Acids and Bases. Arrhenius Acids and Bases

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ACIDS AND BASES

CHAPTER 15

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Arrhenius Acids and Bases

(What we have been using to this point)

Arrhenius Acid is a substance that, when dissolved in water, increases the concentration of hydrogen ion, H+ or (hydronium ion H3O+).

Arrhenius Base is a substance that, when dissolved in water, increases the concentration of hydroxide ions, OH-.

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Bronsted-Lowry Acids & Bases

A. Definitions

1. Bronsted Acid: H+ (proton) donor

Ionizable hydrogen in the acid structure is usually bonded to an electronegative atom.

2. Bronsted Base: H+ (proton) acceptor

Base structure must have an unshared pair of electrons.

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B. Broader Definition For Acid-Base Reactions

Consider: HCl + NH4OH  NH4Cl + H2O

Consider: HF + HCO3-  H2CO3 + F-

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C. Amphiprotic Compounds

Some compounds can act as a Bronsted acid in one case and a Bronsted base in another case. It depends on the molecules the amphiprotic compound is reacting with.

Example: Water

HCl + H2O  H3O+ + Cl-

NH3 + H2O  NH4+ + OH-

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D. Conjugate Acid-Base Pairs

A conjugate acid-base pair consists of two species in an acid-base reaction, one acid and one base, that differ by the loss or gain of a proton.

Conjugate acid- species formed when a base has accepted a proton.

Conjugate base- species formed when an acid has donated or removed a proton.

Example: Acetic Acid

CH3COOH ⇌ CH3COO- + H+

CH3COOH + H2O ⇌ CH3COO- + H3O+

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Example Problems

1. What is the conjugate base of HNO3 ?

2. What is the conjugate acid of NH2- ?

3. Label all species in the following reaction.

H2PO4- + HCO3- ⇌ H2CO3 + HPO42-

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E. Strong vs. Weak Acids and Bases

1. Strong Acids and Bases

Essentially go to 100% ionization

Rxn normally shown with single headed arrow.

Strong Acids Strong Bases

HCl LiOH

HBr NaOH

HI KOH