Announcements. Shane s office hours will be in NS or 2120

Transcription

1 Announcements Lecture/Discussion information: Shane s office hours will be in NS or 2120 Quiz This Friday/Saturday at midnight (May 2/3) Due by 9 am on Monday, 5/5 Up through all of spectroscopy (Week 3) The only humans you can consult are your classmates Course website

2 Spectrophotometric Determination of pka The amount of each species can be quantified by visible spectroscopy Increasing ph Increasing ph Isosbestic point ensures we are only dealing with two species (In and HIn) Thanks, David! Determine pka of acetic acid and bromothymol blue Henderson Hasselbalch equation

3 [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 ) (1) A λ1 = ε (HIn,λ1) * b * [HIn] (2) A λ2 = ε _ (In,λ2) * b * [In ] λ1= HIn absorbs strongly, not In ; λ2= In absorbs strongly, not Hin λ1 λ2 (3) C T = [HIn] + [In ] (4) Low ph: A λ1, acidic = ε (HIn,λ1) * b * C T (5) High ph: A λ2, basic = ε _ (In,λ2) * b * C T Taking a ratio of (1) to (4) and (2) to (5): (6) A λ1 / A λ1, acidic = [HIn]/ C T (7) A λ2 / A λ2, basic = [In ]/ C T Thanks, David! Henderson Hasselbalch: (7) Divided by (6) [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 )

4 [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 ) (1) A λ1 = ε (HIn,λ1) * b * [HIn] (2) A λ2 = ε (In _,λ2) * b * [In ] λ1= HIn ONLY absorbs, not In ; λ2= In ONLY absorbs, not Hin λ1 λ2 (3) C T = [HIn] + [In ] (4) Low ph: A λ1, acidic = ε (HIn,λ1) * b * C T (5) High ph: A λ2, basic = ε (In _,λ2) * b * C T Taking a ratio of (1) to (4) and (2) to (5): (6) A λ1 / A λ1, acidic = [HIn]/ C T (7) A λ2 / A λ2, basic = [In ]/ C T Henderson Hasselbalch: (7) Divided by (6) [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 )

5 [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 ) (1) A λ1 = ε (HIn,λ1) * b * [HIn] (2) A λ2 = ε (In _,λ2) * b * [In ] λ1= HIn ONLY absorbs, not In ; λ2= In ONLY absorbs, not Hin λ1 λ2 (3) C T = [HIn] + [In ] Maximum absorbances (4) Low ph: A λ1, acidic = ε (HIn,λ1) * b * C T (5) High ph: A λ2, basic = ε (In _,λ2) * b * C T Taking a ratio of (1) to (4) and (2) to (5): (6) A λ1 / A λ1, acidic = [HIn]/ C T (7) A λ2 / A λ2, basic = [In ]/ C T Henderson Hasselbalch: (7) Divided by (6) [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 )

6 [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 ) (1) A λ1 = ε (HIn,λ1) * b * [HIn] (2) A λ2 = ε (In _,λ2) * b * [In ] λ1= HIn ONLY absorbs, not In ; λ2= In ONLY absorbs, not Hin λ1 λ2 (3) C T = [HIn] + [In ] Maximum absorbances (4) Low ph: A λ1, acidic = ε (HIn,λ1) * b * C T (5) High ph: A λ2, basic = ε (In _,λ2) * b * C T Taking a ratio of (1) to (4) and (2) to (5): (6) A λ1 / A λ1, acidic = [HIn]/ C T (7) A λ2 / A λ2, basic = [In ]/ C T Normalization, so that this value ranges from 0 to 1, is desired but does not occur when there is competing absorption! Henderson Hasselbalch: (7) Divided by (6) [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 )

7 [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 ) (1) A λ1 = ε (HIn,λ1) * b * [HIn] (2) A λ2 = ε (In _,λ2) * b * [In ] λ1= HIn ONLY absorbs, not In ; λ2= In ONLY absorbs, not Hin λ1 λ2 better λ2 (3) C T = [HIn] + [In ] Maximum absorbances (4) Low ph: A λ1, acidic = ε (HIn,λ1) * b * C T (5) High ph: A λ2, basic = ε (In _,λ2) * b * C T Taking a ratio of (1) to (4) and (2) to (5): (6) A λ1 / A λ1, acidic = [HIn]/ C T (7) A λ2 / A λ2, basic = [In ]/ C T better λ1 Normalization, so that this value ranges from 0 to 1, is desired but does not occur when there is competing absorption! Henderson Hasselbalch: (7) Divided by (6) [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 )

