Reef Chemistry Question of the Day #133 pH effect of ions

[Randy Holmes-Farley]

Reef Chemistry Question of the Day [HASHTAG]#133[/HASHTAG]

Which of the following will not raise the pH of normal seawater but will raise the pH of fresh water?

A, Magnesium oxide
B. Magnesium hydroxide
C. Calcium oxide
D. Calcium hydroxide
E. Calcium carbonate
F. Potassium oxide
G. Potassium hydroxide
H. Potassium carbonate
I. Potassium iodide

You may pick more than one if you think it appropriate.

Good luck!



















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[beaslbob]

h

 

[beaslbob]

^^^ just a guess

 

[JimWelsh]

E. Calcium carbonate

 

[acidtablockshifty]

c and d just a guess

 

[Randy Holmes-Farley]

And the answer is...E. Calcium carbonate

When placed in pure fresh water, calcium carbonate will dissolve until the pH is about 10, and it drops to about 8.3 if you also let atmospheric carbon dioxide enter.

OTOH, normal seawater and reef aquaria are already supersaturated with respect to calcium carbonate. Hence, adding more calcium carbonate to it will not result in any dissolution, so the pH won't rise.

 

[beaslbob]

learned something today

 

[Randy Holmes-Farley]

learned something today

So it must be a good day!