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Acid
A substance that has the potential to donate a proton or accept an electron pair.
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Acidic
Having a pH less than 7 or a pOH greater than 7.
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Amphiprotic
A species that can either donate or accept a proton, e. g. water.
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Amphoteric
A species that can either donate or accept a hydroxide ion, such as Al(OH)3. Many chemistry texts incorrectly use this term to mean that a substance can act as either an acid or a base.
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Arrhenius Model
Arrhenius proposed that acids are substances that produce protons (H+) in aqueous solution, whereas bases produce hydroxide ions (OH-) in aqueous solution. Compare his model with the Bronsted-Lowry definition and the Lewis definition.
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Base
A substance that can accept a proton, release OH-, or donate an electron pair.
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Basic
Having a pH greater than 7 or a pOH less than 7.
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Bronsted-Lowry Definition
Bronsted and Lowry define an acid as a proton (H+) donor and a base as a proton acceptor. Compare this model with the Arrhenius Model and the Lewis definition.
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Conjugate Acid
A molecule that can be described as a base that has gained one proton.
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Conjugate Base
A molecule that can be described as an acid that has lost one proton.
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Dissociate
Separate into its ion constituents.
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Lewis Definition
Lewis defined an acid as an electron pair acceptor and a base as an electron pair donor. Compare his model with the Arrhenius model and the Bronsted-Lowry definition.
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Oxyacid
A molecule of the form AOn(OH)m, where A is a non-metal.
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Pauling-Ricci rule
For oxyacids, the more electron withdrawing (more electropositive) the non- metal center, the stronger the acid due to a weakening of the O-H bond. This trend is approximated by the equation: PKa= 8 - 9f + 4n, where f is the formal charge on A when all oxygens are singly bound to A, and n represents the number of O atoms bound to A that are not bound to an H.
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pH
A measure of the hydrogen ion concentration, it is equal to - log [H+], where [H+] is the concentration of protons.
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pKa
A measure of the strength of an acid, it is equal to – log Ka, where Ka is the acid dissociation constant in water.
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pKb
A measure of the strength of a base, it is equal to – log Kb, where Kb is the base dissociation constant in water.
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pOH
A measure of the hydroxide ion concentration, it is equal to - log [OH-], where [OH-] is the concentration of hydroxide ions.
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Strong Acid
An acid with a pKa less than zero. Strong acids completely dissociate in water.
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Strong Base
A base with a pKb less than zero. Strong bases completely dissociate in water.
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Weak Acid
An acid with a pKa greater than zero. Weak acids do not completely dissociate in water.
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Weak Base
A base with a pKb greater than zero. Weak bases do not completely dissociate in water.
