Chapter 13: Acids & Bases “The end is near”. 13.1 The Arrhenius and Bronsted- Lowry Theories of...

Chapter 13: Acids & Bases“The end is near”

13.1 The Arrhenius and Bronsted-Lowry Theories of Acids and Bases

• A. Properties of Acids and Bases

– 1. Acids• Ionize when put into water• React with active metals (Group I, II) to

produce Hydrogen gas• Neutralized with bases• Have a sour taste• Found in citrus fruits, vinegar, soda• pH 0-7


– 2. Bases• Ionize when put into water• Neutralized with acids• Have a bitter taste• Feel Slippery• Found in soaps, cleaners, antacids, etc.• pH 7-14


• B. Arrhenius Definitions of Acids and Bases– 1. Acids

• Produces H+ in soln; formula starts with H

– 2. Bases• Produces OH- in soln; formula ends with OH

– 3. Another definition needed• Too many substances that didn’t fit the

definition so it needed to be expanded

13.1 The Arrhenius and Bronsted-Lowry Theories of Acids and Bases • C. Bronsted-Lowry Model

– 1. Definitions • Acid = Proton (Hydrogen) Donor • Base = Proton (Hydrogen) Acceptor


– 2. Conjugate acid• The substance formed from the base

– 3. Conjugate base• The substance formed from the acid


– 4. Acid-Base Pairs• Acid and its conjugate base -or- • Base and its conjugate acid

– 5. Generalized equation:

H—X + B <----> X-1 + HB+1

Acid Base CB CA


• Example 15L.1 Write the Bronsted Lowry equations for the weak acid HNO2 and the weak base NH3, identifying the conjugate acid-base pairs in each equilibrium. (react with water)

13.1 The Arrhenius and Bronsted-Lowry Theories of Acids and Bases• Example 15L.2 Write the equilibrium

expressions for the interactions between NH3 and HCO3

1- and between H3PO4 and H2O, identifying the conjugate acid-base pairs in each equation.


– 8. Amphiprotic species• Substances that can ionize as either an

acid or a base depending on the properties of the other species in soln; can have properties of acid or base


– 9. Acid ionization constant• Keq expression for an acid dissociation

– 10. Base ionization constant • Keq expression for a base dissociation


– 11. Relative strengths of acids and bases

– Strong acids: Br I Cl SO NO ClO (4, 3, 4)

– Strong bases: Group I except 1st one and group II except 1st two

– All other acids and bases are considered weak

13.2 Self-Ionization of Water, The pH Scale

• A. Water dissociation constant– 1. In water solution

• H2O(l) + H2O(l) H3O+(aq) + OH-

(aq)

acid base CB CA

OR: H2O(l) H+1(aq) + OH-1

(aq)

– 2. For any sample of water molecules:

• 2 H2O (l) H3O+ (aq) + OH-

(aq)


– 3. Keq = [H+] [OH-]

– 4. Kw = 1.0x10-14

– 5. Neutral solution [H+]=[OH-]=1.0x10-7

– 6. Acid solution[H+] > 1x10-7

7. Basic Solution[H+] < 1x10-7


• Example 15.3 A sample of tap water has a [H+] = 2.8 x 10-6M. What is the [OH-]?

13.3 The pH scale pH and pOH

1. Definition• “The Potential of Hydrogen”

• pH = -log [H+]


– 2. Size of pH• Ranges from 0 to 14• 0~7 = ACID• 7~14 = BASE• 7 = Neutral

– 3. pOH definition• pOH = -log [OH-]

– 4. pH and pOH relationship• pH + pOH = 14


• Example 15.L4 Calculate the pH and pOH of a 0.25 M phosphoric acid solution whose [H+] is 0.040M.

• NOTE – the concentration of H+ is much lower than the molarity, weak acids don’t completely dissociate


• Example 15.L5 Calculate the pH and pOH of a 0.010 M formic acid solution whose [H+] is 1.8 x 10-

4M.• NOTE – the concentration of H+ is much lower than

the molarity, weak acids don’t completely dissociate

13.3 The pH Scale

– 7. pH of strong acids and strong bases

• a. Strong acids and bases dissociate completely in aqueous solution:

• HCl(aq)H+1(aq)+Cl-1(aq) over 99%

ions• Single headed arrow


• Example 15L.6 Calculate the [H+], pH, and [OH-] of a 0.15M solution of the strong acid, HNO3.

