What is an Acid?

Ca(OH)2  Ca+2 + 2OH- (Base) The Arrhenius Theory Svante Arrhenius, a Swedish chemist, noted that acids have hydrogen while bases have hydroxide. Thus an acid was a H+ donor while a base was a OH- donor. This was the first theory of the difference between acids and bases but was later found to be too limited. HCl  H+ + Cl- (Acid) H2SO4  2H+ + SO4-2 (Acid) NaOH  Na+ + OH- (Base) Ca(OH)2  Ca+2 + 2OH- (Base)

A Hydrogen Ion A hydrogen ion is a hydrogen atom that has lost an electron. Thus a hydrogen ion (H+) is a single proton.

The Bronstead-Lowry Theory In the Bronstead-Lowry theory of acids and bases, an acid is a proton donor while a base is a proton acceptor.

Bronstead-Lowry Acid and Base Acids donate H+ while bases accept H+ .

The Hydronium Ion Water easily accepts a hydrogen ion and is then called a hydronium ion. A hydrogen ion and a hydronium ion are equivalent in that free hydrogen ions do not exist in water except as hydronium ions.

Amphiprotic Substances An amphiprotic substance can act as either an acid or as a base. It can give or accept protons. Water is amphiprotic.

Other Amphiprotic Substances Note that an amphiprotic species must have H in its formula because it has to be able to give a proton as well as receive a proton

Conjugate Acids and Bases The conjugate acid of a substance is a species with one more proton (H+). A conjugate base of a substance is a species with one less proton (H+).

Other Conjugate Acids and Bases Is the CH3COO- a conjugate base or acid of CH3COOH?

Other Conjugates Identify the acid and base and their conjugates for the forward reaction.

Conjugate Chart When one conjugate of a pair is weak, it means that the other conjugate of the pair is strong.

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