Sodium Bicarbonate Analysis

Standard Methods for the Examination of Water and Wastewater
AWWA

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A. Bicarbonate is a funny beast.

There is an equilibrium between dissolved, un-ionized CO2, bicarbonate ion, and carbonate ion. It depends on pH, TDS, and temperature - mostly pH. Carbonate buffering is largely responsible for maintaining the constant pH of 7.4 in our bodily fluids.

If I were you: I'd look at
<== 'Standard Methods ...'. There is a fairly involved discussion of carbonate solution chemistry. A careful, accurate pH measurement + two titrations with 1.0 N HCl (one to a methyl orange ⇦ this on eBay or Amazon [affil links] endpoint - one to a phenolphthalein endpoint) will likely give you all the information you need to get a pretty accurate answer.

Depending on the matrix, you might get a better result using a titrimetric determination of carbonate (see "The Handbook of Metal Finishing") plus a pH determination.

Without more info on the kind of bath you're trying to test, it's tough to be more helpful.

A. Cindy,

I usually deal with carbonate not bi carbonate so I looked up a procedure. It is as follows:

1. Prepare sample as a 0.1N solution of bicarbonate in a stoppered volumetric flask without allowing the temperature to rise.

2. Take 25 ml of the above solution and add 30 ml of 0.1N alkali (carbonate free) and 10 ml of a 10% solution of barium chloride.

3. Titrate back to phenolphtalein with 0.1N acid. Also titrate a blank solution containing the same amount of alkali and barium chloride. The difference represents bicarbonate, each ml of solution corresponding to 8.4 mg of the sodium salt.

The above is from
<== 'Volumetric Analysis II' by Kolthoff and Stenger. I feel that a few bits of information were left out. First the 25 ml of the 0.1N sodium bicarbonate solution you remove should be by Mohr pipette [pipettes on eBay or Amazon [affil links] into a flask.
Second, the instructions a basically giving you the method which you then have to calculate against.

Different methods of analysis may be indicated depending upon what other chemistry is present in the solution to be analyzed.