This is my first post here, sorry if I'm in the wrong forum.
For an upcoming school project, I plan to investigate the effects of sodium chloride on the rate of reaction between acetic acid and rust. My school has this "personal engagement" requirement, so my justification was that the idea was inspired by cleaning the rust off of a steel bike chain using vinegar and salt with my dad when I was younger.
The problem is that in order for the project to get accepted, I need to provide an explanation behind why sodium chloride has this effect. I understand why vinegar removes rust - the acetic acid reacts with the iron(III) oxide, which produces the soluble salt iron(III) acetate - but I have no idea as to why sodium chloride works the way it does. From what I've gathered by searching online, there seems to be four possible explanations:
1. Sodium chloride is simply acting as an abrasive. This would be pretty bad if it were the case as it means that there is no chemical reaction taking place, meaning that I'd have to find a new project.
2. Sodium chloride increases the conductivity of the solution due to being an electrolyte. Because it disassociates, it allows for a faster transfer of electrons which means a faster rate of reaction.
3. The chloride forms a complex with the iron, which has an additive effect with the acetate.
4. A tiny portion of the sodium chloride reacts with the acetic acid, forming small amounts of hydrochloric acid which causes the rust to be removed faster.
These all seem pretty plausible to me, and I really can't tell which one is the correct answer. Can someone please explain which one is the case, and why the others aren't? Is it a combination of several factors? Or is the proper explanation not listed here?