Chemistry 1032 Chapter 15 Acids and Bases 15 2 The Nature of Acids and Bases Acids o Acids have the following general properties A sour taste The ability to dissolve many metals The ability to turn blue litmus paper red The ability to neutralize bases o Carboxylic Acid An acid containing a carboxyl group An organic functional group R Group consisting of a carbon atom double bonded to an oxygen atom and single bonded to a hydroxyl group Carboxyl Group Example of a Carboxylic Acid o Some common acids Hydrochloric Acid HCl Sulfuric Acid H2SO4 Nitric Acid HNO3 Acetic Acid HC2H3O2 Citric Acid H3C6H5O7 Carbonic Acid H2CO3 Hydrofluoric Acid HF Phosphoric Acid H3PO4 Bases o Bases have the following general properties A bitter taste A slippery feel The ability to turn red litmus paper blue The ability to neutralize acids o Alkaloids o Some common bases organic bases found in plants that are often poisonous Sodium Hydroxide NaOH Potassium Hydroxide KOH Sodium Bicarbonate NaHCO3 Sodium Carbonate Na2CO3 Ammonia NH3 15 3 Definitions of Acids and Bases 3 Different definitions of acids and bases o 1 The Arrhenius Definition o 2 The Br nsted Lowry Definition o 3 The Lewis Definition The Arrhenius Definition o Acid A substance that produces H ions in an aqueous solution o Base A substance that produce OH ions in an aqueous solution o Hydronium Ion H3O ion A result of H ions associating with H2O molecules H ions always associates with H2O molecules to form hydronium ions and other associated species with the general formula H H2O n o Example of an Arrhenius Base NaOH is an Arrhenius base because it produces OH ions in a solution When NaOH is added to water it dissociates or breaks apart into its component ions o Under the Arrhenius definition acids and bases combine to form water The Br neutralizing each other in the process nsted Lowry Definition o This definition focuses on the transfer of H ions in an acid base reaction o Acid Proton donor o Base Proton acceptor o This definition more clearly shows what happens to the H ion from an acid it o Amphoteric o Conjugate Acid Base Pair associates with a water molecule to form a hydronium ion a proton Substances that can act as an acid or a base water Two substances related to each other by the transfer of o Summarizing Acid Base reactions under the Bronsted Lowry definition A base accepts a proton and becomes a conjugate acid An acid donates a proton and becomes a conjugate base 15 4 Acid Strength and the Acid Ionization Constant K a The strength of an electrolyte is determined by the extent of the dissociation of the electrolyte into its component ions in a solution o A strong electrolyte Completely dissociates into ions in a solution o A weak electrolyte Only partially dissociates Therefore o A strong acid o A weak acid Completely ionizes in a solution Partially ionizes in a solution The strength of an acid depends on the equilibrium General Equation for Acid Ionization Strong Acids aq H2O l H3O aq A o HA o If the equilibrium lies far to the right the acid is strong aq It s virtually completely ionized o If the equilibrium lies far to the left the acid is weak It is only partially ionized o Acids that are either entirely or almost entirely ionized o Monoprotic Acids Contain only one ionizable proton o Diprotic Acids Contain two ionizable protons o Examples of Strong Acids Hydrochloric Acids HCl Hydrobromic Acid HBr Hydroiodic Acid HI Nitric Acid HNO3 Perchloric Acid HClO4 Sulfuric Acid H2SO4 Diprotic Acid Weak Acids o Does not completely ionize in a solution o The degree to which an acid is strong or weak depends on the attraction between the anion of the acid the conjugate base and the hydrogen ion o Looking at the equation aq H2O l H3O aq A HA The degree to which the following reaction proceeds in the forward direction depends on the strength of the attraction between H and A If the attraction between H and A is strong It favors the reverse direction aq The acid is weak If the attraction between H and A is weak It favors the forward direction The acid is strong o Examples of Weak Acids Hydrofluoric Acid HF Acetic Acid HC2H3O2 Formic Acid HCHO2 Sulfurous Acid H2SO3 Diprotic Carbonic Acid H2CO3 Diprotic Phosphoric Acid H3PO4 Triprotic a o The Acid Ionization Constant K Acid Ionization Constant The way we quantify the relative strengths of weak acids The acid ionization constant is the equilibrium constant for the ionization reaction of a weak acid in water The Weak Acid Equilibrium Constant The smaller the constant the further to the left the equilibrium point for the ionization reaction lies and the weaker the acid The larger the constant the further to the right the equilibrium point for the ionization reaction lies and the strong the acid 15 5 Autoionization of Water and pH o Water is amphoteric meaning it can act as an acid or base Even in pure water water acts as an acid and a base with itself This process is called autoionization o The equilibrium constant for the autoionization reaction of water o 14 o K w 1 0 x 10 ALWAYS o Types of solutions Neutral Acidic Basic pH log H Sig figs Logarithms 3O Concentrations of H3O and OH are equal Concentration of H3O is greater than concentration of OH Concentration of OH is greater than concentration of H3O o The pH Scale A Way to Quantify Acidity and Basicity Only the numbers to the right of the decimal point are significant in a logarithm If the original number had 3 sig figs the log would be reported to 3 decimal places In general at 25 C o pOH and Other p scales pH 7 The solution is acidic pH 7 The solution is basic pH 7 The solution is neutral OH instead of H3O pOH log OH The relationship between pH and pOH The pOH scale is analogous to the pH scale but is defined with respect to The sum of pH and pOH is always equal to 14 00 at 25 C pH pOH 14 00 Another common p scale is pKa defined as follows a logKa pK The pKa of a weak acid is just another way to quantify its strength The smaller the pKa the stronger the acid o Example Ka of Chlorous Acid is 1 1 x 10 2 and pKa of 1 96 Ka of Formic Acid is 1 8 x 10 4 and pKa of 3 74 Therefore Chlorous acid is a stronger acid 15 6 Finding the H 3O and pH of Strong and Weak Acid Solutions o There are two potential sources of H3O The acid itself The ionization of water The ionization of water contributes a negligibly small amount of H3O compared to the ionization of a strong or weak acid Therefore it is not included in any mathematical work we do o Strong Acids The