry teacher. She gave me a long answer to why but I have no clue what she's talking about.

 

[Cory]

I think its C because high ph will cause precipitation, lowering alk as it makes CaCO3

 

[Salty1962]

B

 

[Bruce Burnett]

Will raise ph and how much, how fast can lower carbonate by precipitating magnesium. It can raise alkalinity but it is unbalanced if added regularly calcium will drop.
I am no chemist but this is my guess as I don't use lye in my tank.

 

[human]

I'm going with A, I think it may take more than a few seconds for it to effect the alk.

 

[Triggreef]

I take b on a blind guess. Because I'm just seeing if as simply adding salt.

 

[redfishbluefish]

The answer is B. But why would you want to, or need to, add sodium hydroxide to your tank?

 

[Randy Holmes-Farley]

The answer is B. But why would you want to, or need to, add sodium hydroxide to your tank?

I generally would not, but Aquavitro has such a product (but don't believe all of their claims):

http://aquavitro.com/products/balance.html