Lemon juice vs Lemon juice + salt

[pumaking94]

Hello,

I did an experiment to try and clean copper pennies with acids like lemon juice and vinegar. When they are dipped in only lemon juice, nothing happens. However, when you add salt, the effect is almost instantaneous. Why does adding salt to lemon juice (citric acid?) make it a much stronger acid? I've looked online and some people say it is because you have H+ and Cl- which makes hydrochloric acid but it also says that it is not the real explanation. If someone can explain what is really going on, that would be great.

 

[Borek]

I don't know what is the mechanism behind, but it is not change in the strength of the acid. For some reason chlorides speed up dissolution of whatever is present on the copper surface. Could be some complexation is involved, or perhaps when chlorides adsorb on the surface they weaken copper-oxide bond (I am just guessing, but similar mechanisms do exist).

 

[pumaking94]

I don't know what is the mechanism behind, but it is not change in the strength of the acid. For some reason chlorides speed up dissolution of whatever is present on the copper surface. Could be some complexation is involved, or perhaps when chlorides adsorb on the surface they weaken copper-oxide bond (I am just guessing, but similar mechanisms do exist).

So would it be correct to say that the chloride ions act as a catalyst? And would this work with any other negative ions such as F, Br? Sorry if these are simple questions I'm only in high school chemistry.

 

[Borek]

Catalyst - could be. Although it is also possible that one of the products is some chloride containing complex, in which case chlorides are being consumed, so they can't be classified as a catalyst. As to other halogen anions - hard to tell without testing. These are not simple questions

--
methods

 

[pumaking94]

Oh I see, I find chemistry so interesting and I was just curious. Thanks for your help!