8 [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 ) (1) A λ1 = ε (HIn,λ1) * b * [HIn] (2) A λ2 = ε _ (In,λ2) * b * [In ] λ1= HIn absorbs strongly, not In ; λ2= In absorbs strongly, not Hin λ1 λ2 (3) C T = [HIn] + [In ] (4) Low ph: A λ1, acidic = ε (HIn,λ1) *b*c T = A λ1, max (5) High ph: A λ2, basic = ε _ (In,λ2) *b*c T = A λ2, max Taking a ratio of (1) to (4) and (2) to (5): (6) A λ1 / A λ1, acidic = [HIn]/ C T (7) A λ2 / A λ2, basic = [In ]/ C T Henderson Hasselbalch: (7) Divided by (6) [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 )

9 [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 ) (1) A λ1 = ε (HIn,λ1) * b * [HIn] (2) A λ2 = ε _ (In,λ2) * b * [In ] λ1= HIn absorbs strongly, not In ; λ2= In absorbs strongly, not Hin λ1 λ2 (3) C T = [HIn] + [In ] (4) Low ph: A λ1, acidic = ε (HIn,λ1) *b*c T = A λ1, max ; A λ2, acidic = ε (HIn,λ2) *b*c T = A λ2, min (5) High ph: A λ2, basic = ε (In _,λ2) *b*c T = A λ2, max ; A λ1, basic = ε (In _,λ1) *b*c T = A λ1, min Taking a ratio of (1) to (4) and (2) to (5): (6) A λ1 / A λ1, acidic = [HIn]/ C T (7) A λ2 / A λ2, basic = [In ]/ C T Henderson Hasselbalch: (7) Divided by (6) [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 )

10 [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 ) (1) A λ1 = ε (HIn,λ1) * b * [HIn] (2) A λ2 = ε _ (In,λ2) * b * [In ] λ1= HIn absorbs strongly, not In ; λ2= In absorbs strongly, not Hin λ1 λ2 (3) C T = [HIn] + [In ] (4) Low ph: A λ1, acidic = ε (HIn,λ1) *b*c T = A λ1, max ; A λ2, acidic = ε (HIn,λ2) *b*c T = A λ2, min (5) High ph: A λ2, basic = ε (In _,λ2) *b*c T = A λ2, max ; A λ1, basic = ε (In _,λ1) *b*c T = A λ1, min Normalizing the two values (from 0 to 1): (6) A λ1 / A λ1, acidic = [HIn]/ C T (7) A λ2 / A λ2, basic = [In ]/ C T Henderson Hasselbalch: (7) Divided by (6) [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 )

11 [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 ) (1) A λ1 = ε (HIn,λ1) * b * [HIn] (2) A λ2 = ε _ (In,λ2) * b * [In ] λ1= HIn absorbs strongly, not In ; λ2= In absorbs strongly, not Hin λ1 λ2 (3) C T = [HIn] + [In ] (4) Low ph: A λ1, acidic = ε (HIn,λ1) *b*c T = A λ1, max ; A λ2, acidic = ε (HIn,λ2) *b*c T = A λ2, min (5) High ph: A λ2, basic = ε (In _,λ2) *b*c T = A λ2, max ; A λ1, basic = ε (In _,λ1) *b*c T = A λ1, min Normalizing the two values (from 0 to 1): (6) (A λ1 A λ1, min ) / (A λ1, acidic/max A λ1, min ) = [HIn]/ C T (7) A λ2 / A λ2, basic = [In ]/ C T Henderson Hasselbalch: (7) Divided by (6) [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 )

12 [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 ) (1) A λ1 = ε (HIn,λ1) * b * [HIn] (2) A λ2 = ε _ (In,λ2) * b * [In ] λ1= HIn absorbs strongly, not In ; λ2= In absorbs strongly, not Hin λ1 λ2 (3) C T = [HIn] + [In ] (4) Low ph: A λ1, acidic = ε (HIn,λ1) *b*c T = A λ1, max ; A λ2, acidic = ε (HIn,λ2) *b*c T = A λ2, min (5) High ph: A λ2, basic = ε (In _,λ2) *b*c T = A λ2, max ; A λ1, basic = ε (In _,λ1) *b*c T = A λ1, min Normalizing the two values (from 0 to 1): (6) (A λ1 A λ1, min ) / (A λ1, acidic/max A λ1, min ) = [HIn]/ C T (7) (A λ2 A λ2, min ) / (A λ2, basic/max A λ2, min ) = [In ]/ C T Henderson Hasselbalch: (7) Divided by (6) [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 )

