1. Dr. Terace Fletcher tfletcher@ptcc.edu
CHM1033 Acid-Base
Dr. Terace Fletcher

2. General, Organic, and Biological Chemistry
Acids
Arrhenius acids
produce H+ ions in water
HCl(g) H+(aq) + Cl(aq)
are electrolytes
have a sour taste
turn litmus red
neutralize bases
General, Organic, and Biological Chemistry

3. Names of Acids
Acids with H + nonmetal prefix hydro- and end with -ic acid.
HCl hydrochloric acid
Acids with H + polyatomic ion  the end of the name of the polyatomic ion from -ate to -ic acid or -ite to -ous acid.
ClO3− chlorate HClO3 chloric acid
ClO2− chlorite HClO2 chlorous acid
ClO− hypchlorite HClO Hypochlorous acid
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

4. General, Organic, and Biological Chemistry
Bases
Arrhenius bases
produce OH− ions in water
taste bitter or chalky
are electrolytes
feel soapy and slippery
neutralize acids
General, Organic, and Biological Chemistry

5. Some Common Bases
Bases with OH ions are named as the hydroxide of the metal in the formula.
NaOH sodium hydroxide
KOH potassium hydroxide
Ba(OH)2 barium hydroxide
Al(OH)3 aluminum hydroxide
Fe(OH)3 iron (III) hydroxide
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

6. Comparing Acids and Bases
General, Organic, and Biological Chemistry

7. Brønsted–Lowry Acids and Bases
According to the Brønsted–Lowry theory,
acids donate a proton (H+)
bases accept a proton (H+)
General, Organic, and Biological Chemistry

8. NH3, A Brønsted–Lowry Base
In the reaction of ammonia and water,
NH3 is the base that accepts H+
H2O is the acid that donates H+
General, Organic, and Biological Chemistry

9. Conjugate Acid–Base Pairs
In any acid-base reaction, there are two conjugate
acid–base pairs:
each related by the loss and gain of H+
one occurs in the forward direction
one occurs in the reverse direction
conjugate acid–base pair 1
HA + B A− + BH+
conjugate acid–base pair 2
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

10. Conjugate Acid–Base Pairs
In the reaction of HF and H2O,
one conjugate acid–base pair is HF/F−
the other conjugate acid–base pair is H2O/H3O+
each pair is related by a loss and gain of H+
General, Organic, and Biological Chemistry

11. Conjugate Acid–Base Pairs (continued)
In the reaction of NH3 and H2O,
one conjugate acid–base pair is NH3/NH4+
the other conjugate acid–base is H2O/OH–
each pair is related by a loss and gain of H+
General, Organic, and Biological Chemistry

12. Strengths of Acids
Strong acids (such as hydrochloric acid) completely ionize (100%) in aqueous solutions.
HCl(g) + H2O(l) H3O+(aq) + Cl−(aq)
Weak acids (such as carbonic acid or acetic acid) dissociate only slightly in water to form a solution of mostly molecules and a few ions.
H2CO3(aq) + H2O(l) H3O+(aq) + HCO3−(aq)
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

13. Ionization of Water In the ionization of water,
H+ is transferred from one H2O molecule to another
one water molecule acts as an acid, while another acts as a base
H2O + H2O H3O+ + OH−
H:O: + H:O: H:O:H+ + :O:H−
H H H
water water hydronium hydroxide
ion(+) ion(-)
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

14. Pure Water is Neutral In pure water,
the ionization of water molecules produces small but equal quantities of H3O+ and OH− ions
molar concentrations are indicated in brackets as [H3O+] and [OH−]
[H3O+] = 1.0 x 10−7 M
[OH−] = 1.0 x 10−7 M
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

15. pH Scale The pH of a solution
is used to indicate the acidity of a solution
has values that usually range from 0 to 14
is acidic when the values are less than 7
is neutral with a pH of 7
is basic when the values are greater than 7
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

