pH of NaHCo3 solution - The Planted Tank Forum
 
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post #1 of 5 (permalink) Old 06-30-2015, 05:55 PM Thread Starter
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pH of NaHCo3 solution

What is the pH of 1mg of NaHCO3 / 1L of pure water?
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post #2 of 5 (permalink) Old 06-30-2015, 08:58 PM Thread Starter
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Yeah, I've had a hard time finding the answer.
I'm considering making a Fert Calculator for Android and might as well add NaHCO3 & NaCl for making calibration solution for pH, drop checker, and TDS meter.
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post #3 of 5 (permalink) Old 06-30-2015, 10:45 PM
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It's been a few years since my undergrad Quant course (one of the reasons why I went for organic synthesis in grad school), but my calculation gave me ~ pH 7.71.

The calculation gets fairly messy because the bicarbonate ion is amphiprotic. However, once you get above a certain concentration of the bicarbonate ion some of the values in the equation are considered negligible. From that point on the pH of a bicarbonate solution will be independent of concentratio (pH of 8.3). With that said, it will most likely be affected by dissolved CO2 in your water sample. How much? It would be hard to tell unless you had a DO meter and some other instruments.

You might get better results out of a calibration solution if you use sodium bisulfate instead. Granted, I'm not sure how readily available that is.

Hopefully someone else with more experience in that area of chemistry will be able to help out.

Do you have a pH meter available? If so, what is your pH reading for a 1 mg / L solution of sodium bicarbonate?
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post #4 of 5 (permalink) Old 06-30-2015, 11:16 PM Thread Starter
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Thanks, I'll give up on pH solutions. It sounds like pre-made pH calibration solution is an easier solution. I hear Borax can be used.
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post #5 of 5 (permalink) Old 07-01-2015, 12:13 AM
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Quote:
Originally Posted by mistergreen View Post
Thanks, I'll give up on pH solutions. It sounds like pre-made pH calibration solution is an easier solution. I hear Borax can be used.
Pre-made will probably give you less headaches, although the sodium bicarbonate could work reasonably if you're just using it to ensure pH meter functionality.

The borax buffer is good to use to ensure that your pH meter / probe is working properly. If I recall correctly, its typical buffer range is around pH 9. Ideally, you'd want a buffer as close to the pH your wanting to look at, but +/- a couple pH units isn't the end of the world.

Just be sure that you have a buffer to bracket either side of your testing range to ensure that the pH meter / probe is functioning properly across that given range.
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