13 [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 ) (1) A λ1 = ε (HIn,λ1) * b * [HIn] (2) A λ2 = ε _ (In,λ2) * b * [In ] λ1= HIn absorbs strongly, not In ; λ2= In absorbs strongly, not Hin λ1 λ2 (3) C T = [HIn] + [In ] (4) Low ph: A λ1, acidic = ε (HIn,λ1) *b*c T = A λ1, max ; A λ2, acidic = ε (HIn,λ2) *b*c T = A λ2, min (5) High ph: A λ2, basic = ε (In _,λ2) *b*c T = A λ2, max ; A λ1, basic = ε (In _,λ1) *b*c T = A λ1, min Normalizing the two values (from 0 to 1): (6) (A λ1 A λ1, min ) / (A λ1, acidic/max A λ1, min ) = [HIn]/ C T (7) (A λ2 A λ2, min ) / (A λ2, basic/max A λ2, min ) = [In ]/ C T Henderson Hasselbalch: (7) Divided by (6) is uglier, but if you do it, your answers will be accurate!

14 Spectrophotometric Determination of pka The amount of each species can be quantified by visible spectroscopy Increasing ph Increasing ph Isosbestic point ensures we are only dealing with two species (In and HIn) Thanks, David! Determine pka of acetic acid and bromothymol blue Henderson Hasselbalch equation

15 Spectrophotometric Determination of pka The amount of each species can be quantified by visible spectroscopy Increasing ph Increasing ph Isosbestic point MOST LIKLEY we are only dealing with two species (In and HIn)

16 Spectrophotometric Determination of pka The amount of each species can be quantified by visible spectroscopy Increasing ph Increasing ph Isosbestic point MOST LIKLEY we are only dealing with two species (In and HIn) What is the definition of an isosbestic point?

17 Spectrophotometric Determination of pka The amount of each species can be quantified by visible spectroscopy Increasing ph Increasing ph Isosbestic point MOST LIKLEY we are only dealing with two species (In and HIn) What is the definition of an isosbestic point? Absorbance is constant regardless of [HIn] and [In ]

18 Spectrophotometric Determination of pka The amount of each species can be quantified by visible spectroscopy Increasing ph Increasing ph Isosbestic point MOST LIKLEY we are only dealing with two species (In and HIn) Mathematically, Abs isos = Const = A HIn + A In _ What is the definition of an isosbestic point? Absorbance is constant regardless of [HIn] and [In ]

19 Spectrophotometric Determination of pka The amount of each species can be quantified by visible spectroscopy Increasing ph Increasing ph Isosbestic point MOST LIKLEY we are only dealing with two species (In and HIn) Mathematically, Huh? Abs isos = Const =A HIn + A In _ = (ε (HIn,λisos) b[hin]) + (ε (In _,λisos) b[in ]) What is the definition of an isosbestic point? Absorbance is constant regardless of [HIn] and [In ]

20 Spectrophotometric Determination of pka The amount of each species can be quantified by visible spectroscopy Increasing ph Increasing ph Isosbestic point MOST LIKLEY we are only dealing with two species (In and HIn) Mathematically, Abs isos = Const =A HIn + A In _ = (ε (HIn,λisos) b[hin]) + (ε (In _,λisos) b[in ]) = (ε (λisos) b) x ([HIn] + [In ]) What is the definition of an isosbestic point? Absorbance is constant regardless of [HIn] and [In ]

21 Spectrophotometric Determination of pka The amount of each species can be quantified by visible spectroscopy Increasing ph Increasing ph Isosbestic point MOST LIKLEY we are only dealing with two species (In and HIn) Mathematically, Abs isos = Const =A HIn + A In _ = (ε (HIn,λisos) b[hin]) + (ε (In _,λisos) b[in ]) = (ε (λisos) b) x ([HIn] + [In ]) = ε (λisos) bc T What is the definition of an isosbestic point? Absorbance is constant regardless of [HIn] and [In ]

22 Spectrophotometric Determination of pka The amount of each species can be quantified by visible spectroscopy Increasing ph Increasing ph Isosbestic point MOST LIKLEY we are only dealing with two species (In and HIn) ε Mathematically, (HIn,λisos) = ε _ (In,λisos) Abs isos = Const =A HIn + A _ In = (ε (HIn,λisos) b[hin]) + (ε _ (In,λisos) b[in ]) = (ε (λisos) b) x ([HIn] + [In ]) = ε (λisos) bc T What is the definition of an isosbestic point? Absorbance is constant regardless of [HIn] and [In ]

23 Spectrophotometric Determination of pka The amount of each species can be quantified by visible spectroscopy Increasing ph Increasing ph Isosbestic point MOST LIKLEY we are only dealing with two species (In and HIn) ε (HIn,λisos) = ε (In _,λisos) We can have three, four, five, species if ε (S1,λisos) = ε (S2,λisos) = ε (S3,λisos) = ε (S4,λisos) = ε (S5,λisos) =

24 Final Note If you are struggling with Week 4 excel analysis/question 3 on problem set 4, remember: [In ]/[HIn] = (A λ1, acidic A λ2 )/(A λ2, basic A λ1 ) Thanks, David!

