Undstand Difference Between Total Alkalinity And Ph

[freedda]

This is slightly off topic, but I Wasn't sure where else to post this.

I have batch of water mixed with soda ash, which I assume is very high PH. I'm going to add vinegar to it to change this so I can dispose of it in my septic system, and bought pool chemistry test strips to test this, trying to get to a neutral PH.

The test strip test for both Total Alkalinity and for PH. I always thought that testing for PH is a test for level of Alkalinity (to Acid), so testing for both seems redundant to me. So if I want to neutralize this mixture, should I look at the Total Alkalinity or at the Ph level? And in laymen's terms, what is the difference?

Best, David.

[chem geek]

This is slightly off topic, but I Wasn't sure where else to post this.

I have batch of water mixed with soda ash, which I assume is very high PH. I'm going to add vinegar to it to change this so I can dispose of it in my septic system, and bought pool chemistry test strips to test this, trying to get to a neutral PH.

The test strip test for both Total Alkalinity and for PH. I always thought that testing for PH is a test for level of Alkalinity (to Acid), so testing for both seems redundant to me. So if I want to neutralize this mixture, should I look at the Total Alkalinity or at the Ph level? And in laymen's terms, what is the difference?

Best, David.

David,

pH and Total Alkalinity (TA) are measuring different things, though they are related in the sense that the amount that pH will move from adding an acid is inversely related to the TA level. The easiest way to know how much acid it will take to neutralize a solution is to use an acid demand test. Such a test (as well as a base demand test) is found in the Taylor K-2006 (or K-2005) test kit which you can get at a good online price here. Vinegar, by the way, is usually very dilute so is not a particularly good acid to use unless you plan on using a lot of it. To neutralize something that has a lot of soda ash in it, adding a stronger acid such as Muriatic Acid you can get at a hardware store or dry acid (sodium bisulfate) you can get at a pool or spa store would be better.

pH is a logarithmic measure (that is, every 1 unit change is a factor of 10) of the concentration of hydrogen ion and that determines the acidity of the solution (acidic if pH < 7). In the opposite direction away from neutrality, at pH > 7, the solution is basic aka alkaline which would be the case for your solution with soda ash. TA is a measure of any chemical species that can accept hydrogen ions so if the TA is high such species combine with the hydrogen that is added from acids such that the effect on pH is far less. Soda ash not only increases pH, but it also increases TA a lot as well. This basically means that though the pH may be measured as high from the Soda Ash, you can't tell how much acid you need to add just from the pH -- you need to know the TA or more easily use the acid demand test as indicated above.

If you know how much soda ash you added to something that was pretty close to neutral, you can estimate how much acid it will take to neutralize it. 1 ounce weight of Soda Ash is neutralized by about 1 fluid ounce of full-strength Muriatic Acid (31.45% Hydrochloric Acid) or 1.4 ounces weight of Dry Acid (93.2% Sodium Bisulfate). You can then retest the pH after adding such acid and mixing and then see if you're close enough to neutral for your septic tank.

Richard

[freedda]

thanks chem geek.

I tried adding vinegar, since I had it around. I did lower the pH, but not by much, and it also bubbled up, sort of like a chemistry set volcano I made when I was a kid (except that one was baking soda, not soda ash). I wonder if the other acids you mentioned will also make it bubble up?

Best, David

[chem geek]

Yes, other acids would likely cause the bubbling as well. Basically, when the acid is somewhat concentrated and hits an area that is high in soda ash concentration, it produces carbon dioxide bubbles just like a carbonated beverage. The same thing would happen if you added vinegar to baking soda (that's something many kids do at home -- careful: it makes a mess from all the bubbling). The fact that you created bubbles probably means that the amount of soda ash is fairly high so a stronger acid would be needed so that you don't need to add so much.

[AquaclearNZ]

thanks chem geek.

I tried adding vinegar, since I had it around. I did lower the pH, but not by much, and it also bubbled up, sort of like a chemistry set volcano I made when I was a kid (except that one was baking soda, not soda ash). I wonder if the other acids you mentioned will also make it bubble up?

Best, David

Congratulations - you just re-created your high school experiment

Alkalinity level in a swimming pool is a meausre of alkaline materials in the pools water, and is also offten referred to as buffer, as it acts as a buffer against change in pH

To increase the alkalinity level - you add sodium bi-carbonate - the common household name for this product is baking soda

Use a muriatic acid, or sudium bi-sulphate to reduce the pH safely