Download Honors Chemistry Chapter 14 notes—Acids, Bases, and pH I. Acids

Honors Chemistry
Chapter 14 notes—Acids, Bases, and pH
I. Acids and Bases
A. Macroscopic Properties of Acids and Bases
1. Taste and feel— not a safe way to classify acids and bases
a. Taste
1) Acids taste sour-- Lemon juice and vinegar
2) Bases taste bitter--soap
b. Feel
1) Acids sting when placed in cuts—lemon juice in a finger cut
2) Bases feel slippery--soap
2. Acids react with bases
a. acids and bases naturally react with each other, this is central to the chemistry of living
systems, the environment, and many industrial processes.
b. acid examples—sulfuric acid (car batteries; manufacture of chemicals, fertilizer, and paper)
--phosphoric acid (soft drinks; manufacture of detergents and fertilizers)
c. base examples—lime (neutralization of acidic soil)
--ammonia (fertilizer; cleaner; manufacture of soap and chemicals)
--sodium hydroxide (drain and oven cleaners; manufacture of soap and
chemicals)
3. Litmus test and other color changes
a. acids and bases cause certain dyes to change color
b. these dyes are known as acid-base indicators
c. the most common is litmus
1) acid turns it red
2) base turns it blue
d. red cabbage is a natural acid-base indicator
4. Metals’ reactions with carbonates
a. most acids will react with metals that are more reactive than hydrogen
b. therefore acids generally speaking corrode most metals
c. generally speaking this corrosion is a single-displacement reaction (remember Chapter 6?)
d. acids will also react with carbonates (ex. CaCO3) to release CO2, water, and another
compound
e. Marble and Limestone sculptures are affected by acid precipitation
f. Bases do NOT react with carbonates.
B. Submicroscopic Behavior of Acids
1. Hydronium ion formation
a. Arrhenius definition of acid—a substance that produces hydronium ions when dissolved in
water.
b. Hydronium ion is formed when a dissociated H+ (very unstable) bonds with a water molecule
to form H3O+
2. Acidic hydrogen atoms
a. Acidic hydrogen atom—any hydrogen atom that can be transferred to water
b. There can be multiple acidic hydrogen atoms in a molecule
1) monoprotic acid—one hydrogen (HCl)
2) diprotic acid—two hydrogens (H2SO4)
3) triprotic acid—three hydrogens (H3PO4)
c. Polar bond hydrogens are usually acidic, but not always
d. Non-polar hydrogens are never acidic
3. Chemical reaction shorthand
a. reactions can be written in a short-hand manner indicating the main participants
b. HA + H2O(l)  H+(aq) + A-(aq) becomes HA(aq)  H+ + A-(aq)
c. Water is an active participant, but is left out, sort of ((aq))
d. Diprotic acids require two steps
e. Triprotic acids require three steps
4. Acids are electrolytes
a. electrolyte—any compound that conducts electricity when melted or dissolved in water
(normally caused by the presence of ions)
b. ionization—the process of forming ions
c. acids go through acid ionization forming ions; thereby becoming conductors
d. acids vary in their abilities to produce ions
C. Submicroscopic Behavior of Bases
1. Introduction
a. Arrhenius definition of base—a substance that produces hydroxide ions (OH-) when
dissolved in water
b. Bases will release hydroxide ions when placed in water.
2. Simple bases: metal hydroxides
a. a metal hydroxide consists of an ionic compound formed from a metallic cation and the
hydroxide anion.
b. metal hydroxides are soluble in water
c. the dissociation of the compound is a simple dissociation and there is no transfer between
the base and the ions like in the acid.
