properties of acids electrolytes: conduct electricity react to form salts change the color of an...
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Properties of acids
• Electrolytes: conduct electricity
• React to form salts
• Change the color of an indicator
• Have a sour taste
Properties of Bases
• Bitter taste
• “slippery feel”
• Electrolyte
• React with an acid to form a salt
Arrhenius Acids and Bases
• An acid contains a Hydrogen ion that easily disassociates
• A base has a hydroxide ion that easily disassociates
Bronsted-Lowry
• An acid is a hydrogen ion donor
• A base is a hydrogen ion acceptor.
• NH3(aq)+ H2O(aq) NH4+
(aq) + OH-(aq)
• Base Acid Conj. Acid Conj. Base
conjugate acids and bases
• These are the reverse reaction “reactants”
• HA(aq) + H2O(l) H3O+(aq) + A-
(aq)
• Acid Base conjugate conjugate
acid base
• HCl + NaOH HOH + Cl-
Lewis acid and bases
• An acid is an electron pair acceptor
• A base is an electron pair donator
base acid• NH3 + BF3 H3N BF3
Acid Strength
A strong acid is one for which the equilibrium lies far to the products side Ka > 1.
A weak acid is one for which the equilibrium lies far to the reactants side Ka < 1.
Table 14.1 on page 659.
Oxyacids
• Acids where the acidic hydrogen is attached to an oxygen.
• Pictures on pages 658-659.
• Structural formulas given in table 14.8 on page 694.
Organic acids
• Acids with a carbon atom backbone.
• Commonly contain a carboxyl group.
• Acetic acid
• Benzoic acid
Autoionization of water
• H2O + H2O H3O+ + OH-
• Kw = [H3O+] [OH-] = 1.0 x 10-14
• [H3O+] [OH-] = [H+] [OH-]
• [H+] = [OH-] =1.0 x 10-7 M
• pH = -log [H+]• [H+] = antilog (-pH)
• pOH = -log[OH-]• pK = -log K
• Significant figures in logarithms- the # of decimal
places in the log = # of sig figs in the original number.
System for solving weak acid equilibrium problems
• List the major species in solution.
• Find any species that can produce H+ and write a balanced equation for the reaction producing H+.
• Use the values for K for the reactions you have written to decide which reaction will dominate.
• Write the equilibrium expression for the dominant reaction.
• List the initial concentrations of the species in the dominant reaction.
• Define the change needed to obtain equilibrium. Define x.
• Write equilibrium concentrations in terms of x.
• Put equilibrium concentrations into equilibrium expression.
• Solve for x the “easy way”• Use the 5% rule to see if
approximation is valid.• Calculate [H+] and pH.
• Calculate the pH of a solution that contains 1.00M HCN and 1.00M HNO2. Also calculate the concentration of cyanide ions.
% dissociation
• = amount dissociated x100
• initial concentration
• For a given weak acid, the % dissociated increases as the acid becomes more dilute.
• In a 0.100M solution, lactic acid (HC3H5O3)is 3.7% dissociated. Calculate the value of Ka for this acid.
Bases
• Strong bases – hydroxides of group 1A metals and calcium, barium and strontium.
• Weak bases are commonly ammonia and substituted ammonia compounds.
• Table 14.3 on page 678.
Salts that produce neutral solutions
• Salts that consist of the cations of strong bases and the anions of strong acids have no effect on pH.
• KCl, NaNO3 , Ba(HSO4)2
Salts that produce basic solutions
• Salts that consist of cations of strong bases and the anion is the conjugate base of a weak acid.
• NaC2H3O2, KNO2, Sr(CN)2
Salts that produce acidic solutions• Salts that consist of a cation that
is the conjugate acid of a weak base and the anion of a strong acid.
• NH4Cl• A salt that contains a highly
charged metal ion. AlCl3 see sample exercise 14.20.
• If the anion is the conjugate base of a weak acid and the cation is the conjugate acid of a weak base the Kb must be compared to the Ka. Which ever is greater will dominate.
Effect of structure on acid-base properties
Acidic properties depend on two factors: H-X
• The strength of the bond . As the strength increases the acidity decreases
• The polarity of the bond. As polarity increases acidity increases
Strength of oxyacids
• Within a series of oxyacids as the number of oxygens increases the strength of the acid also increases.
• Table 14.8 page 694
Acid-base properties of oxides• Depends on the electronegativity of
the element bonded to oxygen. O-X
• Non-metal oxides in water will form acids. O-X is stronger than H-O in polar water.
• Metal oxides in water form bases. O-H stronger than O-X in polar water.
Common Ion Effect
• The shift in equilibrium position because of the addition of an ion already involved in the equilibrium.
• Equilibrium shifts away from the added component.
Buffered Solutions
• Resists change in pH when either hydrogen or hydroxide ions are added.
• Consist of a solution that contains both a weak acid and its salt or a weak base and its salt.
Important Characteristics are on page 726.
Buffer Capacity
• Represents the amount of hydrogen or hydroxide ions the buffer can absorb without a significant change in pH.
• Best buffers contain a weak acid with a pKa as close as possible to the desired pH.