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Converting percent by volume to oz/gal HN03


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July 30, 2021 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I am trying to compare out shop process control limits, which we list in weight percent, with limits in the Metal Finishing Guidebook which list the concentration for acid pickling and etch solutions in terms of percent by volume (v/v). I am struggling to understand how the percent by volume for acids is calculated. Is it assumed that you begin with some standard stock concentration for each acid?

Brooke Nahring
- Bremerton WA

August 9, 2021

A. Brooke,
That is generally the case, although also generally the recipe or standard will describe the stock solutions in terms of weight percent or specific gravity or some such.

Some acids in their "pure" form are anhydrous powders, while others are essentially never available outside of aqueous solution.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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Closely related historical postings, oldest first:


Q. We are in the process of revising all of our internal titration procedures and we came up with a question that we cannot seem to come up with a solution for -- we hope you have an easy answer for us. Per our Spec. it calls out for 20-25 % by volume of HN03 and a concentration of 27-33 oz/gal. What is the conversion factor we should use after titration to convert the percent by volume to oz/gal. in this case? Your input would be very appreciated.

Thank You,

Steven Rij
Plating Shop - Salt Lake, Utah, USA

simultaneous 2004

A. Based on your question I suspect you may find it very hard to understand and work with titrations and other lab procedures. You should know by now, but one US gallon has 128 fluid ounces. So, a concentration of 25% (1/4) by volume means 128/4 = 32 ounces per gal., whereas 20% (1/5) means 128/5 = 25.6 oz/gal. This is for two liquid substances mixing together. If one of them is solid, then the ounce represents mass not volume and the ratio is different.

Guillermo Marrufo
Monterrey, NL, Mexico


A. One gallon contains 128 Oz. 25% is 1/4. So you want 1/4 of the gallon to be HNO3. Divide 128 by 4 to give an answer of 32 Ozs. 20% is 1/5, but dividing 128 by 5 is the hard way. Instead, multiply 128 by 0.2, which gives 25.6 Ozs. The first example could have also been done by multiplying 128 by 0.25. Just a matter of which method is easier.

Tom Gallant
- Long Beach, California, USA

December 4, 2012

Q. Converting percent by volume to oz/gal NaOH.
We have just added a new cleaning tank and I need a conversion formula as the titration I am using is stated in oz/gal.
Our tank is 20 gallons at 5%.
Thank you for your help.

Connie Rancourt
- Brattleboro, Vermont, USA

simultaneous December 5, 2012

A. NaOH is a solid and not a liquid, so I see no way it can be made up by volume.

You probably use 50% caustic soda solution, which contains 6.25 pounds or 100 oz/gallon of NaOH. A 5% by volume solution of this would contain 5 oz/gal of NaOH.

Chris Owen
- Nevada, Missouri, USA

December 5, 2012

A. Connie, in what form is the NaOH? Solid, 50% in water, or what?

James Totter
James Totter, CEF
- Tallahassee, Florida

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