Review of Acids and BasesAn acid is a substance that when dissolved in
water increases the concentration of H+
A base is a substance that when dissolved in water increases the concentration of OH-
Bronsted-Lowry Acids and BasesThese types of acid base reactions have to do with
the transfer of a proton.
The Relative Strengths of Acids and BasesWe can predict the acid or basic properties of
conjugate pairs.A strong acid produces a conjugate base that will
be very unwilling to accept a proton.A weak acid produces a conjugate base that has
some tendency to accept a proton.A substance that contains hydrogen but has
negligible acidity will produce a conjugate base that is a very strong base.
The Autoionization of Water
Calculate the concentration of H+ in a solution in which [OH-] is 0.01 M.
Calculate Ka from pHA student prepared a 0.10 M solution of formic
acid (HCOOH) and measured its pH. The pH at 25oC was found to be 2.38. Calculate Ka for formic acid.
Weak Bases Many substances behave as weak bases when
mixed with water by removing a hydrogen from the water producing OH-.
Acid-Base Properties of Salt SolutionsSolutions made from soluble salts (ionic
compounds) can be acidic or basic. We know these solutions produce anions and
cations.Many of these ions are able to react with water to
generate H+(aq) or OH-(aq). These types of reactions are often called hydrolysis.
Anions Reacting with WaterOften times an anion is the conjugate base of an
acid:
If this anion is the conjugate base of a strong acid it will have negligible tendency to remove a proton from water.
Cations Reacting with Water Polyatomic cations whose formulas contain one or
more protons are usually the conjugate acids of weak bases.
Combined Effect of Cations and Anions in SoluitonIf a solution contains two different ions that can
effect the pH differently.
Summary An anion that is the conjugate base of a strong acid (example
Br-) will not affect the pH of a solution. An anion that is the conjugate base of a weak acid (example
CN-) will cause and increase in pH. An cation that is the conjugate acid of a weak base (example
CH3NH3+) will cause a decrease in pH.
Cations of group 1A metals have no affect on pH other metals will cause a decrease in pH when a solution contains both the conjugate base of a weak acid
and the conjugate acid of a weak base the ion with the larger equilibrium constant will have the greater influence on pH.
Acid-Base Behavior and Chemical StructureWhat makes an acid or a base strong or weak?It’s chemical structure.
Binary AcidsBinary acids are ones that contain only 2 atoms
(one being H).The strength of binary acids where elements X are
in the same group decreases as the size of X increases.
OxyacidsOxyacids are ones where OH groups are attached
to a central atom.For oxyacids that have the same number of OH
groups and the same number of O atoms, acid strength increases with increasing electronegativity of the central atom.
For oxyacids that have the same central atom, acid strength increases as the number of oxygen atoms attached to that central atom increases.
Lewis Acids and BasesA Lewis base is a substance that has a free pair of
electrons.A Lewis acid is a substance that can accept that
free pair of electrons
The Common Ion EffectThe common ion effect describes what happens
when we add a strong electrolyte to a weak electrolyte solution and both compound share a common ion
ExampleWhat is the pH of a solution made by adding 0.3
mol of acetic acid and 0.3 moles of sodium acetate to enough water to make 1.0 L of solution? (Ka = 1.8 x 10-5)
Buffer SolutionsBuffer solutions are ones that resist drastic pH
changes when small amounts of strong acids or bases are added.
These solutions contain significant enough amounts of H+ and OH- that they are able to neutralize any acid or base we might add.
Buffers are usually prepared by mixing a weak acid or base with a salt of that acid or base.
Calculating the pH of a BufferWhat is the pH of a buffer that is 0.12 M lactic acid
(HC3H5O3) and 0.1 M sodium lactate (NaC3H5O)? (Ka = 1.4x10-4)
Buffer Capacity and pH RangeBuffer capacity refers to the amount of strong acid
or strong base that can be added before the pH begins to change by an appreciable amount.
pH range refers to the range of pH over which the buffer best resists pH change.
Addition of Strong Acids or Bases to BuffersAdding a strong acid or a strong base cause
opposite neutralization reactions to occur in the buffer.
ExampleA buffer is made by adding 0.3 mol of acetic acid
and 0.3 mol of sodium acetate to enough water to make 1 L of solution. the pH of the buffer is 4.74. (a) Calculate the pH of the solution after 0.02 mol of NaOH are added. (Assume that volume remains constant.)
Titration Calculations Calculate the pH when the following quantities of
0.1 M NaOH solution have been added to 50.0 mL of 0.1 M HCl
(a) 49.0 mL
(b) 51.0 mL
ExampleCalculate the pH of a solution that is formed when
45.0 mL of 0.1 M NaOH is added to 50.0 mL of 0.1 M CH3COOH. (Ka = 1.8 x 10-5)
Solubility EquilibriaWe have seen that some ionic compounds are not
soluble in water. This is only partially true.
Solubility and pHThe pH of a solution will affect the solubility of any
substance whose anion is basic.
If a compound contains an anion that is the conjugate base of a weak acid its solubility will increase as the solution becomes more acidic.
Precipitation and Separation of IonsThe equilibrium of BaSO4(s) in water can be
achieved in either direction: