# Different reactions of clean and rusty iron nails in vinegar (acetic acid)

I have submerged a iron nail in vinegar twice recently. What is puzzling me is the different results each time. The first time I submerged it, it was covered in rust. When I put it in the solution of vinegar, I got a red precipitate dissolved in the solution that I believe was Iron(II) and Iron(III) acetate. However, when I put the newly cleaned nail in ANOTHER bath of the same concentration of vinegar, I did get some bubbles but no red precipitate that was dissolved in the solution. It's only been about 2 days, though. However, there was a black precipitate on the surface of the nail, but I do not believe it is iron acetate because of its color.

I am confused as to the results because Iron is higher than hydrogen on the activity series, so it SHOULD be reacting with the vinegar to give me that red precipitate and hydrogen gas. I added some hydrogen peroxide to the solution to oxidize the iron, and the solution is getting a reddish tint to it.

Why do you think I am not getting that reddish precipitate when I put in the cleaned iron nail in the new vinegar solution? Thank you!

In your first experiment, the rust ($\ce{Fe2O3. xH2O}$) probably reacted with vinegar to form Iron (III) acetate which makes the solution reddish in color.

In your second experiment, the iron on the clean nail surface would have reacted with vinegar to form Iron (II) acetate. There are two main reasons why the solution might appear to have no change:

1. Usually, Iron (II) acetate is prepared using concentrated acetic acid and scrap iron (or ferrous oxide/hydroxide). Since vinegar is extremely dilute (around 5-8% acetic acid solution in water), the reaction would be very slow and the conc. of Iron (II) acetate formed will be very low.

2. Iron (II) acetate happens to be very soluble in water and has a very faint light green color in solution which is not easily detectable in lower concentrations.

Then again, when you added $\ce{H2O2}$ to the second solution, you mentioned that a reddish color appeared. This shows that the dissolved $\ce{Fe^2+}$ ions are oxidized to $\ce{Fe^3+}$. The $\ce{Fe^3+}$ formed will react with the acetate ions to form red Iron (III) acetate.

• What are the gas bubbles? – richard1941 Jul 26 '18 at 3:27

When you dip a rusty Iron Nail in veniger solution, the Viniger reacts with $\ce{Fe2O3.nH2O}$ (Rusty Iron or oxidized Iron). Whereas in case of clean nail, Its directly reacts with iron.

Your product is probably different due to this reason only, if I understood your question right. ;)

Edit : Chemical Equation for pure iron in venigar - $\ce{Fe(s) + 2CH3COOH(aq) -> Fe(CH3COO)2(aq) + H2(g)}$ Chemical Equation for Rusty iron in Venigar - $\ce{Fe2O3 + 8CH3COOH(aq) -> 4Fe(CH3COO)2(aq) + O2 + 4H2O}$ (Not sure about this equation.)

• So then what do you think the products of the reaction are? My thinking is that they are the same, but the clean nail just takes longer. However, I am not sure and that's why I asked. – user2514631 Jul 8 '13 at 23:44
• @ashu Your 2 reaction is wrong so it was good that you weren't sure ;) – Mithoron Aug 20 '15 at 0:04
• So, at first the bubbles from my rusted jackplane are oxygen, and after all the Fe3O4 is consumed, the iron is reducing the hydrogen ions in the solution? – richard1941 Jul 26 '18 at 3:29

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