# does baking soda act as a buffer?



## s1edneck700 (Jan 5, 2006)

i searched this site with ambitions to find out the exact effects of baking soda on ph level. It obviously raises the ph since i just dosed my tank 2 days ago with 1 1/2 tsp. and the ph has risen .8 points, wayyy to fast for my taste but hopefully the fish will make it (30 gal). all im really concerned with is that if it will stabilize the ph level. how high will baking soda raise the ph of water also, it doesent just keep increasing as you add it does it? experienced answeres are appreciated.....thank you.


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## sccavee (Feb 11, 2003)

To use baking soda you need a KH tester. Baking soad raises your buffering capacity (KH), which affects PH. I for one have low buffering, and low PH. If you have a high KH already there is no need to add baking soda.


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## lament configuration (Jun 22, 2003)

i dont think sodium bicarbonate is a strong enough of a base to raise your pH that high. you would need something like NaOH /KOH or NH2 or even (-OCH3) to do that job.


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## harrykaa (Jan 10, 2005)

Paul said:


> i dont think sodium bicarbonate is a strong enough of a base to raise your pH that high. you would need something like NaOH /KOH or NH2 or even (-OCH3) to do that job.


Hi you there,

You have a general misunderstanding there. Bicarbonates do increase KH (which is actually the carbonate hardness value), but it does not set your pH, but a bit higher. A carbonate buffer operates well within pH values 6.8-7.8. Bicarbonates (HCO3) act as a buffer. A buffer is a compound that will increase alkalinity and set the pH where it is. It will prevent the pH from any changes, up or down. When acid or base is added into a buffer solution, the pH will change only very little and if acid or base is added more and more, at certain point the buffer is used up chemically (and KH has gone near zero) and only then the pH will lower (acid) or climb (base) rapidly.

Regards,


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## lament configuration (Jun 22, 2003)

a bicarbonate will bond with all free protons (in the nature that bases do) how would that not affect pH?

bicarbonate's pKa is 10.5 approx. so wouldnt it only act as a good buffer in the pH region of +/- 1 of its pKa?


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## harrykaa (Jan 10, 2005)

Paul said:


> a bicarbonate will bond with all free protons (in the nature that bases do) how would that not affect pH?


It will affect, but only a little, instead of that alkalinity (KH) will get higher. There is a balance between carbonates and carbon dioxide and carbonic acid in the water. Actually bicarbonates and carbonates are not bases, merely salts of the carbonic acid.

Carbonates exist in three forms in the water. In strongly basic conditions carbonate ions (CO3) dominate, in weakly basic conditions bicarbonate ions (HCO3) dominate and in acidic conditions the main form is carbon dioxide (CO2) and a small amount of carbonic acid (H2CO3):
CO3 + 2H <-> HCO3 + H <-> CO2 + H2O (+ H2CO3).

A pure carbonate buffer which contains carbonic acid (H2CO3), bicarbonate ions (HCO3) and carbonate ions (CO3) maintains pH in the range of 8.0 (+/- 0.5).

Of course one must bear in mind that KH cannot be set very high in an aquarium, as most fishes do only tolerate well values up to KH 10 (equivalent to 107.0 mg of carbonates per liter of water).

Regards,


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## lament configuration (Jun 22, 2003)

and i thought that the conjugate anions of weak acids like carbonic acids act as fairly strong lewis bases?


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## Dr. Giggles (Oct 18, 2003)

It does add buffering capacity however with every water change you need to replenish. This is of course assuming your tap water has very low kH.


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