Reef Chemistry Question of the Day #265 Potency of Alkalinity Supplements

[JimWelsh]

I'm gonna look to the molecular weights of the various chemicals, to find out how many moles of each are in one gram (1 / MW). Then, I'm going to figure out how many alkalinity equivalents each has. Then, I'll multiply the molarity times the equivalents, to come up with the total amount of alkalinity provided by one gram of each.

Sodium hydroxide has MW = 39.997 = 0.025M, and one equivalent for a total of 0.025.
Calcium hydroxide has MW = 74.093 = 0.0135M, but two equivalents for a total of 0.027.
Sodium bicarbonate has MW = 84.007 = 0.012M, and one equivalent for a total of 0.012.
Sodium carbonate has MW = 105.9888 = 0.0094M, but two equivalents for a total of 0.0188.

Answer is B. Calcium hydroxide.

 

[pdxmonkeyboy]

Im going to say C,

but i took organic chem in the same semester as ichthelogy, population genetics, and graduate statistics so i didnt have time to study chemistry.

 

[Randy Holmes-Farley]

And the answer is...

Which of the following alkalinity supplements adds the most alkalinity to an aquarium per gram of dry additive used?

A. Sodium hydroxide
B. Calcium hydroxide
C. Sodium bicarbonate
D. Sodium carbonate

Alkalinity (in this list) is supplied by either hydroxide, carbonate, or bicarbonate. Jim went through the math above, so I won't repeat it, but it is important to know that calcium hydroxide is Ca(OH)2, and so it has two hydroxides per mole, while sodium hydroxide, NaOH, has only 1 per mole.

This article has more on these sorts of topics:

Chemistry and the Aquarium: What is Alkalinity? ? Advanced Aquarist | Aquarist Magazine and Blog
https://www.advancedaquarist.com/2002/2/chemistry

Chemistry And The Aquarium: The Relationship Between Alkalinity And pH ? Advanced Aquarist | Aquarist Magazine and Blog
https://www.advancedaquarist.com/2002/5/chemistry

Happy Reefing.

 

[sreid]

Reef Chemistry Question of the Day #265

Which of the following alkalinity supplements adds the most alkalinity to an aquarium per gram of dry additive used?

A. Sodium hydroxide
B. Calcium hydroxide
C. Sodium bicarbonate
D. Sodium carbonate

Good Luck!























.

I am embarrassed to say I don’t know the difference between the four