25 Final Note If you are struggling with Week 4 excel analysis/question 3 on problem set 4, remember: [In ]/[HIn] (A λ1, acidic A λ2 )/(A λ2, basic A λ1 )

26 Flashback: ICE Tables

27 Flashback: ICE Tables

28 Flashback: ICE Tables

29 Flashback: ICE Tables

30 RECALL: Weak acid salts will equilibrate

31 RECALL: Weak acid salts will equilibrate

32 RECALL: Weak acid salts will equilibrate

33 Real world buffers on a HUGE scale! CO 2 + H 2 O H 2 CO 3 H 2 CO 3 HCO 3 + H + pk a obs = 6.0 HCO 3 CO H + pk a obs = 9.1 Carbonates in the Ocean Historically, 1 the oceans have had ph = 8.179, which 0.9 is 6.6 nm H Today, the oceans are at ph = H2A 0.5 HA- This is a 31.7% increase in [H 2 CO 3 ] resulting in a 28.8% increase in [H + A2-0.4 Exp Values 0.3 ] and a 20.6% decrease in [CO ], which by Le Chatelier s Principle means 0.1 more CaCO 0 3 solublizes Alpha Alpha Fraction Plot for ph

34 Real world buffers on a HUGE scale! CO 2 + H 2 O H 2 CO 3 H 2 CO 3 HCO 3 + H + pk a obs = 6.0 HCO 3 CO H + pk a obs = 9.1 Historically, the oceans have been at ph = 8.179, which is 6.6 nm H + Today, the oceans are at ph = This is a 31.7% increase in [H 2 CO 3 ], due to CO 2 equilibration, resulting in a 28.8% increase in [H 3 O + ] and a 20.6% decrease in [CO 3 2 ], which by Le Chatelier s Principle means more rather insoluble coral structures (CaCO 3 ) solublize = SAD

35 Real world buffers on a HUGE scale! CO 2 + H 2 O H 2 CO 3 H 2 CO 3 HCO 3 + H + pk a obs = 6.0 HCO 3 CO H + pk a obs = 9.1 Historically, the oceans have been at ph = 8.179, which is 6.6 nm H + Today, the oceans are at ph = This is a 31.7% increase in [H 2 CO 3 ], due to CO 2 equilibration, resulting in a 28.8% increase in [H 3 O + ] and a 20.6% decrease in [CO 2 3 ], which by Le Chatelier s Principle means more rather insoluble coral structures (CaCO 3 ) solublize = SAD

36 Real world buffers on a HUGE scale! CO 2 + H 2 O H 2 CO 3 H 2 CO 3 HCO 3 + H + pk a obs = 6.0 HCO 3 CO H + pk a obs = 9.1 Historically, the oceans have been at ph = 8.179, which is 6.6 nm H + Today, the oceans are at ph = This is a 31.7% increase in [H 2 CO 3 ], due to CO 2 equilibration, resulting in a 28.8% increase in [H 3 O + ] and a 20.6% decrease in [CO 3 2 ], which by Le Chatelier s Principle means more rather insoluble coral structures (CaCO 3 ) solublize = SAD

37 Real world buffers on a HUGE scale! CO 2 + H 2 O H 2 CO 3 H 2 CO 3 HCO 3 + H + pk a obs = 6.0 HCO 3 CO H + pk a obs = 9.1 Historically, the oceans have been at ph = 8.179, which is 6.6 nm H + Today, the oceans are at ph = This is a 31.7% increase in [H 2 CO 3 ], due to CO 2 equilibration, resulting in a 28.8% increase in [H 3 O + ] and a 20.6% decrease in [CO 3 2 ], which by Le Chatelier s Principle means more rather insoluble coral structures (CaCO 3 ) solublize = SAD

