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Re: Here comes the anal engineer...

Posted By: Wintek <wintek@aol.com>
Date: Friday, 30 July 1999, at 8:26 p.m.

In Response To: Re: High PH problem (Alistair)

Hello Alistair

Forgive me for being picky!

pH=-log[H+], like you said. But, only if there are no other pH altering chemicals present can the [H+] be derived from the Henderson Hassblach equation and the equilibrium constants for the carbonate buffering systems. This plays havoc in my tank where there is phosphate introduced from the tap water, or in plant tanks were OH- is produced during biogenic decalcification. To make things really uncertain, the equiibrium constants change (oxymoron?!!) with temperature and TDS levels.

When we test for buffering capacity, it's done by measuring alkalinity and labelling it carbonate hardness (KH) because the *assumption* is that what is providing the buffering capacity are the bicarbonate and carbonate ions. When we test for GH, we measure the combined concentrations of [Ca++] and [Mg++], and then *assume* all of it is from calcium, and convert the titration data accordigly. Have I made this even worse than it allready is?

The pH of pure water exposed to atmospheric CO2 is below six. I haven't the ability to measure lower, but somewhere 4.8 foggily comes to mind from chemistry class, but that's probably saturated CO2 (carbonic acid, H2CO3)

What buffer are you looking for?

Wintek


 

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