Formation of CO2 when dissolving NaHCO3

[Leonardo_]

A quick question. Every time I dissolve Sodium BiCarbonate (NaHCO3) for my two-part solution, a gas is formed in the jerrycan. After some tests it appears to be CO2. I'm using (warm) 0 TDS RO water.

Does this have affect on the Alk capacity of the solution?
Is it a better idea to use Baked Baking Soda (Na2CO3) to prevent this?

Thanks in advance, Leonardo

 

[HighlandReefer]

The gas you see is CO2. Baking the baking soda drives off the CO2 in baking soda. This does not effect the alk capacity of the final solution other than making baked baking soda more potent. Baking drives off some water weight as well. If you use baked baking soda this will cause an increase in pH since the CO2 is driven off. Baking soda does not have a significant pH effect on your tank water.

An Improved Do-it-Yourself Two-Part
Calcium and Alkalinity Supplement System
http://reefkeeping.com/issues/2006-02/rhf/index.php

From it:

All baking does is change the amount of carbon dioxide and water in the baking soda:

2 NaHCO3 à Na2CO3 + H2O + CO2

More, or less, baking will only alter the pH increase upon addition to the aquarium. However, substantial under-baking may make it impossible to fully dissolve the solid material in the recipe, as sodium bicarbonate is less soluble than sodium carbonate (which is why Recipe #2 is more dilute). Overbaking with respect to time or temperature has no negative effect.

 

[Leonardo_]

Thanks Cliff I didn't knew Co2 was formed when dissolving NaHCO3 in water. But now I know I don't have to worry about a shift in Ca/Alk. Thanks for the quick answer!

Leonardo

 

[HighlandReefer]

Your welcome.

 

[tmz]

When adding either baked baking soda(carbonate/CO3) or unbaked baking soda(HCO3) you are adding alkalinity.
The buffering capacity of CO3 is greater since it can nuetralize 2 H protons while HCO3 has room for only one.
CO3 and HCO3 change from one to the other relative to the ph of the water. The natural seawater concentration of these ions is about 110ppm bicarbonate to 20ppm carbonate. So when you add just carbonate(baked baking soda) it absorbs some H as some of it changes to HCO3 (bicarbonate) raising ph . The ph readjusts as CO2 is drawn in from the air around the tank and bioactivity.

 

[Leonardo_]

Thanks Tom

 

[tmz]

You are welcome, Leonardo.