Letter 5032

Sulfuric Acid Percentage 

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Just a quick question on figuring out the percentage of Sulfuric acid in my anodizing tank. I know that 165gr/litre is equivelent 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 132gr/liter? Thank you for any help.

Marc Green anodizer - Boise, ID, USA

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 precide 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
- Sulmona, Italy

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, OH

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 or Lange's Handbook. It has a wealth of useful tables of specific gravity for mos 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, WA

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