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How do I know if it is electronic grade sulfuric acid?

2006

I just dug my 5 gal pail of sulfuric acid out of storage in preparation for mixing a new batch of electrolyte for my type II anodizing line. Reading the label on the H2S04 container, I can't see any indication that it is "electronic grade". It simply reads 66 baumé H2S04. Is this the same thing as electronic grade? My gut tells me no. Reading up on the subject a little bit, I came across an article which indicated that if the H2S04 has a slight brown tint to it, that it is loaded with iron and therefore, not electronic grade. From there, I poured some into a beaker and sure enough it has a very pale brown hue to it.

Should I risk it or should I play it safe and purchase a new pail of "electronic grade" 66 baumé H2S04?

If a person were to utilize a lesser grade H2S04, what might the repercussions be?

Thanks again all for your help.
- Cheers!

Daniel DeGueldre
anodizing shop entrepreneur - Ste. Anne, Manitoba, Canada

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First of two simultaneous responses --

66 baumé sulfuric acid is only 93%.Most concentrated sulfuric acid is 98%, so if you want to use a weaker acid, you will need to take account of it in the dilution. Your comment about it having a brown hue is interesting. Pure sulfuric acid should be clear, so it is obviously contaminated. I therefore suggest you safely dispose of it and get some proper acid. You refer to a 5 gal pail - is the pail metal or plastic? If it is metal and unless it is lead lined, you may well have a problem with metal dissolution in the acid.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2006

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Second of two simultaneous responses --

IF brown, it is not clean enough, do not use !

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2006

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Thanks for the help. I wouldn't call it brown, if anything it is a very, very pale straw color (but just barely). It isn't colorless like a glass of water is. It is in a plastic container and in fact the same container that it was purchased in from my chemical supplier.

Looks like I'll be purchasing new, clean acid. Thanks so much for the help! No doubt you folks have saved me alot of time and money!

Thats, that!
Cheers!

Daniel DeGueldre
anodizing shop entrepreneur - Ste. Anne, Manitoba, Canada
2006

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It may not apply to Canada but "Electronic Grade" in UK is a certified purity intended for the semiconductor industry. It is a higher grade then "Analar" certified analytical grade and far more pure than required for conventional anodising. It is also extremely expensive.
Any acid which looks brown is at the other end of the purity (or impurity) spectrum.

Geoff Smith
Hampshire, England
2006