Chem 18 Lecture 1 Exam 3 Acids and Bases (1)

8/6/2019 Chem 18 Lecture 1 Exam 3 Acids and Bases (1)

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Acids and Bases



Brønsted-Lowry Acids and Bases

� Concept of conjugate acid-base pair

� CN-(aq) + H2O(l) HCN(aq) + OH-(aq)

� CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+

(aq)



Acid-Base Properties of Water

� H2O + H2O H3O+ + OH-

� for the autoionization of water:� Kw = [H3O+][OH-]

� Ion-product constant

� At 25°C, Kw = 1.0 x 10-14

� from [H3O+]=[OH-]= 1.0 x 10-7 M



pH

� pH = -log[H3O+]

� Acidic: [H3O+] > 1.0 x 10-7, pH < 7.00

� Basic: [H3O+] < 1.0 x 10-7, pH > 7.00� Neutral: [H3O+] = 1.0 x 10-7, pH = 7.00

� pH + pOH = 14.00 (derive please)

� pH is measured by a pH meter



Calculate.

� How many moles of hydroxide ions is present

in a 500-mL HCl solution whose pH = 2.74?

�Calculate the pH of a NaOH solution if [OH-] =3.1 x 10-4 M



Strength of Acids and Bases

� Strong acids/bases are strong electrolytes that

are assumed to ionize completely in water

�

HNO3(aq) + H2O H3O+

(aq) + NO3

-

(aq)

� Weak acids/bases ionize only to a limited

extent in water� NH3(aq) + H2O NH4

+(aq) + OH-

(aq)



See animation



Conjugate acid-base pairs properties

� 1. If an acid is strong, its conjugate base has

no measurable strength

�

2. H3O+

is the strongest acid that can exist inaqueous solution

� 3. OH- is the strongest base that can exist in

aqueous solution



Calculate.

� What is the pH of a 0.020 M Ba(OH)2 solution?





Ka Acid Base

Name Formula Formula Name

Large Perchloric acid HClO4 ClO4- Perchlorate ion

3.2 * 109 Hydroiodic acid HI I- Iodide

1.0 * 109

Hydrobromic acid HBr Br- Bromide1.3 * 106 Hydrochloric acid HCl Cl- Chloride

1.0 * 103 Sulfuric acid H2SO4 HSO4- Hydrogen sulfate

ion

2.4 * 101 Nitric acid HNO 3 NO3- Nitrate ion

-------- Hydronium ion H3O+ H2O Water

5.4 * 10-2 Oxalic acid HO2C2O2H HO2C2O2- Hydrogen oxalate

ion1.3 * 10-2 Sulfurous acid H2SO3 HSO3

- Hydrogen sulfite

ion

1.0 * 10-2 Hydrogen sulfate ion HSO4- SO4

2- Sulfate ion

7.1 * 10-3 Phosphoric acid H3PO4 H2PO4- Dihydrogenphospha

te ion

7.2 * 10-4 Nitrous acid HNO 2 NO3- Nitrite ion

6.6 * 10-4 Hydrofluoric acid HF F - Fluoride ion

1.8 * 10-4 Methanoic acid HCO2H HCO2- Methanoate ion

6.3 * 10-5 Benzoic acid C6H5COOH C6H5COO- Benzoate ion

5.4 * 10-5 Hydrogen oxalate

ion

HO2C2O2- O2C2O2

2- Oxalate ion

1.8 * 10-5

Ethanoic acid CH3COOH CH3COO Ethanoate (acetate)ion



4.4 * 10-7 Carbonic acid CO32- HCO3

- Hydrogen carbonate ion

1.1 * 10-7 Hydrosulfuric acid H2S HS- Hydrogen sulfide ion

6.3 * 10-8 Dihydrogen phosphateion

H2PO4 - HPO4 2- Hydrogen phosphate ion

6.2 * 10-8 Hydrogen sulfite ion HS- S2- Sulfite ion

2.9 * 10-8 Hypochlorous acid HClO ClO- Hypochlorite ion

6.2 * 10-10 Hydrocyanic acid HCN CN- Cyanide ion

5.8 * 10-10

Ammonium ion NH4

+

NH3 Ammonia5.8 * 10-10 Boric acid H3BO3 H2BO3

- Dihydrogencarbonate

ion

4.7 * 10-11 Hydrogen carbonate ion HCO3- CO3

2- Carbonate ion

4.2 * 10-13 Hydrogen phosphate ion HPO42- PO4

3- Phosphate ion

1.8 * 10-13 Dihydrogen borate ion H2BO3- HBO3

2- Hydrogen borate ion

1.3 * 10-13 Hydrogen sulfide ion HS- S 2- Sulfide ion

1.6 * 10-14 Hydrogen borate ion HBO32- BO3

3- Borate ion

--------- water H2O Hydroxide



Analyze.

� Predict the direction of the reaction:

� HNO2(aq) + CN-(aq) HCN(aq) + NO2

-(aq)

Will the equilibrium constant be greater than or

less than 1 in the reaction below?

CH3COOH(aq) + HCOO-(aq) CH3COO-

(aq) + HCOOH(aq)



Ionization constants

� Ka acid

�HF(aq) H+(aq) + F-(aq)

� Ka = = 7.1 x 10-4



Calculate.

� What is the pH of a 0.50 M HF solution?

�What is the acid ionization constant of a 0.10M HCOOH solution whose pH is 2.39?



Percent ionization

� Measure of the extent of ionization

�=





Base ionization constant

� NH3(aq) + H2O NH4+

(aq) + OH-(aq)

�Kb = = 1.8 x 10

-5



Calculate.

� What is the pH of a 0.40 M NH3 solution?





Ka,Kb,Kw

(1) CH3COOH(aq) + H2O(l) CH3COO-(aq) + H3O+

(aq) Ka

(2) CH3COO-(aq) + H2O(l) CH3COOH(aq) + OH-

(aq) Kb

(3) H2O + H2O H3O+

(aq) + OH-(aq) Kw

KaKb = Kw Ka= Kb =



Calculate.

� What is the base ionization constant of

acetate?

�

CH3COO-

(aq) + H2O(l) CH3COOH(aq) + OH-

(aq)



Molecular Structure and the Strength

of Acids

� 1. strength of the bond

� 2. polarity of the bond



Hydrohalic Acids

� HF (568.2 KJ/mol)

� HCl (431.9 KJ/mol)

� HBr (366.1 KJ/mol)

� HI (298.3 KJ/mol)

� F is the most electronegative element

� BUT HF<<HCl<HBr<HI

� -due to weaker bond





Oxoacids

� 2. Same central atom but different number of

attached O.

�

- acidity increases with increasing oxidationnumber of central atom

�

HClO4 > HClO3 > HClO2 > HClO



Base strength

� T he weaker the conjugate acid, the stronger

the base.

Acidity: H2SO3 > CH3COOH > HCN

Basicity: HSO3-

< CH3COO-

< CN-



Base strength

� Base strength increases with increasing

anionic charge

� N3- > O2- > F-



Lewis Concept

� A base is a substance that can donate a pair of

electrons while an acid is a asubstance



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Chem 18 Lecture 1 Exam 3 Acids and Bases (1)

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