Acids and Bases Three Definitions Arrhenius acid produces H + in soln base produces OH - in soln Bronsted-Lowry acid H + donor base H + acceptor in soln, dont really have free H + /protons, have H 3 O + called hydronium Three Definitions Arrhenius acid produces H + in soln base produces OH - in soln Bronsted-Lowry acid H + donor base H + acceptor Lewis acid electron pair acceptor base electron pair donor Conjugate acid-base pairs NH 3 + H 2 O NH OH - HCl + H 2 O H 3 O + + Cl - Conjugate acid-base pairs The stronger a Bronsted { }, the weaker its conjugate { }. Water can act as an acid or a base. So it can undergo autoionization. H 2 O + H 2 O H 3 O + + OH - K = K w = [H 3 O + ][OH - ] = 1.0 x Neutral: [H + ] [OH - ]= < = 1.0 x M K w = [H 3 O + ][OH - ] = 1.0 x Neutral: [H + ] [OH - ] Acidic : [H + ] [OH - ] Basic : [H + ] [OH - ] = > < = 1.0 x M [H + ] [OH - ] 1.0 x M > > < < pH Scale pH = -log [H + ] pOH = -log [OH - ] pH + pOH = 14.00 pH Scale Neutral: [H + ] = [OH - ] = 1.0x10 -7 Acidic : [H + ] > 1.0 x M Basic : [H + ] < 1.0 x M pH = 7 < 7 > 7 pH > 7 pOH < 7 pH Scale Neutral: [H + ] = [OH - ] = 1.0x10 -7 Acidic : [H + ] > 1.0 x M [OH - ] < 1.0 x M Basic : [H + ] < 1.0 x M [OH - ] > 1.0 x M pH = 7 pH < 7 pOH pOH > 7 = 7 Determine the pOH, [OH - ] and [H + ] for a solution of vinegar with pH = SIG FIGS!!! The TOTAL number of sig figs in the concentration equals the number of digits AFTER THE DECIMAL in the pH (or pOH). [H + ] = 4.93 x M pH = 9.41 BACK In ammonia, [OH-] = 4.8 x M. Calculate its pH, pOH, and [H+]. Strong Acids ionize completely memorize them!!! HCl, HBr, HI, HClO 4, H 2 SO 4, HNO 3 Weak Acids only partially ionize ALL other acids Remember acid nomenclature??? Strong Acids ionize completely. [H + ] = [HA] o memorize them!!! HCl, HBr, HI, HClO 4, H 2 SO 4, HNO 3 strong electrolytes Weak Acids only partially ionize. need ICE table to calc [H + ] ALL other acids weak electrolytes Weak Acids achieve equilibrium. soln mix contains mostly nonionized acid molecules, with some H 3 O + and conjugate base ions. (ex) HCN K a = 6.2 x Weak Acids What does the K a value tell us? K a (HNO 2 ) = 4.6 x K a (HC 2 H 3 O 2 ) = 1.8 x K a (HCN) = 6.2 x Bases Strong and weak are used in the same way to describe bases. memorize list of strong bases!!! LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH) 2 *, Sr(OH) 2, Ba(OH) 2 *borderline Bases most common weak base is NH 3 many others are a derivative of NH 3 (replace one or more hydrogens with some other group: CH 3 NH 2 ) Conjugate Acid-Base Pairs K a x K b = K w = 1.0 x NH 3 / NH 4 + K b (NH 3 ) = 1.8 x K a (NH 4 + ) = Shows mathematically that the stronger an acid, the weaker its conjugate base. 5.6 x Lactic acid (HC 3 H 5 O 3 ), which is present in sour milk, also gives sauerkraut its tartness. It is a monoprotic acid. In a 0.100M solution of lactic acid, the pH is 2.44 at 25 C. Calculate the K a for lactic acid. A student planned an experiment that would use 0.10M propionic acid, HC 3 H 5 O 2. Calculate the values of [H+] and pH for this solution. For propionic acid, K a = 1.4 x A solution of hydrazine, C 2 H 4, has a concentration of 0.25M. What is the pH of the solution? K b (C 2 H 4 ) = 1.7 x