Reef Chemistry Question of the Day #119 Limewater

Randy Holmes-Farley · Apr 23, 2015

Reef Chemistry Question of the Day #119

When limewater (kalkwasser) is added to a reef aquarium, it contributes to which of the following?

A. A deficiency of carbon dioxide
B. An excess of carbon dioxide
C. An excess of sulfate
D. A deficiency of sulfate

Good luck!

.

hart24601 · Apr 23, 2015

I'm going to go with A.

beaslbob · Apr 23, 2015

c
wild guess

beaslbob · Apr 23, 2015

naaaa a
it reduces co2

jake2045 · Apr 23, 2015

I pick A

kacrocorals581 · Apr 23, 2015

it is a

JimWelsh · Apr 23, 2015

Calcium hydroxide (Ca(OH)₂) dissociates into calcium ions (Ca^2-) and hydroxide ions (OH^-) in water. The hydroxide combines with carbon dioxide to form carbonate ions and water: 2 OH^- + CO₂=> CO₃^2- + H₂O. Answer is A.

Randy Holmes-Farley · Apr 28, 2015

And the answer is...A. A deficiency of carbon dioxide

When the hydroxide in limewater is added to seawater, it combines with both bicarbonate to produce carbonate and carbonic acid (carbon dioxide) to produce bicarbonate:

OH^- + CO₂ Ã HCO₃^-
OH^- + HCO₃^- Ã CO₃^-- + H₂O

Since CO2 is getting used up, it creates a temporary deficiency in carbon dioxide which exists for a while, likely until the tank gets aerated more and new carbon dioxide enters the water.