For my school project I was going to measure the rate that salt has on the rusting of iron.

To do this I set up an experiment where I had 15 beakers containing 200 milliliters of distilled water. I poured into the beakers varying moles of salt $\ce{(NaCl)}$. I had $\pu{0mol}$, $\pu{0.25mol}$, $\pu{0.5mol}$, $\pu{0.75mol}$ and $\pu{1mol}$ of salt. So now there are three beakers for every concentration. I then put a iron nail in every beaker, put plastic wrap over them to stop some of the oxygen flow and left it be for 10 days.

What I was surprised to find was that the beakers with no salt in them had more rust than the one ones that had. It was exactly the opposite of what I expected would happen, and I can't find a website that explains how this occurs. Does anyone have an explanation?

  • 1
    $\begingroup$ um, that's not normal. Are you sure you didn't mix up the ordering of your beakers? Concentration of oxygen in the water is also quite important for rusting, so are you sure all conditions are exactly the same in all beakers? Also, what are your nails out of, do they have a coating? $\endgroup$ – Fl.pf. Jun 13 '17 at 11:03
  • $\begingroup$ The nails did not have any coating. However, I did find something that did explain what was going on in my experiment. chemistry.stackexchange.com/questions/22043/… $\endgroup$ – Dude that needs help Jun 13 '17 at 11:46
  • $\begingroup$ My nails where completely submerged and the plastic wrap blocked off some of the oxygen, so I would imagine that this would be the explanation. $\endgroup$ – Dude that needs help Jun 13 '17 at 11:47
  • $\begingroup$ Triplicate results are recommended, so you should repeat the experiment two more times. $\endgroup$ – J. Ari Jun 13 '17 at 13:39
  • $\begingroup$ I wouldn't just throw the results away, they can be used to learn and understand the process maybe even better than the right results! $\endgroup$ – Fl.pf. Jun 13 '17 at 14:12

Corrosion is a balancing game. In this case, by covering the beakers, you have limited the driving force for oxygen dissolution by limiting the amount of oxygen available to dissolve into solution and then the higher salt concentrated solution is able to further minimize the amount of oxygen that can be dissolved and participate in the redox reaction (as explained in the linked question's answer).


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