3. Bases that accept H+
a. Bronsted-Lowery definition of a base—a substance that accepts H+
b. Best example is probably ammonia, NH3
1) Ammonia gas dissolves in water and reacts with the water and then dissociates
2) NH3(g) + H2O(l)  NH4+(aq) + OH-(aq)
4. Bases are electrolytes
a. because bases produce ions their solutions will conduct electricity
b. as with acids, the ability to dissociate is variable; therefore, not all bases conduct equally
5. Why does water transfer H+ to bases?
a. Example: ammonia is a polar molecule and the nitrogen end is slightly negative; this end
attracts the H+ from the polar water molecule.
b. bottom line any polar base will attract the H+ from the polar water molecule
D. Other Acids and Bases: Anhydrides
1. Introduction
a. anhydrides—compound that reacts with water to form an acid or a base (the water is
“removed”
b. this is based on an oxide, either metal or non-metal oxides
2. Acidic anhydrides
a. non-metal oxides will react with water to form an acid
b. CO2 is the most familiar, it reacts with water to form carbonic acid (H2CO3)
c. Obviously atmospheric CO2 will cause rain to be acidic; however, this is normal and not
detrimental to the environment
d. other anhydrides (sulfur oxides and nitrogen oxides) can put the acid rain out of balance
1) Sources of sulfur oxides
a) burning of sulfur-containing coal in power plants
b) sulfur dioxide, SO2 is released and reacts with oxygen to form sulfur trioxide (SO3)
2) Sources of nitrogen oxides
a) exhaust from automobiles because of the high temperatures
b) this is the major source
3. Basic anhydrides
a. metal oxides will react with water to release OHb. Lime (CaO) reacts with water to form Calcium hydroxide (Ca(OH)2)
c. Metal oxides are major components in ash, which when put into solution is called lye
1) this is mixed with animal fat to form soap
2) Na2O is one of the major metal oxides in this process.
E. The Macroscopic-Submicroscopic Acid-Base Connection
1. Acid examples
a. lemons
b. tomatoes
c. vinegar
d. coffee
e. tea
2. Base examples
a. oven cleaner
b. soap
c. bleach
d. antacids
II. Strengths of Acids and Bases
A. Strong acids and bases
1. Strong bases
a. defined—a base that completely dissociates when dissolved in water
b. best example is NaOH
c. a good example is Ca(OH)2
d. based on the percentage of formula units that dissociate of those that dissolved
e. Table 14.3 gives a list
2. Strong acids
a. defined—an acid that completely ionizes in water
b. best example is HCl
c. a good example is H2SO4
d. based on the percentage of formula units that dissocate of those dissolved
e. Table 14.3 gives a list
B. Weak acids and bases
1. Weak acids
a. defined—an acid that only partially ionizes in water
b. CH3COOH (acetic acid (ethanoic acid)) is a good example, only .5% ionizes
c. the structure of the molecule determines the extent to which the acid ionizes
2. Weak bases
a. defined—a base that only partially ionizes in water
b. NH3 (ammonia) is a good example, only .5% ionizes
3. Weak is not insignificant
a. many living systems are based on weak acid-weak base interactions
b. amino acids and DNA structure are included in this
4. Strength is not concentration
a. Concentration uses terms like dilute and concentrated—this indicates the concentration or
how much acid or base is present
b. Strength is dealing with how much actually ionizes
C. The pH scale
1. Introduction—pH scale was developed by Soren P. L. Sorenson in 1909
2. What is pH?
a. it is a mathematical scale in which the concentration of hydronium ions in a solution is
expressed as a number from 0 to 14.
b. this scale is easier to work with than the actual concentrations that range from
1 x 100 to 1 x 10-14
c. pH = -log[H3O+] (the negative log of the hydronium ion concentration)
d. a concentration of 2.0 x 10-5 will yield a pH of 4.7
3. Relating hydronium ions to hydroxide ions
a. [H3O+][OH-] = 1 x 10-14 The hydronium ion concentration times the hydroxide ion
concentration equals 1 x 10-14
b. pOH = -log[OH-]
c. pH + pOH = 14
4. Neutral solutions
a. the [H3O+] and the [OH-] are equal (1 x 10-7)
b. this corresponds to a pH of 7
5. Interpreting the pH scale
a. 3 general areas
1) 0-7  acid
2) 7  neutral
3) 7-14  base
b. as the pH decreases the hydronium ion concentration increases and the hydroxide ion
concentration decreases
c. as the pH increases the hydronium ion concentration decreases and the hydroxide ion
concentration increases
d. this change is 10 fold change for each level on the pH scale
6. pH of common substances
--figure 14.23 on page 503 gives the pHs of some common materials