Sulfuric acid percentage values and sodium bisulfate alternative?

What About Bob · Jun 5, 2025

I have scoured all around the forums and the web for any answers as to what the conversion would be to find percentage values for sulfuric acid. I always see sulfuric acid values in moles, "N" and other values. One exception that I have seen percentages are for the battery acid versions, 37%, 30%, etc. I have the math for breaking this down further to reach a 10% solution which will be added to a potassium permanganate bleach solution, per Ilford's instructions, but a part of me would prefer to try out sodium bisulfate instead. Amazon has the battery acid version that shows the percentage values but you have to buy like eight containers of the stuffI and I really don't want to stock sulfuric acid in big amounts which is why I was thinking to use the bisulfate instead.

So a question I would have is how would I determine the amount of bisulfate to use instead of a 10% solution of sulfuric acid?

I did read over a past post by Gerald who gave the math on the substitution but it was done in moles and not percentages. If anyone would have any directions where I could go to determine the values that would be great. Thanks.

Raghu Kuvempunagar · Jun 5, 2025

You need to use 4.42 g of Sodium Bisulphate (anhydrous) for every ml of concentrated Sulphuric Acid. So, if Ilford is recommending you to use 10 ml of concentrated Sulphuric Acid, then use 44.2 g of Bisulphate. But no harm will be done if you instead use 45 g if that's easier to weigh.

What About Bob · Jun 5, 2025

Raghu Kuvempunagar said:
You need to use 4.42 g of Sodium Bisulphate (anhydrous) for every ml of concentrated Sulphuric Acid. So, if Ilford is recommending you to use 10 ml of concentrated Sulphuric Acid, then use 44.2 g of Bisulphate. But no harm will be done if you instead use 45 g if that's easier to weigh.

Thanks Raghu

My new gram scale measures out to two decimal places. Oddly It didn't come with a calibration weight so I have to hunt one down. All my other scales came with them.

ags2mikon · Jun 5, 2025

You can buy the battery acid from your NAPA or other auto parts stores in smaller sizes. I bought mine from O'Reilly auto parts for motorcycle batteries.

What About Bob · Jun 5, 2025

ags2mikon said:
You can buy the battery acid from your NAPA or other auto parts stores in smaller sizes. I bought mine from O'Reilly auto parts for motorcycle batteries.

Thanks ags2mikon

I was pointed to a local AutoZone. I had to go to the MSDS sheet for extra information. The percentages listed in the sheet for this acid is 30-43%. It is by East Penn. I'm guessing it can be any one of those values. Would it be safe to say I can go in the middle and use 37% as original chemical value for the calculation?

I'm using: (percentage required for solution * total volume of solution / percentage of original chemical).

ags2mikon · Jun 5, 2025

Generally 30-32% for lead acid batteries. IIRC. I think I marked mine as 31%. I'm not near my darkroom now. Dilute by pouring the acid into the water not the other way. Gloves, face shield and appropriate PPE is in order. It is safe if you use caution, just like driving.

koraks · Jun 6, 2025

AFAIK the acidity of a permanganate bleach is not critical. For bleaches like these, I've always just used 'a dash' of something.

Donald Qualls · Jun 6, 2025

You can also buy concentrated sulfuric acid at home improvement stores, sold as a drain cleaner/opener. I have a bottle at home, purchased to make bleach for B&W reversal. It'll probably cost less for a pint-ish bottle than buying a box of battery acid sized for filling a dry charged car battery (if NAPA will even still sell theirs).

koraks · Jun 6, 2025

Donald Qualls said:
You can also buy concentrated sulfuric acid at home improvement stores, sold as a drain cleaner/opener.

Check the bottle before purchasing; the constituents of drain cleaner differ wildly across the globe and potentially with in the US as well. Around here, drain cleaner is virtually always sodium hydroxide.

Donald Qualls · Jun 6, 2025

koraks said:
Check the bottle before purchasing; the constituents of drain cleaner differ wildly across the globe and potentially with in the US as well. Around here, drain cleaner is virtually always sodium hydroxide.

At my local Lowe's the drain openers that aren't (pure or impure) sodium hydroxide are stored separately and they have enough SDS-type information to know what I'm buying. I used to get Red Devil Lye at the supermarket, but now I have to order a generic brand from Amazon.

