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Unit 4: Equilibrium, Acids

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Unit 4: Equilibrium, Acids & Bases Part 2: Acids and Bases Bronsted Lowry Acids and Bases Autoionization of Water pH Strong Acids and Bases Weak Acids and Bases – PowerPoint PPT presentation

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Title: Unit 4: Equilibrium, Acids


1
Unit 4 Equilibrium, Acids BasesPart 2
Acids and Bases
  • Bronsted Lowry Acids and Bases
  • Autoionization of Water
  • pH
  • Strong Acids and Bases
  • Weak Acids and Bases
  • Ionization Constants
  • Buffers
  • Titrations
  • Lewis Acids and Bases

2
Review
  • Arrhenius Acid Substance that increases the
    concentration of H ions when dissolved in water
  • HCl (g) H (aq) Cl- (aq)
  • Arrhenius Base Substance that increases the
    concentration of OH- ions when dissolved in
    water.
  • NaOH (s) Na (aq) OH- (aq)

H2O
H2O
3
Review
  • The Arrhenius definition of acids and bases is
    limited to aqueous solutions
  • Two other common definitions for acids and bases.
  • Bronsted-Lowry acids and bases
  • Lewis acids and bases

4
Bronsted-Lowry Acids Bases
  • Bronsted-Lowry Acid
  • any substance that can transfer a proton (H ion)
    to another substance
  • a proton donor
  • HCl (g) H2O (l) H3O (aq) Cl- (aq)
  • A Bronsted-Lowry acid must have a hydrogen that
    can be lost as H

B-L acid
5
Bronsted-Lowry Acids Bases
  • Bronsted-Lowry Base
  • any substance that can accept a proton (H ion)
    from another substance
  • A proton acceptor
  • HCl (g) H2O (l) H3O (aq) Cl- (aq)
  • A B-L base must have an atom with a lone pair of
    electrons that can form a new bond to a hydrogen
    ion.

B-L acid
B-L base
6
Bronsted-Lowry Acids Bases
  • The H ion interacts strongly with the nonbonding
    pairs of electrons on water molecules, forming
    the hydronium ion
  • The hydronium ion is responsible for the
    characteristic properties of aqueous solutions of
    acids.

7
Bronsted-Lowry Acids Bases
  • H3O is a more realistic depiction of the
    hydrogen ion in solution but for convenience we
    often use H (aq) to depict the hydrated hydrogen
    ion.

HCl (g) H20 (l) ? H3O (aq) Cl- (aq) HCl
(aq) ? H (aq) Cl- (aq)
8
Bronsted-Lowry Acids Bases
  • Some substances like water are amphoteric
  • Capable of acting as either an acid or a base
  • H2O (l) HCl (g) ? H3O (aq) Cl- (aq)
  • NH3 (g) H2O (l) ? NH4 (aq) OH- (aq)

base
acid
9
Bronsted-Lowry Acids Bases
  • Examples of other amphoteric substances include
  • NaHCO3
  • NaH2PO4
  • NaHSO4
  • Alcohols such as ethanol

10
Bronsted-Lowry Acids Bases
  • In any acid-base equilibrium, both forward and
    reverse reactions involve proton transfers.
  • HNO2 (aq) H2O (l) NO2 (aq) H3O
    (aq)
  • Forward Reaction
  • B-L acid
  • B-L base
  • Reverse Reaction
  • acid
  • base

11
Bronsted-Lowry Acids Bases
  • The reaction between a BL acid and base produces
    a new acid (the conjugate acid) and a new base
    (the conjugate base).
  • HNO2 (aq) H2O (l) NO2 (aq) H3O
    (aq)
  • HNO2 and NO2- are called a conjugate acid-base
    pair.
  • H2O and H3O are also a conjugate acid-base pair.

BL acid
conjugate base
BL base
conjugate acid
12
Bronsted-Lowry Acids Bases
  • Conjugate acid
  • The acid formed when a base gains a proton
  • Conjugate acid of H2O
  • H3O
  • Conjugate acid of SO4 2-
  • HSO4 -
  • NOTE The conjugate acid is always shown on the
    product side.

13
Bronsted-Lowry Acids Bases
  • Conjugate base
  • The base formed by removing a proton from an acid
  • Conjugate base of H2O
  • OH -
  • Conjugate base of H2SO4
  • HSO4 -
  • NOTE The conjugate base is always shown on the
    product side.

14
Bronsted-Lowry Acids Bases
  • Conjugate acid-base pair
  • An acid and a base that differ only in the
    presence or absence of a single proton
  • HNO2 and NO2-
  • H3O and H2O
  • HCO3 - and CO32-
  • NH4 and NH3

15
Bronsted-Lowry Acids Bases
  • Example Identify the acid, base, conjugate acid
    and conjugate base for the following reaction.

HSO4 (aq) CO32- (aq) SO42- (aq) HCO3-
(aq)
16
Bronsted-Lowry Acids Bases
  • Example Identify the BL acid, BL base,
    conjugate acid and conjugate base in the
    following reactions.

17
Bronsted-Lowry Acids Bases
  • In any acid-base equilibrium, both forward and
    reverse reactions involve proton transfers.
  • HNO2 (aq) H2O (l) NO2 (aq) H3O
    (aq)

Conjugate acid
Conjugate base
base
acid
  • How can we predict the position of the chemical
    equilibrium?

18
Bronsted Lowry Acids Bases
  • The relative strengths of the acid and the
    conjugate acid can be used to predict the
    position of the equilibrium.
  • Equilibrium favors the formation of the weaker
    acid.
  • The stronger acid more effectively loses a proton
    than its conjugate acid

19
Bronsted Lowry Acids Bases
  • Every substance can be categorized as either
  • strong acid
  • ionizes completely
  • weak acid
  • ionizes partially
  • solutions contain mixture of acid molecules,
    hydronium ion, and conjugate base
  • negligible acidity
  • no tendency to form H in solution

20
Bronsted-Lowry Acids Bases
  • The seven most common strong acids
  • HCl hydrochloric acid
  • HBr hydrobromic acid
  • HI hydroiodic acid
  • HNO3 nitric acid
  • HClO3 chloric acid
  • HClO4 perchloric acid
  • H2SO4 sulfuric acid

You must know these acids by name and formula.
21
Bronsted-Lowry Acids Bases
  • Examples of common weak acids
  • acetic acid,
  • citric acid,
  • phosphoric acid
  • Examples of substances with negligible acidity
  • CH4
  • H2
  • OH
  • NH3

22
Bronsted-Lowry Acids Bases
  • An inverse relationship exists between the
    strength of an acid and its conjugate base or
    between a base and its conjugate acid.
  • Strong acids form very weak conjugate bases
    (usually have negligible basicity).
  • Weak acids form stronger (but still fairly weak)
    conjugate bases
  • Substances with negligible acidity form very
    strong bases.

23
Bronsted-Lowry Acids and Bases
  • The stronger the acid, the weaker the conjugate
    base
  • The stronger the base, the weaker the conjugate
    acid

24
Bronsted-Lowry Acids Bases
  • Example Does the following acid/base
    equilibrium favor the reactants or products?
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