book Water, palmer - figure 13

[rodrigoschuch]

Hello folks!

I have a question about water:

This is my water profile:

Ca: 3.6 ppm
Mg: 2.7 ppm
Na: 6 ppM
Chloride: 9.2 ppm
Sulfate: 13.4 ppm

Bicarbonate: 22 ppm
Total alkanility: 19.3 ppm as Caco3
Ph: 6.4

My question: In the palmer water book, there is a figure (n 13) showing the percentage of carbonate species according to the ph .. and at pH 6.4 we have approximately 51% bicarbonate and 49% carbonic acid.

I know that having the parameters of alkalinity and pH, it is possible to estimate the amount of bicarbonate. But how can I interpret these propotions?

 

[ajdelange]

This is explained in some detail at https://www.homebrewtalk.com/showthread.php?t=473408. The proportions you refer to are f0, f1 and f2 in that post. Have a look there and see if it answers your question. If not come back here.

 

[rodrigoschuch]

This is explained in some detail at https://www.homebrewtalk.com/showthread.php?t=473408. The proportions you refer to are f0, f1 and f2 in that post. Have a look there and see if it answers your question. If not come back here.

I think my confusion is about that paragraph

Is this relationship made by Palmer right?

There is the bicarbonate and the pH value. However, this is confusing... because considering 22 ppm of bicarbonate and pH 6.4, this value would be 51% of total alkalinity

Does it make any sense?

 

[ajdelange]

I think my confusion is about that paragraph

Is this relationship made by Palmer right?

I'm not sure which paragraph is the confusing one but no, the paragraph in the image you posted is not correct. At pH 7 about 80% of the carbo species (species containing carbon and oxygen i.e. carbonic acid, bicarbonate ion and carbonate ion) are in the form or bicarbonate but the remaining 20% is in the form of carbonic acid and virtually none is in the form of carbonate ion. As such carbonate ion does not contribute anything to the alkalinity. Carbonic acid does not contribute anything to alkalinity either as it cannot absorb any more protons. Thus, at pH 7, virtually all the alkalinity is from the bicarbonate ion.

There is the bicarbonate and the pH value. However, this is confusing... because considering 22 ppm of bicarbonate and pH 6.4, this value would be 51% of total alkalinity

No, bicarbonate ion would be 51% of the total carbo content in the water but it would be the sole source of alkalinity (except for the very slight contribution of the water itself.

Does it make any sense?

If you take the reported bicarbonate content of 22 mg/L and divide it by the equivalent weight of bicarbonate ion which is 61 you get 0.36 mEq/L bicarbonate and as this is the only source of alkalinity, except the water, the bicarbonate alkalinity is 0.36 mEq/L. Multiplying this by 50 gives you a bicarbonate alkalinity of 18 ppm as CaCO3. Adding 1 - 2 (depends on the pH used as an end point for the titration)ppm as CaCO3 for the water itself we have a total alkalinity of 19 - 20 which is consistent with your report.

Remember that the lab measured alkalinity, not bicarbonate, so that is where you should start. If you follow the procedure in the sticky I referenced you should get, from the reported alkalinity, a bicarbonate number close to 22 mg/L. You will calculate f0, f1 and f2 (the relative fractions) but not use them directly. You will, instead, calculate the charge on a mole of carbo, f1 + 2*f2 ~ f1 (because f2 will be so small). You yes, it all makes sense even though the book does not perhaps present the clearest explanation (and does, in this appendix, contain an error).

 

[rodrigoschuch]

Now things make sense! Thank you!

All my confusion was about the first one..
I was in doubt if it was my mistake of interpretation
And the fact that carbonic acid does not contribute to alkalinity!