Acid-Base Properties and Theories Chemistry 12/12AP

Properties of Acids Sour taste Turn blue litmus red (and other indicators) Neutralize bases Conduct electricity (electrolytes) React with active metals (group I, II) to produce H2 gas React with metal oxides to produce a salt of the metal and water Produce H+ or H3O+ in solution (see acid-base theories) pH less than 7

Properties of Bases Bitter taste ex. tonic water (quinine) Turn red litmus blue (and other indicators) Neutralize acids Conduct electricity (electrolytes) Feel slippery (soapy) pH greater than 7 Produce OH- in solution

Arrhenius Theory An Acid is a substance that produces H+ ions in solution. A base is a substance that produces OH- ions in solution. Neutralization occurs when H+ ions combine with OH- ions to form water.

Acid or Base (Arrhenius Style) H2SO4 Ca(OH)2 Pb(NO3)2 NaHCO3 NaOH HBr

Limitations of Arrhenius Theory Acids (like HCl) are able to be neutralized by NaOH and NH3. Not all bases have OH- ions, NH3 in H2O does, but, if NH3 reacts as a gas with HCl gas, NH4Cl is still formed, but is not a solution, so this theory won’t always work.

Bronsted-Lowry Theory An acid is a proton donor. A base is a proton acceptor. H3O+ is a hydronium ion (aka. THE PROTON) H2O is the base. HCl is the acid

Writing Conjugates See Board notes

Conjugate Acid-Base Pairs A conjugate acid is the substance that has accepted the proton (gained an H+) A conjugate base is the substance that has lost the proton. Each acid has a conjugate base and each base has a conjugate acid.

Formation of Acids Acids are formed when a non-metal oxide is dissolved in water (forms an oxyacid) SO2 + H2O  H2SO3

Acid Nomenclature

Formation of Bases Formed when a metal oxide reacts with water (forms a strong base) Na2O + H2O 2NaOH

Relative Strengths of Acids and Bases

Strong Acids & Bases Strong acids – hydrogen halides, oxyacids of halogens, sulfuric acid & nitric acid Strong bases – NaOH, KOH, Cs(OH)2, Ca(OH)2 Both of these ionize completely in H2O.

Weak Acids & Bases Weak acids and bases do not ionize completely in water A weak acid/base will be shown with a double arrow reaction, and also have small Ka and Kb values

Self-ionization of Water

Ionization Constants Acid ionization constant (Ka) Base ionization constant (Kb) Magnitude dictates the strength of the acid Strong acids have large Ka values – this means that they dissociate completely (100%)  Weak acids have small Ka values – and do not dissociate completely (usually 5% or so)  Magnitude dictates the strength of the base Strong bases have large Kb values – and dissociate completely (100%)  Weak bases have small Kb values - and do not dissociate completely (5% or so) 

Ion Product of Water (Kw) Kw = 1.0 x 10-14=[H+][OH-] – changes with temperature Kw = Ka x Kb Uses: Can find concentration of OH- or H+, the Kb of the conjugate base (and vice versa), or used with pH or pOH calculations when necessary

pH and pOH pH = -log10[H+] or pH = -log10[H3O+] (same thing) [H+] = 10-pH pOH = -log10[OH-] [OH-] = 10-pOH

pH Scales

Ionization Constants of Weak Acids & Bases

Equilibrium Problems Using Acids Type 1: Solving for Ka You must have the following: - the equation for the reaction - the equilibrium expression - the concentrations at equilibrium (ICE chart) - The concentrations at equilibrium are usually found with pH or a % ionization.

Equilibrium Problems Using Acids Type 2. Solving for EQ amounts You must have the following: - the reaction - the equilibrium expression and Ka value - the initial concentration of the acid (in mol/L) - With this type, it may ask for the pH at equilibrium