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"Determining Sulfuric Acid Percentage in Anodizing Tank"


Q. Just a quick question on figuring out the percentage of Sulfuric acid in my anodizing tank. I know that 165 gr/litre is equivalent to a 15% bath. If you do the math 165/15...you come up with 11. Can I use 11 as a factor when figuring out my percentage? i.e. a 12% bath would be 132 gr/liter? Thank you for any help.

Marc Green
Marc Green
anodizer - Boise, Idaho


A. Marc,

If your solution 15% (weight/weight) corresponds to 165 g/l, it means that density is 1.1 g/cc (your 11, because to have g/l, you multiply also by 10), but a lower percentage as 12% has got for sure also a lower density due to the lower sulphuric acid content.

So you have to multiply % value by density (measured for instance weighing 100 cc of solution on a precise balance: if 100 are 108 g, the density is 1.08 g/cc).Don't forget that pure sulphuric (96-98%) has a density of 1.84 g/cc. Example: 12 * 1.08 * 10 = 129.6 g/l. I hope to read you again.

Francesco Cicchetti
Francesco Cicchetti
- Sulmona, Italy


A. Sounds logical to me, but I'd take and obviously make up several different % baths and test your theory, but really, math is math, and that seems to be a logical way to start. How accurate it may be is questionable, but there is always a few % difference in this stuff anyway, just trust your instincts

Matthew Stiltner
- Toledo, Ohio


A. Marc:

I don't think the conversion factor holds true. My source is the Chemical Rubber Company Handbook of Chemistry and Physics 50th Edition, 1963 (I am an old guy!). 12 % is 129.6 g/l. At 20 %, it is 227.9 and at 30%, it is 365.6 g/l.

Your best bet is to purchase a "CRC Handbook of Chemistry & Physics" [affil. link to book on Amazon] or "Lange's Handbook of Chemistry" [affil. link to book on Amazon]. It has a wealth of useful tables of specific gravity for most common solutions along with % stated in g/l and lbs/gal. Both books also give you invaluable information on reagent makeup for analytical work, conversion from metric to English units and a full section of mathematical expressions not easily found.

I have had my CRC since high school. I used it through my undergraduate work and all my working career. Chuck Reichert

Charles R. Reichert CEF-SE
- Seattle, Washington

February 13, 2013

Q. I am dealing with hard anodising, I want have to calculate the concentration of sulfuric acid bath through quantitive analysis, so I want to know the detail procedure for this.

Aijazullah Tajir
- Abu Dhabi, UAE

May 19, 2016

A. You can use this formula to get a more exact answer for H2SO4 (g/l) Concentration as a function of Pwt(%)

Concentration(g/l) = Qf * SG(H2SO4) * D(H2O)

Qf = [330.9(Pwt^3)+92.3(Pwt^2)+572.6(Pwt)]/1000

SG = 1.84 :Specific Gravity
D = 1000 g/l :Density
Qf= formula :Conversion Factor
Pwt = 0-1 : Percent Wt of H2SO4 12% = .12

For Pwt = 12%

Qf= [330.9*.12^3 + 92.3*.12^2 + 572.6*.12]/1000
Qf= [70.6129]/1000 = 0.0706129

Concentration(g/l) = [0.0706129]*1.84 *1000 g/l
Con = 129.93 g/l

This is all derived from the basic formula:

Density(final) =
[Mass(H2SO4) + Mass(H2O)]/[Volume(H2SO4) + Volume(H2O)]

Solving for Final density as a function of SG & Pwt:

Df = D(H2O)/[(Pwt/SG)+(1+Pwt)]

Concentration(g/l) = Df*Pwt

I plugged this formula into Excel and did some
*math magic* to get a trend-line that gives the formula for Qf. (R^2 = 1)

Hopefully this will be useful to someone.

John Kent
- Spotswood, New Jersey, USA

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