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Animation: Dissociation of Water Molecules

by Pearson
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Dissociation of Water Molecules Occasionally, a hydrogen atom involved in a hydrogen bond between two water molecules shifts from one molecule to another. The hydrogen atom leaves its electron behind, so what actually shifts is a hydrogen ion, a single proton with a positive charge. The water molecule that lost the hydrogen ion is now a hydroxide ion, OH-, which has an extra electron and a negative charge. The hydrogen ion binds to the attracting water molecule, forming a hydronium ion, H3O+. The top equation summarizes the dissociation of water to form hydronium and hydroxide ions: H2O plus H2O gives H3O+ and OH-. Although this equation is technically correct, it is most useful to think of this process as the dissociation of a single water molecule into a hydrogen ion and a hydroxide ion, as shown in the bottom equation: H2O yields H+ plus OH-. The double arrows-- and the animation-- show that the dissociation of water is a reversible process. Hydrogen ions and hydroxide ions don't last very long on their own. In fact, a very small portion of the molecules in a glass of water are dissociated at any one time-- only about one water molecule in half a billion.
Dissociation of Water Molecules Occasionally, a hydrogen atom involved in a hydrogen bond between two water molecules shifts from one molecule to another. The hydrogen atom leaves its electron behind, so what actually shifts is a hydrogen ion, a single proton with a positive charge. The water molecule that lost the hydrogen ion is now a hydroxide ion, OH-, which has an extra electron and a negative charge. The hydrogen ion binds to the attracting water molecule, forming a hydronium ion, H3O+. The top equation summarizes the dissociation of water to form hydronium and hydroxide ions: H2O plus H2O gives H3O+ and OH-. Although this equation is technically correct, it is most useful to think of this process as the dissociation of a single water molecule into a hydrogen ion and a hydroxide ion, as shown in the bottom equation: H2O yields H+ plus OH-. The double arrows-- and the animation-- show that the dissociation of water is a reversible process. Hydrogen ions and hydroxide ions don't last very long on their own. In fact, a very small portion of the molecules in a glass of water are dissociated at any one time-- only about one water molecule in half a billion.