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ANNOUNCEMENTS Arnold Orville Beckman (April 10, 1900 May 18, 2004) Invented the pH meter in 1934 (because of lemons!) Founded Silicon Valley (located in Palo Alto so that it was near his friends aging mother) Was a Marine in WWI Slide 2 Water autoionization Slide 3 Slide 4 pH and pOH calculations What is the pH of [H 3 O + ] = 4.6 x 10 -5 ? What is the pOH of [OH - ] = 3.3 x 10 -4 ? What is the pOH of [H 3 O + ] = 4.6 x 10 -5 ? What is the [H 3 O + ] when the pH = 4.2? [H 3 O + ][OH - ] = 1.0 x 10 -14 pH = -log[H 3 O + ] pOH = -log[OH - ] [H 3 O + ] = 10 -pH [OH - ] = 10 -pH pH + pOH = 14.00 Slide 5 [H 3 O + ]pH [OH - ]pOH pH+pOH=14 [H 3 O + ]][OH - ]=10 -14 The pH Square Slide 6 What is the pH when [H 3 O + ] = 0.045 M? 1. 0.045 2. 13.995 3. -1.35 4. 1.35 Slide 7 What is the pH when [OH - ] = 6.5 x 10 -4 M? 1. 3.18 2. -3.18 3. 10.81 4. 15.18 Slide 8 What is the [OH-] when pH = 5.84 M? What is the [OH - ] when pH = 5.84 M? 1. 1.45 x 10 8 2. 3.31 x 10 -6 3. 6.92 x 10 -9 4. 5.84 Slide 9 Strong acids and bases ionize completely Strong monoprotic acids [H 3 O + ] = [acid] Strong diprotic acid [H 3 O + ] = 2[acid] Strong monoprotic base [OH - ] = [base] Strong diprotic base [OH - ] = 2[base] Slide 10 Calculating the pH of a strong acid solution What is the pH of a 0.150 M solution of HCl? Slide 11 Changing the pH of a solution is harder the farther away you are from neutral pH How much acid does it take to go from pH=1 to pH=2? How much acid does it take to go from pH=5 to pH=6? HCl molar mass=36.46 g/mol Slide 12 What is the real range of pHs that are possible? Can pH be zero? Can pH be negative? Can pH be greater than 14? Slide 13 Conjugate Acid-Base Pairs Different definitions of acids and bases Brnsted-Lowry Acid = H + (proton) donor Base = H + (proton) acceptor Acid-base reaction involves proton transfer Conjugate acid/base = what is left on the other side after the proton has been transferred AcidConjugate base HFF-F- NH 4 + NH 3 Slide 14 What is the conjugate base of CH 3 CO 2 H? 1. CH 3 CO 2 H 2 2. CH 3 CO 2 - 3. CH 3 CO 3 Slide 15 What is the conjugate acid of HPO 4 2-? What is the conjugate acid of HPO 4 2- ? 1. H 2 PO 4 - 2. H 3 PO 4 3. PO 4 3- Slide 16 Lab Information-pH titration Slide 17 Acid (or base) strength depends on the equilibrium constant Slide 18 Slide 19 pH Measurements are used to determine acid strength (K a ) A 0.10M solution of oxalic acid has a pH of 1.48. What is the K a value for oxalic acid? Slide 20 What is the value of K a for an acid, HA, for which a 0.240 M solution has a pH of 3.28? Is this acid stronger or weaker than oxalic acid? (K a =0.016) Slide 21 Determining K b from pH data A 0.300 M solution of a weak base has a pH of 9.20. What is K b ? Slide 22 Have a great weekend!