The Chemistry of Acids and Bases

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Mg(OH)2 magnesium hydroxide “MOM” Milk of magnesia

Al(OH)3 aluminum hydroxide Maalox (antacid)

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Acid/Base definitions

Definition #1: Arrhenius (traditional)

Acids – produce H+ ions (or hydronium ions H3O+)

Bases – produce OH- ions

(problem: some bases don’t have hydroxide ions!)

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Arrhenius acid is a substance that produces H+ (H3O+) in water

Arrhenius base is a substance that produces OH- in water

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Acid/Base Definitions

Definition #2: Brønsted – Lowry

Acids – proton donor

Bases – proton acceptor

A “proton” is really just a hydrogen atom that has lost it’s electron!

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A Brønsted-Lowry acid is a proton donor

A Brønsted-Lowry base is a proton acceptor

acid

conjugate base

base

conjugate acid

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ACID-BASE THEORIES

The Brønsted definition means NH3 is a BASE in water — and water is itself an ACID

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Conjugate Pairs

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Learning Check!

Label the acid, base, conjugate acid, and conjugate base in each reaction:

HONORS ONLY!

HCl + OH-  Cl- + H2O

H2O + H2SO4  HSO4- + H3O+

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Acids & Base Definitions

Lewis acid - a substance that accepts an electron pair

Lewis base - a substance that donates an electron pair

Definition #3 – Lewis

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Lewis Acids & Bases

Formation of hydronium ion is also an excellent example.

Electron pair of the new O-H bond originates on the Lewis base.

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Lewis Acid/Base Reaction

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Lewis Acid-Base Interactions in Biology

The heme group in hemoglobin can interact with O2 and CO.

The Fe ion in hemoglobin is a Lewis acid

O2 and CO can act as Lewis bases

Heme group

Slide 23

The pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H+ (or OH-) ion. Under 7 = acid 7 = neutral Over 7 = base