38 Real world buffers on a HUGE scale! CO 2 + H 2 O H 2 CO 3 H 2 CO 3 HCO 3 + H + pk a obs = 6.0 HCO 3 CO H + pk a obs = 9.1 Carbonates in the Ocean Historically, 1 the oceans have had ph = 8.179, which 0.9 is 6.6 nm H Today, the oceans are at ph = H2A 0.5 HA- This is a 31.7% increase in [H 2 CO 3 ] resulting in a 28.8% increase in [H + A2-0.4 Exp Values 0.3 ] and a 20.6% decrease in [CO ], which by Le Chatelier s Principle means 0.1 more CaCO 0 3 solublizes Alpha Alpha Fraction Plot for ph This is not a problem if,

39 Real world buffers on a HUGE scale! CO 2 + H 2 O H 2 CO 3 H 2 CO 3 HCO 3 + H + pk a obs = 6.0 HCO 3 CO H + pk a obs = 9.1 Carbonates in the Ocean Historically, 1 the oceans have had ph = 8.179, which 0.9 is 6.6 nm H Today, the oceans are at ph = H2A 0.5 HA- This is a 31.7% increase in [H 2 CO 3 ] resulting in a 28.8% increase in [H + A2-0.4 Exp Values 0.3 ] and a 20.6% decrease in [CO ], which by Le Chatelier s Principle means 0.1 more CaCO 0 3 solublizes Alpha Alpha Fraction Plot for ph This is not a problem if, pk a-obs = 8.1!

40 Week 5 Objectives By the end of the week, you will be able to: Use electrochemical terminology to explain the thermodynamics and kinetics of redox reactions Describe various types of electrochemical cells Measure the electric potential of various galvanic cells

41 International Union of Pure and Applied Chemistry (IUPAC), strikes again (Accepted) Nomenclature and Terminology Coulomb (in units of C = A s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant) Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e, H + ) (Electrode) (electric) potential (V; in units of V = J/C) is written as a reduction, versus (Electro)chemical potential (in units of J) Potential energy (in units of J) Galvanic cells produce power (W = A x V = C/s x J/C = J/s) by spontaneous redox reactions Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable Batteries have anodes and cathodes, but the name changes depending on if one is discharging (galvanic) or charging (electrolytic), and so the terminology of negative or positive electrodes is preferred ΔG = nfe cell (Sources:Course textbook, and

42 International Union of Pure and Applied Chemistry (IUPAC), strikes again (Accepted) Nomenclature and Terminology Coulomb (in units of C = A s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant) differentiate Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e, H + ) (Electrode) (electric) potential (V; in units of V = J/C) is written as a reduction, versus (Electro)chemical potential (in units of J) Potential energy (in units of J) Galvanic cells produce power (W = A x V = C/s x J/C = J/s) by spontaneous redox reactions Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable Batteries have anodes and cathodes, but the name changes depending on if one is discharging (galvanic) or charging (electrolytic), and so the terminology of negative or positive electrodes is preferred ΔG = nfe cell integrate (Sources:Course textbook, and

43 International Union of Pure and Applied Chemistry (IUPAC), strikes again (Accepted) Nomenclature and Terminology Coulomb (in units of C = A s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant) Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e, H + ) (Electrode) (electric) potential (V; in units of V = J/C) is written as a reduction, versus (Electro)chemical potential (in units of J); Potential energy (in units of J) V = IR (Ohm s law) Galvanic cells produce power (W = A x V = C/s x J/C = J/s) by spontaneous redox reactions Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable Batteries have anodes and cathodes, but the name changes depending on if one is discharging (galvanic) or charging (electrolytic), and so the terminology of negative or positive electrodes is preferred ΔG = nfe cell (Sources:Course textbook, and

44 International Union of Pure and Applied Chemistry (IUPAC), strikes again (Accepted) Nomenclature and Terminology Coulomb (in units of C = A s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant) Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e, H + ) (Electrode) (electric) potential (V; in units of V = J/C) is written as a reduction, versus (Electro)chemical potential (in units of J); Potential energy (in units of J) V = IR (Ohm s law) Galvanic cells produce power (W = A x V = C/s x J/C = J/s) by spontaneous redox reactions Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable You can subtract redox potentials but do not change the Batteries have anodes and cathodes, but the name sign changes of the potential depending and on if then one is discharging (galvanic) or charging (electrolytic), call and it so an the oxidation terminology potential! of negative or positive electrodes is preferred ΔG = nfe cell E 0 (Cu 2+/0 ) = V vs. NHE E 0 (Cu 0/2+ ) = 0.34 V vs. NHE is incorrect! (Sources:Course textbook, and

