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Hi! I had a question about water and it's Kw value of 1x10^-14. Is water considered a strong acid/base? Since it is amphiprotic it can be an acid or a base, but since it has a Kw value, does that make it a weak acid/base? I remember Dr. Lavelle mentioning that only weak acids or bases have Ka values and I was wondering if this applies to water as well. Thanks!
Yes you are correct water can act as an acid and base because its amphiprotic. Pure water is both a weak acid and base. By itself water only forms a small number of H3O+ and OH- ions so it is considered a weak acid and base.
To add on, pure water is neither acidic nor basic. The acid (H3O+) and base (OH-) exist mostly in similar concentrations, so we say water is neutral. However, water can both act as an acid and a base when molecules are in water because of its amphiprotic properties.
Water can act as a weak acid or a weak base, but in terms of pH, it is neutral. The little amounts of H30+ and OH- it does contain is exclusively in equal amounts, so they cancel out. In terms of Ka values, a large Ka value indicates a strong acid, not just any Ka value. Hope this helps!
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