Acids & Bases Section 19.1-19.2 Notes

Properties of Acids Taste sour (eg: citric acids, acetic acid) React with metals Causes blue litmus to turn pink Aqueous solutions conduct electricity

Properties of Bases Taste bitter Feel slippery (eg: soap) Causes pink litmus to turn blue Aqueous solutions conduct electricity

H2O(l) + H2O(l)  H3O+(aq) + OH-(aq) Ions in solution All water solutions contain H+ & OH- Acidic solution – contains more H+ Basic solution – contains more OH- Neutral solution – contains equal H+ & OH- Water undergoes self-ionization H2O(l) + H2O(l)  H3O+(aq) + OH-(aq) H3O+ and H+ used interchangeable to represent a hydrogen ion Pure water is neutral b/c H+ = OH-

Arrhenius Acids & Bases Swedish chemist Svante Arrhenius (1887) first proposed how acids & bases form Arrhenius model Acids – produce H+ in aq. soln. HCl(g)  H+(aq) + Cl-(aq) Bases – produce OH- in aq. soln. NaOH(s)  Na+(aq) + OH-(aq) Shortcoming: does not explain all bases (eg: NH3 = base)

Brønsted-Lowry Model Danish chemist Johannes Brønsted & English chemist Thomas Lowry proposed more inclusive model Brønsted-Lowry model Acid – H+ donor Base – H+ acceptor Every Brønsted-Lowry interaction involves conjugate acid-base pairs Conjugate acid – species produced when a base accepts H+ from an acid Conjugate base – species produced when an acid donates H+ to a base HX + H2O  H3O+ + X- acid base conjugate conjugate acid base

You try… Identify the conjugate acid/base pairs in each of the following reactions. NH4+(aq) + OH-(aq)  NH3(aq) + H2O(l) HBr(aq) + H2O(l)  H3O+(aq) + Br-(aq) Amphoteric – substance that can act as both an acid and a base CO32-(aq) + H2O(l)  HCO3-(aq) + OH-(aq) HSO4-(aq) + H2O(l)  H3O+(aq) + SO42-(aq)

Monoprotic and Polyprotic Acids Monoprotic – contains 1 ionizable hydrogen atom (HCl) Diprotic – contains 2 ionizable hydrogen atoms (H2SO4) Triprotic – contains 3 ionizable hydrogen atoms (H3PO4) Steps for ionization of a polyprotic acid: H3PO4 H2Se H2SO3

Strength of Acids Strong acids – ionize completely in water (good conductors) HCl + H2O  H3O+ + Cl- Rxn goes to completion Denoted by single arrow Weak acids – ionize only partially in water (p. 602) HC2H3O2 + H2O  H3O+ + C2H3O2- Reversible rxn (double arrow) Equilibrium established

Strength of Bases Strong base – dissociates entirely into metal ions & hydroxide ions NaOH  Na+ + OH- Weak base – ionizes only partially to form conjugate acid & hydroxide ion CH3NH2 + H2O  CH3NH3+ + OH-