16. pH of Everyday Substances16 16

17. Calculating pH and pOH
Mathematically, pH is the negative log of the hydronium ion concentration and
pH = −log [H3O+]
For a solution with [H3O+] = 1 x 10−4,
pH = −log [1 x 10−4 ]
pH = [4.0]
pH = 4.0
pOH is the negative log of the hydroxide ion
pOH = -log[OH-]
pH + pOH = 14.
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

18. Example of Calculating pH
Find the pH of a solution with a [H3O+] of 1.0 x 10−3. STEP 1 Enter the [H3O+] value: Enter 1 x 103 (press 1 EE 3, then change sign) The EE key gives the exponent of 10. STEP 2 Press log key and change the sign: log (1 x 10−3) = [3] STEP 3 Make the number of digits after the decimal point (2) equal to the number of significant figures in the coefficient (2): [H3O+] = 1.0 x 10−3 pH is 3.00
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

19. Learning Check
What is the pH of coffee if the [H3O+] is 1 x 10−5 M? 1) pH = 9.0 2) pH = 7.0 3) pH = 5.0
5.0
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

20. Learning Check
The [H3O+] of tomato juice is 2 x 10−4 M. What is the pH of the solution? 1) 4.0 2) 3.7 3) 10.3
3.7
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

21. Learning Check
The [OH−] of a solution is 1.0 x 10−3 M. What is the pH? (hint = figure out pOH first) 1) ) ) –11.00
11.00
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

22. [H3O+], [OH-], and pH Values
General, Organic, and Biological Chemistry

23. Testing the pH of Solutions
The pH of solutions can be determined using
a pH meter
pH paper
indicators that have specific colors at different pH values
General, Organic, and Biological Chemistry

24. Neutralization Equations
In the equations for neutralization, an acid and a base produce a salt and water.
acid base salt water
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
H+(aq) + OH−(aq) H2O
2HCl(aq) + Ca(OH)2(aq) CaCl2(aq) + 2H2O(l)
H+(aq) + OH−(aq) H2O(l)
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

25. General, Organic, and Biological Chemistry
Antacids
Antacids
are used to neutralize stomach acid (HCl)
General, Organic, and Biological Chemistry

26. Buffers Buffers resist changes in pH from the addition of acid or base
in the body absorb H3O+ or OH from foods and cellular processes to maintain pH
are important in the proper functioning of cells and blood
in blood maintain a pH close to 7.4; a change in the pH of the blood affects the uptake of oxygen and cellular processes
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

27. General, Organic, and Biological Chemistry
Buffers (continued)
When an acid or base
is added
to water, the pH changes drastically
to a buffer solution, the pH does not change very much; pH is maintained
General, Organic, and Biological Chemistry

28. Components of a Buffer The components of a buffer solution
are acid–base conjugate pairs
can be a weak acid and a salt of its conjugate base
equal concentrations of the weak acid and the salt of its conjugate base.
Should be at reasonably high concentrations to resist changes in H+ or OH- added to the solution.
can also be a weak base and a salt of its conjugate acid
Acetic acid= weak acid
Acetate ion = conjugate base (can buy sodium acetate and mix with acetic acid in water)
General, Organic, and Biological Chemistry Copyright © 2010 Pearson Education, Inc.

29. Carbonic Acid-Bicarbonate System
Buffer system
Regulates blood pH
pH = 7.35 (vein)
pH = 7.4 (artery)
Acidosis (pH < 7.35)
Alkalosis (pH > 7.45)
Exhaling removes CO2
Kidneys secrete or reabsorb H+ and HCO3-
Metabolic acids
Lactic acid
Ketones
Phosphoric acids
Ammonium
Uric acid
Carbonic
anhydrase
CO2 + H2O H2CO H+ HCO3-

30. Summary of Buffer Action
Buffer action occurs because
the weak acid in a buffer neutralizes base
the conjugate base in the buffer neutralizes acid
the pH of the solution is maintained
General, Organic, and Biological Chemistry