8.1 Understanding Acids and Bases
Properties of Acids and Bases
Acids- (Arrhenius Theory definition) A compound that ionizes in water to form
hydrogen ions (H+)
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Sour tasting, water-soluble substances
Very reactive and can combine with many other substances
Very good conductors of electricity when dissolved in water
Must be treated with care because they are corrosive
Chemical formulas begin with Hydrogen
Turn blue litmus paper red
Neutralize bases
React with metals to produce hydrogen gas
Some metals react with acids to produce Hydrogen Gas
Zinc (s) + Hydrochloric acid ---- Hydrogen (g) + Zinc chloride
Acid reacts with compounds that contain carbonate and hydrogen carbonate
(bicarbonate) groups
Bases - (Arrhenius Theory definition) An ionic hydroxide (OH) that dissociates in
water to produce hydroxide(OH-) ions
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Bitter-tasting, water-soluble substances
Feel slippery when dissolved in water
Good conductors of electricity when dissolved in water
Often described as alkaline
React with Proteins and break them down into smaller molecules
Formulas end in OH
Table 1 shows
 Pure liquid samples of bases and ionic compounds conduct electricity
 Aqueous solutions of Ionic compounds, Bases and Acids conduct electricity
 Acids do not conduct electricity in their pure states (solid or liquid) but do
conduct electricity in their aqueous state
Acids Ionize in water to produce H+
Ionization
 A reaction in which electrically neutral molecules (or atoms) produce ions
 When an acid molecule reacts with water a proton (H+ ion) is transferred
from the acid molecule to a water molecule leaving behind the rest of the acid
molecule as an anion (negative non-metal ion)
 For acids assume that they are aqueous unless otherwise stated
 Example
Ionization equation: HCl(g) + H2O(l) -> H3O+(aq) + Cl-(aq)
Chemists simplify the ionization equation by canceling out a water
molecule from both sides of the equation to produce the simplified net
ionic equation
Simplified Ionization Equation: HCl(g) -> H+(aq) + Cl-(aq)
Bases Dissociate in water to produce OHDissociation reactions
 When ionic compounds separate into their positive and negative ions
 Example
o NaCl(aq) --> Na+ + Clo Ba(OH)2 
Ba2+ + 2OH-
Sample problem
Write dissociation or ionization equations for the dissolving of the following chemicals
in water
a.
Potassium Chloride
b. Hydroiodic acid
Types of acids
Strong acids
 An acid that ionizes almost completely (>99%) in water to form
aqueous hydrogen Ions
 Ex. Sulfuric acid, Nitric acid, hydrochloric acid
Weak Acids
 An acid that ionizes only partially (< 50%) in water to form aqueous
Hydrogen ions
 Example Carbonic acid, acetic acid and nitric acid
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To communicate the percentage ionization and the strength of an acid we write the
Percentage ionization over the chemical equation arrow
Sample problem
The following acidic solutions were tested (at equal concentration and temperature) for
electrical conductivity. Write ionization equations to explain the relative conductivity of
each acid
a. Hydrobromic acid (aqueous hydrogen bromide): high conductivity
b. Hydrofluoric acid (aqueous hydrogen fluoride): low conductivity
Hydrochloric, nitric, and sulfuric acid are strong. At this point assume all others
are weak
Also assume all bases are hydroxides and strong.
8.2 pH of a Solution
pH is a way of indicating the concentration of hydrogen ions present in a solution.
Concentration is the amount of a substance (moles) in a given volume of solution.
Molar concentration of H+ ions is extremely important in chemistry. The higher the
concentration of H+ ions the more acidic a solution is.
Any aqueous solution can be classified as acidic, neutral, or basic using a scale based on
the hydrogen ion concentration. Square brackets [ ] around an element, molecule, or ion
indicate Molar concentration (mol/L)
Neutral solution, [H+(aq)] = 1 x 10-7 mol/L = a pH of 7
Acidic Solution, [H+(aq)] > 1 x 10-7 mol/L = a pH of 0 - 6.99
Basic Solution, [H+(aq)] < 1 x 10-7 mol/L = a pH of 7.1 – 14
[H+(aq)] = 10-pH
Example
pH of 2 is the same as a [H+(aq)] of 1 x 10-2 mol/L
[H+] of 1 x 10-11 means pH is 11.
When pH changes by one unit [H+(aq)] changes by a factor of ten.
Example
pH changes from 5 to 6 the Hydrogen ion concentration has been decreased by a
factor of ten (10-5 to 10-6)
How much more acidic is a pH of 2 than a pH of 5?
pH can be changed by dilution
 If pH changes by one unit the [H+] concentration has decreased by a factor of 10
 If the [H+] concentration changes by a factor of 100 pH changes by a factor of 2.
 Dilute an acid pH increases dilute a base pH decreases
Sample problem
What is the pH of each of the following solutions?
a.
1 x 10-2 mol/L hydrogen ion concentration in Vinegar (HC2H3O2)
b. [H+(aq)] = 1.0 x 10-12 mol/L in household ammonia
Sample problem
What is the Hydrogen ion concentration for the following solutions?
a. A carbonated beverage with a pH of 3.0
b. An antacid solution for which pH = 10.00
Neutralization
 A reaction between an acid and a base that results in a pH closer to 7
 Acid + Base  Ionic salt + Water
 Removing H+ ions is much more effective at changing pH than dilution.
 Diluting a solution makes it less hazardous but neutralizing is more effective.
Calculating PH and Hydrogen Ion Concentration
pH = -log10[H+]
[H+] = 10-pH
Sample problem
An antacid solution has a hydrogen ion concentration of 4.7x10-11 mol/L.
What is its pH?
Sample Problem
The pH reading of a solution is 12.22. What is the hydrogen ion
concentration?