13.3 The pH Scale

c. Strong bases completely dissociate in aqueous solution:

NaOH(aq) Na+1(aq) + OH-1

(aq) over 99% ions

Single headed arrow

15.3 The pH Scale

• Example 15L.7 State the pH, pOH, [H+], and [OH-] of a solution made by dissolving 5.00 g of Ba(OH)2 - a strong base - in 1.00 L of water.

13.4-5 Equilibrium Solutions of Weak Acids and Weak Bases• A. Weak Acids and Dissociation

Constants– 1. Weak acids are partly

dissociated in water solution:

CH3COOH(aq)H+1(aq)+CH3COO-1

(aq) over 99% molecules

Double headed arrow/reversible reaction

13.4-5 Equilibrium Solutions of Weak Acids and Weak Bases

– 2. Ka = Acid dissociation constant • CH3COOH(aq) H+1

(aq) + CH3COO-1(aq)

– 3. Size of Ka values• Large Ka values = lots of protons given off =

relatively “strong” acid

• Small Ka values = few protons given off = very little dissociation

• If Ka is smaller than 10-4, “x” is negligible in an IRE

– For quadratic approximations only!


– 4. pKa

• pKa = -log Ka


• 5. Example 15L.8 Nicotinic acid is a monoprotic acid (only one ionizable H) and another name for the vitamin, niacin. Minute quantities of this substance are found in all living cells. When 0.10 mole of nicotinic acid, HC6H4NO2, is dissolved in enough water to make 1.00 L of solution, the pH is found to be 2.92. Calculate the Ka for this acid. What is the percent dissociation of this acid?

Continued• What is the percent

dissociation of this acid?

15.4 Equilibrium Solutions of Weak Acids and Weak Bases

• 6. Example 15L.9 Propionic acid, which occurs in dairy products, is a weak acid often abbreviated Hpro. If 0.10 mole of this acid is mixed with enough water to make 1.00 L of solution, calculate the pH of the solution. Ka = 1.3 x 10-5.

15.4 Equilibrium Solutions of Weak Acids and Weak Bases• B. Weak Bases and their

Dissociation Constants – 1. Two types of substances act like

weak bases in aqueous solution: • Nitrogen-containing compounds

– Ex. NH3

• Anions of acids– Ex. HCO3

-


• 2. Example 15L.10 Write the dissociation equilibria that show how each of the following acts like a weak base in aqueous solution: CN1-, PO4

3-, S2-.


– 3. Equilibrium constant for a weak base, Kb

• Base dissociation constant

• Ex. PO4-3

15.4 Equilibrium Solutions of Weak Acids and Weak Bases• 4. Example 15L.11 Calculate the [OH-], [H+] and

pH of a 0.75 M solution of carbonate ion which has a Kb of 2.1 x 10-4.


– 5. Relationship between Ka and Kb

• Ka x Kb = Kw = 1.0 x 10-14

• pKa x pKb = pKw = 14.0

15.4 Equilibrium Solutions of Weak Acids and Weak Bases• 6. Example 15L.12 Propionic acid, HPro, has a

Ka of 1.3 x 10-5. Calculate the Kb for the propionate ion, Pro-.

Polyprotic Acids

• 1. Definition and examples– Acid that gives off more than 1 H+ when

put into water• 1st Proton usually given off rapidly• Subsequent protons are given off with

increasing difficulty (stronger bases at each step)

• 2. Phosphoric acid• H3PO4 = 3 H’s means polyprotic, specifically

triprotic

13.6 Neutralization Reactions and Titration Curves for Strong Acids and Bases• 1. Definitions

– Complete dissociations• No need to worry about Ka or Kb

– Strong Acid + Strong Base --> H2O + Salt

– (JUST LIKE THE TITRATION LAB WE DID THIS WEEK)

• 2. Equation– (#H+) Ma Va = Mb Vb (#OH-)

15.10 Neutralization Reactions and Titration Curves for Strong Acids and Bases• 3. Curve

– Graph of pH versus volume of titrant from a buret

– Shows us where the equivalence point of the neutralization reaction is located

HOMEWORK:

Worksheets from other book:Chapter 19 pages 109-110 and

113

You can use the books on the counter next to ours, this is from that book.

Chapter 13: Acids & Bases “The end is near”. 13.1 The Arrhenius and Bronsted- Lowry Theories of...

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