A Vinegaroon Experiment in Progress

[Gosut]

AKA iron liquor. I've wanted to tinker with this since learning of it several week ago. Of particular interest is the chemistry of making ferrous acetate, the stuff that reacts with tannic acid to turn leather black. Unfortunately, I've forgotten most of what little chemistry learned in school, but I wasn't comfortable just winging it. The first question is how much acetic acid is in vinegar, in this case distilled white vinegar. The second is the chemical reaction involved. The third is the amount of iron needed to react with the acetic acid to make ferrous acetate.

Important: Before we start, every bit of what follows could be wrong.

It's been decades since I've been in a chemistry class, and all these calculations could be wrong. I'm hoping that any leatherworkers who know chemistry can comment on all this. In any event, please double check these calculations.

First, the Vinegar

The white vinegar I'm using says it's 5% acidity. But is that 5% by weight or by volume? So far, haven't found a definitive answer. An FDA regulation on vinegar implies that it's by weight; it gives grams of acetic acid to ml of water, and 1 ml of water is essentially 1 gram for the tolerance range of measuring instruments found in the home. So 5% acidity is 0.05 acidity, which should be 5g acetic acid/100ml water. For 1 liter that's 5/100 x 10/10 = 50/1000, so there should be 50g acetic acid to a liter of 5% acidity vinegar.

Next the Chemistry

Acetic acid has a formula of C2H4O2, and a molar mass of 60.052g. Iron is straight Fe, of course, and has an atomic weight of 55.845. The way chemistry is set up, I think that means iron has a molar mass of 55.845g. The reaction of iron to acetic acid is Fe+2(C2H4O2) yields Fe(C2H3O2)2 + H2. So it takes 2 moles of acetic acid to react to 1 mole of iron to yield 1 mole ferrous acetate.

How Much Iron does this Take?

Since it takes two moles of acetic acid to react to one mole iron, the ratio of iron to acetic acid by weight should be 55.845 / 2(60.052) = 55.845/120.104. For a liter of 5% by acidity vinegar, that should be 50 x 55.845/120.104 = 23.248g iron.

Maybe. There's a strong chance all this is wrong. Please double check these calculations.

Now the Experiment

For this, I used a 2 liter soft drink bottle. First I measured the full capacity of the bottle. Since the iron will take up space, I hoped it would be large enough without having to tinker with the calculations. The density of iron is 7.874g/ml, and using 2 liters of vinegar hopefully means that I'll need s x 23.248g iron, which is 46.496g iron. 46.496/7.874 = 5.9ml. So the iron and the vinegar should come to 2005.9 ml. It looked like the bottle would hold it, so I then rinsed it out and bored a small hole in the center of the cap to let out the hydrogen produced by the reaction. Two liters should take 2 x 23.248g iron = 46.496g iron. I set the kitchen scale to grams (unfortunately, it only measures to whole grams), put a paper plate on it, zeroed it out, and weighted out 47g of 0000 steel wool, then bumped it up to 49g, which both used complete bats of the steel wool on hand and gave a little excess iron. Using a funnel, I poured a small bit of iron vinegar in the bottom. Right or wrong, thought this might prevent some air spaces. Then I pulled apart the steel wool as I packed it inside the bottle. Then, with the funnel, I slowly filled the bottle with vinegar to the very top.

Hopefully, in filling the bottle to the top, that minimizes the surface area exposed to oxygen. Had thought about putting just a tad of neatsfoot or mineral oil on top to seal the surface from air, but the bottle was too full.

The plan is to wait at least a week, then pour the liquid into another bottle, using a coffee filter in a funnel as a strainer.

Now we wait.

Now, About that Ferrous Acetate

It has a molar mass of 173.993g, and 2 liters of vinegar may produce 173.993g x 46.496g/55.845g = 144.865g ferrous acetate. I think that means this yields a (144.865g / 2000g water) x 100% = 7.24% solution of ferrous acetate. That's if all this is correct.

[Gosut]

Important update:

This method has produced a miniature geyser. I don't know if it's a change in volume or just hydrogen bubbles coming to the surface, but I'm getting an almost steady flow out the top of the cap down the side of the bottle. In other words, a mess.

Fortunately, I had it outside due to the vinegar odor, and have moved the bottle to something that the vinegar won't harm. It's not something anyone would want in their house or work shop.

Why am I thinking change in volume? Grasping at straws, really. The temperature outside is warmer than inside, and wondering if the steel wool is expanding enough to force s little vinegar out of the hole in the cap.

