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Why is OH a stronger base than fluoride?
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Mark Young
Why is OH a stronger base than fluoride?
Hydrogen fluoride is a weak acid (unlike HCl, HBr, and HI) because of extensive hydrogen bonding in HF. For any acid/base conjugate pair, KaKb = Kw.
Ka for HF is 7.2E-4. Therefore, Kb for F^- is 1.4E-11.
The hydroxide ion is the conjugate base of water. It is, in fact, the classical base in the Arrhenius model of acid/base behavior.
Kw =1.0E-14 corresponding to the reaction: H2O → H^+ + OH^-
The reverse reaction, H^+ + OH^- → H2O essentially goes to completion. Thus, the hydroxide ion is a strong base.
(This is why replacing hydroxide ions with fluoride ions in tooth enamel is effective in preventing cavities. The hydroxide ions react with acid in food, weakening the enamel. The fluoride ion, as a much weaker base than the hydroxide ion, does not react with the acid in food.)
Hydrogen fluoride is a weak acid (unlike HCl, HBr, and HI) because of extensive hydrogen bonding in HF. For any acid/base conjugate pair, KaKb = Kw.
Ka for HF is 7.2E-4. Therefore, Kb for F^- is 1.4E-11.
The hydroxide ion is the conjugate base of water. It is, in fact, the classical base in the Arrhenius model of acid/base behavior.
Kw =1.0E-14 corresponding to the reaction: H2O → H^+ + OH^-
The reverse reaction, H^+ + OH^- → H2O essentially goes to completion. Thus, the hydroxide ion is a strong base.
(This is why replacing hydroxide ions with fluoride ions in tooth enamel is effective in preventing cavities. The hydroxide ions react with acid in food, weakening the enamel. The fluoride ion, as a much weaker base than the hydroxide ion, does not react with the acid in food.)
Hydrogen fluoride is a weak acid (unlike HCl, HBr, and HI) because of extensive hydrogen bonding in HF. For any acid/base conjugate pair, KaKb = Kw.
Ka for HF is 7.2E-4. Therefore, Kb for F^- is 1.4E-11.
The hydroxide ion is the conjugate base of water. It is, in fact, the classical base in the Arrhenius model of acid/base behavior.
Kw =1.0E-14 corresponding to the reaction: H2O → H^+ + OH^-
The reverse reaction, H^+ + OH^- → H2O essentially goes to completion. Thus, the hydroxide ion is a strong base.
(This is why replacing hydroxide ions with fluoride ions in tooth enamel is effective in preventing cavities. The hydroxide ions react with acid in food, weakening the enamel. The fluoride ion, as a much weaker base than the hydroxide ion, does not react with the acid in food.)
Hydrogen fluoride is a weak acid (unlike HCl, HBr, and HI) because of extensive hydrogen bonding in HF. For any acid/base conjugate pair, KaKb = Kw.
Ka for HF is 7.2E-4. Therefore, Kb for F^- is 1.4E-11.
The hydroxide ion is the conjugate base of water. It is, in fact, the classical base in the Arrhenius model of acid/base behavior.
Kw =1.0E-14 corresponding to the reaction: H2O → H^+ + OH^-
The reverse reaction, H^+ + OH^- → H2O essentially goes to completion. Thus, the hydroxide ion is a strong base.
(This is why replacing hydroxide ions with fluoride ions in tooth enamel is effective in preventing cavities. The hydroxide ions react with acid in food, weakening the enamel. The fluoride ion, as a much weaker base than the hydroxide ion, does not react with the acid in food.)
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