What About Bob · Jun 9, 2025

I am seeing a product called liquid lightening drain cleaner at Walmart's site. Maybe the local Walmart would have it. Says 44.25% by weight. It also states not to use it on stainless steel? My guess is that an SS tank should be alright with this when the acid is further diluted? Going down to 10% working solution. Should I store the 10% working solution in a glass container or a regular old photo bottle? I have never dealt with sulfuric acid before but am educating myself on the safety of it. Thanks.

Rudeofus · Jun 9, 2025

What About Bob said:
I am seeing a product called liquid lightening drain cleaner at Walmart's site. Maybe the local Walmart would have it. Says 44.25% by weight. It also states not to use it on stainless steel? My guess is that an SS tank should be alright with this when the acid is further diluted? Going down to 10% working solution. Should I store the 10% working solution in a glass container or a regular old photo bottle? I have never dealt with sulfuric acid before but am educating myself on the safety of it. Thanks.

Glass bottles should work for Sulfuric Acid of all concentrations. If you want to switch to plastic bottle, there are some which can handle low pH and others can't. Don't buy or use random bottles for this. If the dealer "doesn't know for sure", then do yourself a favor and search elsewhere. A Sulfuric Acid spill will always be more expensive than any chem bottle you can buy anywhere.

The best bottle for storing chems is typically the bottle they come in, since someone knowledgeable must have already done all the research ...

Donald Qualls · Jun 9, 2025

I'd avoid that 44% acid, you can get concentrated at Lowe's and have easier math for dilutions...

lamerko · Jun 9, 2025

Donald Qualls said:
I'd avoid that 44% acid, you can get concentrated at Lowe's and have easier math for dilutions...

But also more dangerous...

Donald Qualls · Jun 9, 2025

lamerko said:
But also more dangerous...

A little more so. I wouldn't want to spill either one on a wood floor, or my skin.

Rudeofus · Jun 9, 2025

Donald Qualls said:
A little more so. I wouldn't want to spill either one on a wood floor, or my skin.

The issue is not only direct hit by Sulfuric Acid, but also by the crazy reaction of concentrated Sulfuric Acid with little drops of water falling in. I asked my local chems dealer "What's the highest concentration you'd give a doofus like me comfortably?", and they gave me 15%. Of course you can easily buy battery acid, which is more than twice as concentrated, but you'd ask yourself about the risks. Is it really worth the risk of having such concentrated stuff in your dark room, if you have fun (and a few beers) with analog buddies in this same place?

So I guess the answer to "which concentration should I get?" depends a lot on your dark room and personal life style choices.

What About Bob · Jun 9, 2025

I was at Walmart today and they had the stuff but I felt kind of squeamish about it, lol, so I left the store without it.

Rudeofus said:
The best bottle for storing chems is typically the bottle they come in, since someone knowledgeable must have already done all the research ...

If I did get it I was thinking of not bothering with making up a 10% solution to store and instead use a pipette to draw out the stuff from the original container then close it back up, put it back in the ziplok baggie it came in and put it away. Less handling Wearing gloves and safety goggle of course.

For now I think I will stick with the sodium bisulfate.

Rudeofus · Jun 9, 2025

What About Bob said:
I was at Walmart today and they had the stuff but I felt kind of squeamish about it, lol, so I left the store without it.

I know, it's a bit late now for that, but Sulfuric Acid concentrations seem to be given as weight/weight. This means 1kg of 37% Sulfuric Acid is 370 grams pure H2SO4 and 630 grams water.There are fancy tables out there to get density from temperature and weight/weight concentration, so you can easily calculate the amount of H2SO4 per liter. Using this table 1 liter of 37% H2SO4 at 20°C/68°F would weigh 1.2769 kg and therefore contain 472 gram pure H2SO4 and 804 grams water.

What About Bob said:
If I did get it I was thinking of not bothering with making up a 10% solution to store and instead use a pipette to draw out the stuff from the original container then close it back up, put it back in the ziplok baggie it came in and put it away. Less handling Wearing gloves and safety goggle of course.