[Wepster]

this may or may not be helpful... in another craft, it is called ebonizing wood. Here is the first reference I found, search it, it is very popular (since ebony is very expensive!)

https://www.popularwoodworking.com/finishing/ebonizing_wood/

[fredk]

37 minutes ago, Gosut said:

Important update:

This method has produced a miniature geyser. I don't know if it's a change in volume or just hydrogen bubbles coming to the surface, but I'm getting an almost steady flow out the top of the cap down the side of the bottle. In other words, a mess.

Fortunately, I had it outside due to the vinegar odor, and have moved the bottle to something that the vinegar won't harm. It's not something anyone would want in their house or work shop.

Why am I thinking change in volume? Grasping at straws, really. The temperature outside is warmer than inside, and wondering if the steel wool is expanding enough to force s little vinegar out of the hole in the cap.

Did you punch air holes in the jar lid?

[Gosut]

2 hours ago, fredk said:

Did you punch air holes in the jar lid?

Bored a hole in the center of the bottle cap. It's in a plastic 2 liter soft drink bottle. Here seems to lie some of the difficulty. I was after limiting the surface area to the air. What seems to have happened is a wad  of steel wool has collected enough hydrogen to float, in the process acting as a plunger pushing vinegar up out of the cap. Unfortunately that, and the accumulated hydrogen, has pushed out enough to leave some steel wool at the neck exposed. Have topped it off with more vinegar, which isn't ideal for this, experiment-wise. I don't know how much iron acetate I've possibly lost. True, it's likely to be slight, but it may also leave the solution with surplus vinegar. May have to scrounge up a plastic rod to push the steel wool back down.

This is surprising in that I shredded the steel wool pretty well before putting it in the bottle. Putting it through the neck of the bottle may have compressed it enough that it can give the plunger effect.

Have checked the bottle for leaks and found none.

It looks like rain could be heading this way, and have put it under a roof, in a plastic flying disk with some folded paper towels.

[Gosut]

3 hours ago, Wepster said:

this may or may not be helpful... in another craft, it is called ebonizing wood. Here is the first reference I found, search it, it is very popular (since ebony is very expensive!)

https://www.popularwoodworking.com/finishing/ebonizing_wood/

Thanks. I'll look into it. 

[Gosut]

Update: Though there was only a small bit of vinegar on the cap, I didn't like the way the steel wool was bulged up, with gas pockets visible against the side of the bottle. I took a plastic drinking straw, which wouldn't displace that much vinegar, and pressed it down, releasing gas.

Most of what came up has to have been trapped air. Although I have seen some bubbles form on the steel wool, there's been no noticeable amount dissolved. That means that even though I'd shredded the steel wool, it was compressed enough to hold air.  Once again, I think passing it through the bottleneck lead to this. Using a bottle, I'd have to tear it apart even finer and not pack so much through at one time.

Temperatures are forecast to drop, and that's going to slow the reaction.

 

[Gosut]

Update: There seem to be no more visible voids in the bottle, other than small bubbles on the steel wool. That said, the steel wool is way more intact than expected. Individual strands are visible. I would question whether the vinegar is reacting with the steel at all except that part that spilled out of the cap and onto the folded paper towel shows an irregular orange ring, with a similar spot on the remains of the label on the side of the bottle. My guess is the orange is rust where iron dissolved in the vinegar oxidized. But that it dissolved rather than formed ferrous acetate seems significant. We know that iron and acetic acid form ferrous acetate, and that iron liquor dye is made from iron and vinegar, but it seems to be taking far longer for the steel to combine with the acetic acid than anticipated.

For what it's worth, temperatures have been in the 50°'s F / 10°s C since overnight, and that has to have slowed the reaction.

[Wepster]

Again, this may or may be helpful........cleaning vinegar has about 9% acid, and you can buy concentrate  - I got some on Amazon    https://www.amazon.com/gp/product/B091FZRT1X/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

plain old white vinegar is mostly water, as you noted only 4 or 5% acid.

 

[Gosut]

Update:

Even with the cooler temperatures, there are now noticeable bubbles on the steel wool, with a bubble every now and then breaking free and floating to the top. So far, no orange in the bottle itself, so hopefully there's no oxygen getting involved in this. This is why I wanted to use the soft drink bottle, filling it up to the cap in order to reduce surface area exposed to air. Not quite ready to remove the cap and inspect the surface of the vinegar.

There's problems with the bottle this full. A length of tubing attached to the top to lengthen the neck and allow for bubbles bursting at the top might be better, but don't know if it's possible to get such locally or if any exists in that diameter. Would have to cobble a connection. It would be very easy to spend a lot of money on this.

I should have used a smaller bottle, since this is an experiment. Soft drink bottles seem to be stouter than plastic bottled water bottles, and would trust them more for this, even with the vent hole in the cap.