Chap 14 Acids and Bases

Acids vs Bases Acids Taste sour Strong reaction with metals pH < 7 Red in litmus Clear in phth Produces H+ (Arrhenius) Proton donor (Bronsted Lowry) Bases Taste bitter Feel slippery Weak reaction with metals pH > 7 Blue in litmus Pink in phth Produces OH- (Arrhenius) Proton acceptor (Bronsted Lowry)

Conjugates Conjugate base – everything that remains of acid molecule after proton lost Conjugate acid – formed when proton transferred Conjugate acid-base pair – two substances related to each other by donating and accepting a proton HA(aq) + H2O (l) ⇆ H3O+ (aq) + A- (aq) acid base conjugate conjugate acid base B (aq) + H2O (l) ⇆ BH+ (aq) + OH- (aq) base acid conjugate conjugate acid base

Acid Base Equilibria Must consider the reaction Need a reaction for every equilibrium Need to write a K expression Need to determine the major species involved – what makes up the solution Need to know what ions breaks up into – or dissociates into If more than one possible, look to K values to see which is more influential (important to problem) Larger K = more important May need to use Ice method if looking for equilibrium concentrations, as long as have initial to start.

Dissociation Acids/bases dissociate easily – breakdown into ions Ka/Kb= dissociation constant = equilibrium constant for acid/base HA(aq) ⇆ H+(aq) + A-(aq) Ka = 𝐻+ [𝐴−] [𝐻𝐴] Kb = 𝐵𝐻+ [𝑂𝐻−] [𝐵] Large K = strong acid/base; equilibrium lies to the right (dissociates well or completely) Small K = weak acid/base; equilibrium lies to the left (dissociates slightly) Tables of Ka and Kb values – A22 & A23 B (aq) + H2O (l) ⇆ BH+(aq) + OH-(aq)

Water Considered to be amphoteric - can be either acid or base Autoionizes (self-ionization) H20 (l) + H2O (l) ⇆ H3O+ (aq) + OH- (aq) acid base acid base Dissociation constant for water: Kw = [H3O+][OH-] Kw = 1.0 x 10 -14 @ 25°C ** Kw changes as the temperature changes (Increases as the temperature increases)

pH What is it? measure of the [H+] (measures solution acidity) Based on log scale base 10 - changes by 1 for every power of 10 pH scale: 0 -14 Acidic (0-6) Neutral (7) Basic (8-14) Strong at ends; weak closer to 7 p.661 for chart

Calculating with pH pH = -log[H+] pOH = -log[OH-] [H+] = 1.0 x 10 –pH pK = -log(K) Kw = [H+][OH-] pH + pOH = 14 If [H+] = [OH-], neutral If [H+] > [OH-], acidic If [H+] < [OH-], basic

Example calc pH of water = 7 So [H3O+] = 1.0 x 10-7 and [OH-] = 1.0 x 10-7 pH + pOH = 14 7 + 7 = 14 Kw = [H3O+][OH-] = 1.0 x 10-7 *1.0 x 10-7 Kw = 1.0 x 10-14

Polyprotic Acids Have more than 1 proton (more than 1 H in formula) Diprotic = 2 H’s Triprotic = 3 H’s Dissociates in a stepwise process – more than one step, one proton (H) at a time Has more than 1 Ka value (Ka1, Ka2, Ka3, etc) First value is largest – most important get smaller as go - acid gets weaker as remove H’s H3PO4 (aq) ⇆ H+ (aq) + H2PO4- (aq) H2PO4- (aq) ⇆ H+ (aq) + HPO42- (aq) HPO42- (aq) ⇆ H+ (aq) + PO43- (aq)

Acid Base Properties Standard neutralization reaction: Acid + Base ⇆ Water + Salt Strong acid + strong base = neutral Strong acid + weak base = acidic Weak acid + strong base = basic