45 International Union of Pure and Applied Chemistry (IUPAC), strikes again (Accepted) Nomenclature and Terminology Coulomb (in units of C = A s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant) Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e, H + ) (Electrode) (electric) potential (V; in units of V = J/C) is written as a reduction, versus (Electro)chemical potential (in units of J); Potential energy (in units of J) V = IR (Ohm s law) E 0 (Cu 2+/0 ) = V vs. NHE E 0 (Cu 0/2+ ) = 0.34 V vs. NHE Galvanic cells produce power (W = A x V = C/s x J/C = J/s) by spontaneous redox reactions Based on our current sign is incorrect! convention, Electrolytic itcells is require best toa power only input writeto drive redox reactions; thus, the reactions are thermodynamically unfavorable You can subtract redox reduction potentials; however, if we potentials but do not change the lived Batteries in an oxidation-potential-centric have anodes and cathodes, but the name sign changes of the potential depending and on if then one is world, discharging we could (galvanic) writeor them charging all(electrolytic), as call and it so an the oxidation terminology potential! of negative or oxidation positive potentials; electrodes is simply preferred put, it is best to not mix the conventions ΔG = nfe cell (Sources:Course textbook, and

46 International Union of Pure and Applied Chemistry (IUPAC), strikes again (Accepted) Nomenclature and Terminology Coulomb (in units of C = A s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant) Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e, H + ) (Electrode) (electric) potential (V; in units of V = J/C) is written as a reduction, versus (Electro)chemical potential (in units of J); Potential energy (in units of J) V = IR (Ohm s law) Galvanic cells produce power (W = A x V = C/s x J/C = J/s) by spontaneous redox reactions Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable Batteries have anodes and cathodes, but the name changes depending on if one is discharging (galvanic) or charging (electrolytic), and so the terminology of negative or positive electrodes is preferred ΔG = nfe cell (Sources:Course textbook, and

47 International Union of Pure and Applied Chemistry (IUPAC), strikes again (Accepted) Nomenclature and Terminology Coulomb (in units of C = A s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant) Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e, H + ) (Electrode) (electric) potential (V; in units of V = J/C) is written as a reduction, versus (Electro)chemical potential (in units of J); Potential energy (in units of J) V = IR (Ohm s law) Galvanic cells produce power (W = A x V = C/s x J/C = J/s) by spontaneous redox reactions Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable Batteries have anodes and cathodes, but the name changes depending on if one is discharging (galvanic) or charging (electrolytic), and so the terminology of negative or positive electrodes is preferred ΔG = nfe cell opposites (Sources:Course textbook, and

48 International Union of Pure and Applied Chemistry (IUPAC), strikes again (Accepted) Nomenclature and Terminology Coulomb (in units of C = A s) is the unit of charge (96,485 C are in a mole of singly charged species = Faraday constant) Electricity is the flow of current (A = C/s) and is negative (cathodic) or positive (anodic) depending on the direction and sign of the current-carrying species (e.g. e, H + ) (Electrode) (electric) potential (V; in units of V = J/C) is written as a reduction, versus (Electro)chemical potential (in units of J); Potential energy (in units of J) V = IR (Ohm s law) Galvanic cells produce power (W = A x V = C/s x J/C = J/s) by spontaneous redox reactions Electrolytic cells require a power input to drive redox reactions; thus, the reactions are thermodynamically unfavorable Batteries have anodes and cathodes, but the name changes depending on if it is being discharged (galvanic) or charged (electrolytic), and so the terminology of negative or positive electrode is preferred ΔG = nfe cell, and standard state is pure solvent/solid, 1 M solution, and 1 bar gases

49 Oxidation-Reduction Reactions Oxidation Reduction

50 reductant (reducing agent) oxidant (oxidizing agent)

51 Common Inert Electrodes: Platinum, Carbon, Gold Common Reactive Electrodes: Copper, Zinc, Cadmium, Lead, Silver high resistance to measure potential Pt Ce 3+ (aq), Ce 4+ (aq) Fe 3+ (aq), Fe 2+ (aq) Pt

52 high resistance to measure potential Pt Ce 3+ (aq), Ce 4+ (aq) Fe 3+ (aq), Fe 2+ (aq) Pt

53 ΔG < 0 is favorable high resistance to measure potential E cell > 0 is favorable Pt Ce 3+ (aq), Ce 4+ (aq) Fe 3+ (aq), Fe 2+ (aq) Pt

54 Nernst equation Reaction quotient as product and quotient of species activities high resistance to measure potential Walther Nernst ( ) from Wiki Pt Ce 3+ (aq), Ce 4+ (aq) Fe 3+ (aq), Fe 2+ (aq) Pt

55 Nernst equation Reaction quotient as product and quotient of species activities high resistance to measure potential Δ ln Thus, ln Pt Ce 3+ (aq), Ce 4+ (aq) Fe 3+ (aq), Fe 2+ (aq) Pt

56 Nernst equation Reaction quotient as product and quotient of species activities high resistance to measure potential Δ ln Thus, ln log 59.2 mv log (at 25 C) 59.2 mv is termed a Nernstian shift Pt Ce 3+ (aq), Ce 4+ (aq) Fe 3+ (aq), Fe 2+ (aq) Pt

57

58

59

60 standard (SHE)

61 standard (SHE) Thus, the potentials for half-cell reactions are actually full-cell electrical potential (difference)s against SHE!

