Re: [APD] KH question

[Vaughn Hopkins <hoppycalif at yahoo_com>]

Liz, I am relieved to learn that I am still not a chemist!  For a  
moment I was afraid I was one.

VaughnH.

On Nov 19, 2006, at 9:46 PM, Liz Wilhite wrote:

> I know I should let this pass but...
>
> Adding carbonate does buffer the system. A buffer solution contains  
> a weak
> acid and its conjugate base. Carbonate is a base which reacts with  
> water, an
> amphoteric substance, forming bicarbonate ions and clusters of water
> molecules of various numbers and shapes that have hydrogen ions  
> associated
> with them.  The conjugate base of bicarbonate is carbonate. If you add
> bicarbonate to water, it also reacts with water forming carbonate  
> ions and
> those same clusters of water molecules with hydrogen ions.
>
> Adding CO2 to water forms "carbonic acid" which is either an  
> incredibly
> strong acid or a pretty weak acid, depending upon how you define  
> "carbonic
> acid."  The dissolution of CO2 in water yields a solution  
> containing water
> molecules associated with hydrogen ions, bicarbonate and carbonate  
> ions.
>
> The addition of carbonate (or bicarbonate) ions to water creates a  
> solution
> to which an acid can be added without a large change of pH -- i.e. it
> creates a buffer solution.
>
> I was just looking to know if anyone with a relatively low KH had  
> suffered a
> pH crash as a KH of 3 indicates a reasonably low concentration of  
> carbonate
> and bicarbonate ions in solution, even assuming that there are no  
> other ions
> interfering with the KH test and I'm not certain that is a valid
> assumption.  I appreciate knowing that you haven't had any troubles  
> so I
> shouldn't expect any, either.
>
> On 11/19/06, Vaughn Hopkins <hoppycalif at yahoo_com> wrote:
>>
>> Where I live now my tap water has KH below 1.  I don't add anything
>> to "buffer" it.  I use 40 ppm of CO2 in the tank, and the pH hasn't
>> changed enough to cause either the fish, shrimp or plants to  
>> complain.
>>
>> Incidentally, to buffer a solution requires adding a substance that
>> resists increases in pH and a substance that resists decreases in pH
>> - always two substances.  Adding just one, like bicarbonates, only
>> shifts the pH higher, it does not buffer the solution to a  
>> specific pH.
>>
>> I just felt a need to be pedantic there.  Sorry.
>>
>> VaughnH.
>>
>>
>>>
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