catalyzed by salts in the water. The tapes were restored to a readable form by a painstaking removal of the cement layer using the double replacement reaction:
NaHCO 3 (s) + KHC 4 H 4 O 6 (s) ---> NaKC 4 H 4 O 6 (s) + H 2 O(l) + CO 2 (g)
The product, rust, is a hydrated form of iron(III) oxide. The actual sequence of reactions that yields this overall change is quite complex, and not yet completely understood. An interesting characteristic is that the process is catalyzed by salt. One possible explanation of most of the data is as follows. The metallic iron in contact with water is oxidized
The acid needed for this comes from CO 2 dissolved in the water, forming an acidic solution. Concurrently, dissolved O 2 combines with the Fe 2+ ions as
1 / 2 O 2 + 2Fe 2+ + 5H 2 O ---> Fe 2 O 3 . 3H 2 O + 4H +
CO 2 (g) + 2NaOH(s) ---> Na 2 CO 3 (aq) + H 2 O(l)
Li 2 O(s) + H 2 O ---> 2LiOH(aq)
You might try carrying through the stoichiometric calculations.
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