62 standard (SHE) * Normal hydrogen electrode (NHE) is an empirical SHE ([H + ] = 1; not standard state) * Standard hydrogen electrode (SHE) is a hypothetical, perfect NHE (a = 1; not empirical) * Reversible hydrogen electrode (RHE) is the SHE but the same regardless of ph * And generally, formal potentials (E 0 ) take into consideration non idealities and changes in ionic strengths so that the reaction quotient only has concentrations, and not activities

63 standard (SHE) * Normal hydrogen electrode (NHE) is an empirical SHE ([H + ] = 1; not standard state) * Standard hydrogen electrode (SHE) is a hypothetical, perfect NHE (a = 1; not empirical) * Reversible hydrogen electrode (RHE) is the SHE but the same regardless of ph * And generally, formal potentials (E 0 ) take into consideration non idealities and changes in ionic strengths so that the reaction quotient only has concentrations, and not activities Potential Standard Potential

64 standard (SHE) Given E 0 = 0, what is this experimental redox potential versus? Potential Standard Potential

65 standard (SHE) Given E 0 = 0, what is this experimental redox potential versus? vs. SHE Potential Standard Potential

66 The Daniell Cell (1836) (liquid electrolyte primary galvanic cell) low resistance to measure current I cell John Frederic Daniell ( ) from Wiki Zn Cu Zn(s) Zn 2+ (aq) Cu 2+ (aq) Cu(s) Zn Zn 2+ (aq) Cu 2+ (aq) Cu

67 The Daniell Cell (1836) (liquid electrolyte primary galvanic cell) low resistance to measure current I cell This only works for a few seconds and then stops due to Kirchhoff s current law, which states that all current at each node must sum to zero. Zn Cu Zn(s) Zn 2+ (aq) Cu 2+ (aq) Cu(s) Zn Zn 2+ (aq) Cu 2+ (aq) Cu

68 The Daniell Cell (1836) (liquid electrolyte primary galvanic cell) low resistance to measure current I cell A + i B i Zn Cu Now it works! Salt bridge contains an inert, redox inactive salt solution (electrolyte) Zn(s) Zn 2+ (aq) Cu 2+ (aq) Cu(s) Zn Zn 2+ (aq) Cu 2+ (aq) Cu

69 The Daniell Cell (1836) (liquid electrolyte primary galvanic cell) low resistance to measure current I cell A i + Will eventually fully discharge and reach equilibrium (ΔG = 0) Then, either direction of polarization bias results in electrolytic function (charging) B i Zn Cu Zn(s) Zn 2+ (aq) Cu 2+ (aq) Cu(s) Zn Zn 2+ (aq) Cu 2+ (aq) Cu

70 The Daniell Cell (1836) (liquid electrolyte primary galvanic cell) * Name this cell type * Identify anode * Identify cathode * Name the electrode signs low resistance to measure current I cell A i + B i Zn Cu Zn(s) Zn 2+ (aq) Cu 2+ (aq) Cu(s) Zn Zn 2+ (aq) Cu 2+ (aq) Cu

71 = Ideally polarizable electrodes

72 can be

73 can be; but they are not. Use SHE!

74

75

76

77 MOST COMMON BATTERIES

78 MOST COMMON BATTERIES Separator is the salt bridge; it contains an inert, redox inactive salt solution (electrolyte)

79 MOST COMMON BATTERIES Separator is the salt bridge; it contains an inert, redox inactive salt solution (electrolyte)

80 MOST COMMON BATTERIES Button cell CATHODE CAP Separator is the salt bridge; it contains an inert, redox inactive salt solution (electrolyte)

81 MOST COMMON BATTERIES Button cell intercalated CATHODE CAP Separator is the salt bridge; it contains an inert, redox inactive salt solution (electrolyte)

82 MOST COMMON BATTERIES Button cell intercalated CATHODE CAP Separator is the salt bridge; it contains an inert, redox inactive salt solution (electrolyte) Dendrites = Shunts

83 ENERGY STORAGE from Joint Center for Energy Storage Research (JCESR) website (

84 ENERGY STORAGE Battery from Joint Center for Energy Storage Research (JCESR) website ( Redox flow battery

85 DISCUSSION TIME!

86 DISCUSSION TIME!

87 DISCUSSION TIME! You try! (a) What is the standard E cell for a galvanic cell based on zinc and silver? (b) If we were to electrolytically charge this cell, what potential bias would we have to apply?

