Question by  jojogeorge (53)

Why does lemon juice react with copper pennies?

Why does this happen, and what exactly is the reaction?


Answer by  LeheckaG (1826)

In air or water, the Copper pennies corrode or "rust", and form a Copper Oxide coating. Lemon juice is a (weak) Citric acid solution, so it has "surplus" (H+) Hydrogen ions to "donate" to other ions or molecules. Citric acid and Copper Oxide coating: C3 H5 O (COOH)3 + Cu O ---> Cu(COOH)2 + (C3 H5 O)2 O3

posted by Anonymous
the term rust is incorrect because that implies that it is iron oxide but it is in fact copper oxide  add a comment

Answer by  jason43 (47)

Because lemon juice is acidic and has a common ph range of 2-3 and reacts with metals and serves as a good cleaning fluid for metallic surfaces.


Answer by  leeyjin (6)

Citric acid in lemon juice etches away copper oxide that gives the penny the dark color. When the oxide is removed, the copper metal underneath is exposed.


Answer by  jheremans (1446)

Lemon juice is an acid, specifically citric acid, and like most acids it dissolves organic material quite quickly. Acids can also dissolve specific metals depending on the metal and acid being introduced. In the case of a copper penny, the citric acid is not in fact eating the copper shell, but the zinc core of the penny.


Answer by  codyligon (107)

When copper pennies become "dirty" they have formed a layer of copper oxide on their surface. Copper oxide is a weak base and consequentially reacts with a weak acid, such as lemon juice.


Answer by  Jenniferlm21 (5)

It is because when the acid (citric acid) of the lemon juice comes in contact with the zinc core of the penny (the outside of the penny)it creates a reaction.


Answer by  cmayfieldisawesome (40)

The citric acid dissolves the copper oxide that builds up on the surface of a penny due to oxidation from exposure to the atmosphere. So it does't really react with the penny itself, but with oxide on the surface.


Answer by  BobSXLemon (110)

The acid in the juice is dissolving the copper oxide surface layer - tarnish - and leaving pure copper behind. Acid and copper oxide gives water and a copper compound.

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