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Chemistry (including Biochemistry)/Adjusting pH of chemical tank


I need to adjust the pH of a Brulin 815GD chemical tank where I work.  The current knowns are the pH and volume.  Currently, the tank is at a pH of 9.5 and I need to raise it to 10.5.  The volume of the tank is 4ft x 7ft x 5ft or 140ft^3, which is equivalent to 3,964.36 Liters.  I will be using NaOH pellets, which I understand to have a molecular weight of 40g/mol, therefore making a 1 molar solution if 40 grams are dissolved in 1 liter of DI water.  I am familiar with chemistry but shakey on the proper equations.  If you could provide the correct equations or direct my understanding in the right direction I am happy to work through this problem myself.  Thank you for your time.

No problem Josh.

Here is a great walk through of the basics:

Read that first, then come back to this:

When you have a pH of 9.5 to start, you are actually saying that you have a specific molarity of H ions:

pH = log [H] = 9.5

With a little algebra you arrive at this:

[H] = 10^(-9.5) = 3.16 * 10^(-10)

This is more H than you want, so lets see where you need to be...

pH = log [H] = 10.5 & then [H] = 10^(-10.5) = 3.16 * 10^(-11)

This makes sense as pH is a log scale and changing the pH by 1 should mean that things change by an order of magnitude.

Now, for your dilemma, the key is neutralize the extra H with OH.  While not 100% of your OH added will find an H, most will.  So, lets see how much we need:

(3.16 * 10^(-10)) - (3.16 * 10^(-11)) =   2.85 * 10^(-10) moles of OH needed per liter

Given that you have ~4000 L, you really should add a minimum of 4000 * 2.85 * 10^(-10)...
or 1.14 * 10^(-6) moles of OH to the tank.  

This should get you in the ball park of pH 10.5.

For several pages on pH:

Take care!

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Dr. Jeffery Raymond


Materials chemistry. Materials science. Spectroscopy. Polymer science. Physical Chemistry. General Physics. Technical writing. General Applied Mathematics. Nanomaterials. Optoelectronic Behavior. Science Policy.


Teaching: General Inorganic Chemistry I & II, Organic Chemistry I & II, Physical Chemistry I, Polymeric Materials, General Physics I, Calculus I & II
My prior experience includes the United States Army and three years as a development chemist in industry. Currently I am the Assistant Director of the Laboratory for Synthetic Biological Interactions. All told, 13 years of experience in research, development and science education.

Texas A&M University, American Chemical Society, POLY-ACS, SPIE

Journal of the American Chemical Society, Nanoletters, Journal of Physical Chemistry C, Journal of Physical Chemistry Letters, Ultramicroscopy Proceedings of SPIE, Proceedings of MRS, Polymer News, Chemical and Engineering News, Nano Letters, Small,, Angewandte

PhD Macromolecular Science and Engineering (Photophysics/Nanomaterials Concentration), MS Materials Science, BS Chemistry and Physics, Graduate Certificate in Science Policy, AAS Chemical Technology, AAS Engineering Technology

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