ACIDS AND BASES
A. Properties of Acids and Bases
1. Acids --> sour taste, electrolytes, react with metals, change indicator colors, react with bases to form water and salt
a. Ex. --> vinegar, citric fruits
2. Bases --> bitter taste, slippery, electrolytes, change indicator colors, react with acids to form water and salt
a. Ex. --> soap, "pepto"
B. Naming and Formulas of Acids and Bases
1. ACID -- a compound that produces hydrogen ions when dissolved in water
a. General formula --> HX (X = anion, mono- or polyatomic)
2. Rules for naming acids:
a. When anion name ends in -ide, the acid name begins with hydro-. The stem of the anion has the suffix -ic and followed by "acid"
b. When anion name ends in -ite, the acid name is the stem and has the suffix -ous and followed by "acid"
c. When anion name ends in -ate, the acid name is the stem and has the suffix -ic and followed by "acid"
3. Reverse direction to write formulas
4. BASE -- a compound that produces hydroxide ions when dissolved in water
a. General formula --> XOH (X = cation, mono- or polyatomic)
b. Naming rules same as ionic compounds
II. Hydrogen Ions and Acidity
A. Hydrogen Ions from Water
1. Water molecules can collide with enough energy to transfer a hydrgogen ion
a. One molecule becomes a negative hydroxide ion
b. One molecules becomes a positive HYDRONIUM ION (H3O+)
1. Hydronium ion = Hydrogen ion
c. SELF-IONIZATION of water
d. Pure water, self-ionization is very snall
1. Hydrgogen ion concentration [H+] = 1.0 x 10(-7) M
2. Hydroxide ion concentration [OH-] = 1.0 x 10(-7) M
3. [H+] = [OH-] --> Neutral solution
2. Ion concentration depends on each other
a. Increase one ion concentration, then the other must decrease
b. Ion-Product Constant for Water (Kw)
[H+]x[OH-] = {1.0 x 10(-7) M} x {1.0 x 10(-7) M} = 1.0 x 10(-14) M2 = Kw
3. If a substance is dissolved and releases Hydrogen ions, then [H+] > [OH-]
a. [H+] > 1.0 x 10(-7) M --> acidic solution
4. If a substance is dissolved and releases Hydroxide ions, then [H+] < [OH-]
a. [H+] < 1.0 x 10(-7) M --> basic solution (alkaline solution)
B. The pH concept
1. Simpler method for expressing [H+] values under 1.0 M
a. Range is from 0-14 with 7 = neutral, 0 = strong acid, 14 = strong base
b. Determined by taking the negative logarithm of the [H+]
1. pH = -log[H+] ; pOH = -log[OH-] ; pH + pOH = 14
acidic solution pH < 7 [H+] > 1 x 10(-7) M
neutral solution pH = 7 [H+] = 1 x 10(-7) M
basic solution pH > 7 [H+] < 1 x 10(-7) M
C. Calculating pH values
1. Not all pH values are whole numbers
2. You must use a logarithm table (App. B) or a calculator
3. Concentrations can be calculated from pH values
a. Use logarithm table or calculator to do antilog
D. Measuring pH
1. Acid-Base Indicators -- is an acid or base that undergoes dissociation in a known pH range with a color change
HIn(aq) <--> H+(aq) + In-(aq)
Acid form Base form
In = Indicator
a. Shows you an approximate change over a short pH range (ex. on page 590)
b. Can be affected by temperature change or solts in solution
2. pH paper (litmus, universal indicator)
a. Paper dipped in solution and compared to a color chart
3. pH meter -- electronic device used to make rapid, accurate measurements
a. Accurate (0.01 of actual pH)
b. Not affected by temperature change or salts in solution
III. Acid-Base Theories
A. Arrhenius Acids and Bases
1. acids are hydrogen-containing compounds that ionize to yield H+ ions in aqueous solutions
a. Ex.: HCl --> H+ + Cl-
2. bases are compounds that ionize to yield OH- ions in aqueous solutions
a. Ex.: NaOH --> Na+ + OH-
3. Monoprotic acids -- contain one ionizable hydrogen (HCl)
4. Diprotic acids -- contain two ionizable hydrogens (H2SO4)
5. Triprotic acids -- contain three ionizable hydrogens (H3PO4)
6. Not all hydrogens will ionize
a. If hydrogen is part of a strong polar bond, it will ionize
b. If hydrogen is part of a weak polar bond, it will not ionize
B. Bronsted-Lowry Acids and Bases
1. Acids are hydrogen-ion donors
2. Bases are hydrogen-ion acceptors
3. Arrhenius doesn't include all acidic and basic compounds --> need new theory
a. Ammonia, sodium carbonate
1. NH3 + H2O <--> NH4+ + OH-
H-ion H-ion solution is basic
acceptor donor
b. The reverse reaction also has an acid and base, therefore...
NH3 + H2O <--> NH4+ + OH-
base acid conjugate conjugate
acid base
1. NH4+ acts as an acid (Conjugate acid -- particle formed when a base gains a H+ ion)
2. OH- acts as a bae (Conjugate base -- particle remaining when an acid donates H+ ion)
4. Conjugate Acid-Base Pair -- two substances related by the loss or gain of a H+ ion
a. NH3 and NH4+ ; H2O and OH-
5. Amphoteric -- a substance that can act as an acid or a base (H2O)
C. Lewis Acids and Bases
1. acids accept a pair of electrons to form a covalent bond
2. bases donate a pair of electrons to form a covalent bond
3. Lewis theory corresponds to Bronsted-Lowry Theory
Theory Acid Base
Arrhenius H+ producer OH- producer
Bronsted-Lowry H+ donor H+ acceptor
Lewis electron pair acceptor electron pair donor
IV. Strengths of Acids and Bases
A. Strong and Weak Acids and Bases
1. Strength depends on degree of ionization
2. Strong acid -- completely ionizes in aqueous solution
3. Weak acid -- partially ionizes in aqueous solution
4. Strong base -- completely dissociates into metal ions & hydroxide ions in aqueous solution
5. Weak base -- partially dissociates into metal ions & hydroxide ions in aqueous solution
Strong Acid (pH = 0) Weak Acid (pH = 6)
Hydrochloric acid Nitric acid Sulfuric acid Acetic acid Carbonic acid
Weak Base (pH = 8) Strong Base (pH = 14)
Ammonia Calcium hydroxide Sodium hydroxide Potassium hydroxide
Outline based upon:
Matta, M. S., Staley, D. D., Waterman, E. L., & Wilbraham, A. C. (2000). Chemistry, Addison-Wesley. (5th ed.). Menlo Park, CA: Prentice Hall, pp. 577-608.
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