When I am writing a half-reaction with a corroding metal that is in deionized water, what can i assume there to be in the water that can show up in a half-reaction?
When writing a half-reaction involving a corroding metal in deionized water, it is important to consider the dissolved substances that could be present in the water. Deionized water is purified to remove most minerals, ionic compounds, and impurities. However, it is essential to keep in mind that deionized water can still contain traces of dissolved gases, such as oxygen (O2) and carbon dioxide (CO2), which can influence the corrosion process.
To determine if any particular substance will appear in the half-reaction, we need to consider the reactivity series of metals and their tendency to displace other metals from aqueous solutions. The reactivity series arranges metals in order of their reactivity, with the most reactive metals at the top and the least reactive at the bottom.
In general, highly reactive metals like potassium (K), sodium (Na), and calcium (Ca) will react with water to produce hydrogen gas (H2) and metal hydroxides. However, metals towards the middle of the reactivity series, like iron (Fe) or zinc (Zn), may undergo various half-reactions depending on the presence of dissolved substances.
For example, in the case of iron (Fe) corrosion in deionized water, the primary half-reaction involves the Fe metal losing electrons to form Fe2+ ions:
Fe(s) -> Fe2+(aq) + 2e-
However, if there is dissolved oxygen (O2) present in the water, it can further react with the Fe2+ ions to form iron(III) hydroxide (Fe(OH)3):
4Fe2+(aq) + 3O2(aq) + 6H2O(l) -> 4Fe(OH)3(s)
Therefore, the appearance of dissolved substances like oxygen (O2) can affect the half-reaction of corroding metals in deionized water. It is essential to consider the specific metal being corroded and the possible reactants or compounds present in the water to determine the appropriate half-reaction.