| MadSci Network: Chemistry |
Hi Cindy,
That’s an interesting result from your experiment. Have you tried repeating it to see if the same thing happens?
I’m going to trust you, and ask that if you haven’t finished your lab write-up yet, make sure that your lab conclusions are your own. The steel wool undergoes a reaction in the vinegar (acetic acid) where the iron forms iron acetate (Fe(CH3COO)2) and hydrogen gas (H2). However, in order for the iron to oxidize, it needs air. When iron is exposed to oxygen, it forms FeO and Fe2O3. Rust. One of the hints was that the deposits were black and brownish-red. I think when you pulled the steel wool out of the jar of vinegar, you moved the vinegar around which put air bubbles into the vinegar, and provided oxygen for the oxidation reaction to occur. The air reacted (precipitated) with the iron that had been dissolved in solution. Before you disturbed the solution, there was no air to form iron oxide, so the iron remained dissolved.
To verify this, try it again with two pieces of steel wool and two jars of vinegar. Drop one steel wool in the vinegar and let it sit undisturbed for two days. Drop the other piece in the vinegar, and store it for two days, but shake it up as often as you can. I predict the shaken one will turn color and form the black and red deposits that you saw.
I’m glad you made a note of something you observed that seemed strange to you. That’s exactly how a lot of discoveries got noticed. Keep asking questions!
Jeff Yap
Mad Scientist
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