In my experience 15% Sulfuric Acid is pretty mundane unless you get it in your eyes (don't !!!!! ). It will not jump in your face, even if a droplet of water falls in. You can wash it off your skin. Our skin is more resistant to acids than to alkalis, so Rodinal concentrate is likely more hazardous than 15% sulfuric. As far as handling, there are two critical you should look at:

the bottle opening: I have several bottles, which if I pour these slowly and carefully, then chems would be running down the bottle instead of pouring into the container. There are special bottle inserts to prevent this, and you should try to get these and use them.
secondary containment. A zip lock bag is IMHO not the optimal solution, since how would you handle the situation with chemistry spilling inside that bottle? Rather get a few developer trays (of which we assume they can handle acid and alkali) to store compatible bottles. General rule is, that the secondary containment should be easily able to handle total breakdown of the largest chem container stored in it.

What About Bob said:
For now I think I will stick with the sodium bisulfate.

Bisulfate will work well for anything at pH >= 2, which covers most photographic solutions you'll ever encounter. Ilfochrome dye bleach was one exception, but this was discontinued over a decade ago.

Donald Qualls · Jun 10, 2025

Rudeofus said:
if you have fun (and a few beers) with analog buddies in this same place?

If you have "a few beers" in the darkroom violates everything I learned about chemical safety in high school and college. If you bring buddies and beer into the darkroom, you shouldn't have developers, fixer, or heaven forbid stop bath concentrate in there -- which badly limits its functionality as a darkroom. Or at the very least, all chemicals should be in a locked cabinet when there's a party mentality in the darkroom.

koraks · Jun 10, 2025

Donald Qualls said:
If you bring buddies and beer into the darkroom, you shouldn't have developers, fixer, or heaven forbid stop bath concentrate in there -- which badly limits its functionality as a darkroom.

Are you concerned that buddies will break into the stop bath concentrate once the beer runs out? Come on, let's not overreact. IDK about @Rudeofus' darkroom, but mine is in our home and I occasionally have friends over and/or have a glass of wine there. So far, everyone has managed to not drink the used fixer. I also think there's a difference between a couple of guys having a few beers and a "party mentality." Do you take the chlorine bleach, drain cleaner and root killer out of the cabinet and lock it up in a safe whenever you expect guests? I admit that I don't. Again, so far, so good - nobody has mistaken the yellow bottle of bleach for lemonade, yet.

ags2mikon · Jun 10, 2025

I have a coffee maker, and a refrigerator that has bottled water, cokes, beer and wine in it and some chocolates. I don't touch any of it without washing my hands first, and I don't take them into the wet end, where the chemicals are kept. Different moods require different "things".

MattKing · Jun 10, 2025

Perhaps you need a three sided darkroom - the dry side, the wet side, and the buddies and beer side.

But yes, if you use a darkroom for many purposes, you need to "develop" some special protocols to keep things safe.
That is what I do in the kitchen that I also use for film development.

darkroommike · Jun 11, 2025

What About Bob said:
Thanks Raghu

My new gram scale measures out to two decimal places. Oddly It didn't come with a calibration weight so I have to hunt one down. All my other scales came with them.

Are you in the USA? A new US 5 cent coin, aka a nickel, weighs exactly 5 grams. If not check on mint coin weights where you live. Coinage tends to be very accurate.

Donald Qualls · Jun 11, 2025

darkroommike said:
Coinage tends to be very accurate.

But if you use a US cent (aka penny), be sure it's new and look up the correct weight -- they changed from copper/nickel (3.1 gram when new) to copper plated zinc (2.?? g) in 1982. Weight may have changed again when they removed the Lincoln Memorial in 2009 (but probably didn't).

What About Bob · Jun 11, 2025

darkroommike said:
Are you in the USA? A new US 5 cent coin, aka a nickel, weighs exactly 5 grams. If not check on mint coin weights where you live. Coinage tends to be very accurate.

Thanks, darkroommike and Donald

On my old scale the nickel measures 5 grams exactly though on my new one it measures 4.96 grams. The nickel isn't new. This new scale does a double calibration. It first requests the 100 gram weight and then the 200 gram weight before it will go to the PASS indicator. I haven't had a scale that calibrated like that before.

Sulfuric acid percentage values and sodium bisulfate alternative?

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