88 DISCUSSION TIME! You try! (a) What is the standard E cell for a galvanic cell based on zinc and silver? (b) If we were to electrolytically charge this cell, what potential bias would we have to apply? (a) E cell = V ( 0.76 V) = 1.56 V (b) E bias < 1.56 V

89 DISCUSSION TIME! Latimer diagrams are useful for visualizing the redox series for an element (they are also useful when determining if disproportionation occurs) Oxidation 1,69 V Reduction from Wiki

90 DISCUSSION TIME! Latimer diagrams are useful for visualizing the redox series for an element (they are also useful when determining if disproportionation occurs) Oxidation 1,69 V Reduction from Wiki

91 DISCUSSION TIME! Latimer diagrams are useful for visualizing the redox series for an element (they are also useful when determining if disproportionation occurs) Oxidation 1,69 V Reduction Disproportionation spontaneous and simultaneous reduction and oxidation of a molecule from Wiki

92 DISCUSSION TIME! Latimer diagrams are useful for visualizing the redox series for an element (they are also useful when determining if disproportionation occurs) Oxidation 1,69 V Reduction Disproportionation spontaneous and simultaneous reduction and oxidation of a molecule (1) Does Mn 2+ disproportionate? (2) What is the standard reduction potential of MnO 4 to MnO 2? from Wiki

93 DISCUSSION TIME! Latimer diagrams are useful for visualizing the redox series for an element (they are also useful when determining if disproportionation occurs) Oxidation 1,69 V Reduction Disproportionation spontaneous and simultaneous reduction and oxidation of a molecule (1) Does Mn 2+ disproportionate? (2) What is the standard reduction potential of MnO 4 to MnO 2? Reduction: Mn 2+ Mn o E o = V Oxidation: Mn 2+ Mn 3+ E o = V from Wiki

94 DISCUSSION TIME! Latimer diagrams are useful for visualizing the redox series for an element (they are also useful when determining if disproportionation occurs) Oxidation 1,69 V Reduction Disproportionation spontaneous and simultaneous reduction and oxidation of a molecule (1) Does Mn 2+ disproportionate? NO. E o = = 0.33 V (2) What is the standard reduction potential of MnO 4 to MnO 2? Reduction: Mn 2+ Mn o E o = V Oxidation: Mn 2+ Mn 3+ E o = V from Wiki

95 DISCUSSION TIME! Latimer diagrams are useful for visualizing the redox series for an element (they are also useful when determining if disproportionation occurs) Oxidation 1,69 V Reduction Disproportionation spontaneous and simultaneous reduction and oxidation of a molecule (1) Does Mn 2+ disproportionate? NO. E o = = 0.33 V (2) What is the standard reduction potential of MnO 4 to MnO 2? ΔG o = nfe o = 3FE o from Wiki

96 DISCUSSION TIME! Latimer diagrams are useful for visualizing the redox series for an element (they are also useful when determining if disproportionation occurs) Oxidation 1,69 V Reduction Disproportionation spontaneous and simultaneous reduction and oxidation of a molecule (1) Does Mn 2+ disproportionate? NO. E o = = 0.33 V (2) What is the standard reduction potential of MnO 4 to MnO 2? ΔG o = nfe o = 3FE o ΔG o = nfe o 1 + nfe o 2 = F((1 x 0.56 V) + (2 x 2.26 V)) = F(5.08 V) from Wiki

97 DISCUSSION TIME! Latimer diagrams are useful for visualizing the redox series for an element (they are also useful when determining if disproportionation occurs) Oxidation 1,69 V Reduction Disproportionation spontaneous and simultaneous reduction and oxidation of a molecule from Wiki (1) Does Mn 2+ disproportionate? NO. E o = = 0.33 V (2) What is the standard reduction potential of MnO 4 to MnO 2? ΔG o = nfe o = 3FE o ΔG o = nfe o 1 + nfe o 2 = F((1 x 0.56 V) + (2 x 2.26 V)) = F(5.08 V) Set them equal to each other, and thus, 3E o = 5.08 and E o = 1.69 V

98 Week 5 Objectives By the end of the week, you will be able to: Use electrochemical terminology to explain the thermodynamics and kinetics of redox reactions Describe various types of electrochemical cells Measure the electric potential of various galvanic cells