Chapter 7 Electrochemistry 87.2 Conductivity and its application Out-class extensive reading Levine: pp. 506-515 16.5 electric conductivity 16.6 Electrical conductivity of electrolyte solutions
Chapter 7 Electrochemistry §7.2 Conductivity and its application Out-class extensive reading: Levine: pp. 506-515, 16.5 electric conductivity 16.6 Electrical conductivity of electrolyte solutions
87.2 Conductivity and its application Key problems How can we evaluate the ability of an electrolytic solution to conduct electricity?
Key problems: How can we evaluate the ability of an electrolytic solution to conduct electricity? §7.2 Conductivity and its application
87.2 Conductivity and its application 1. Some concepts For metals: I For electrolyte solution: Ohm’sLaw U R: resistance. electric conductance(G): R Definition: G= I/R I Unit: Ohm, Q2 Unit: Q-I. mho. Siemens. S o: resistivity Reciprocal of resistance R A Unit: Q2-m conductivity(x: nition:K=l/p Unit: m
1. Some concepts For metals: I U R = R: resistance, Unit: Ohm, A l R = : resistivity Unit: ·m Ohm’s Law For electrolyte solution: Reciprocal of resistance electric conductance (G) : Definition: G = 1/R Unit: -1 , mho, Siemens, S conductivity () : Definition: = 1/ Unit: S·m-1 §7.2 Conductivity and its application
87.2 Conductivity and its application 2. Measurement of conductance: Conductance cell and conductance electrode R R R conductance cell Wheatstone Bridge Circuit A G=K conductance electrode
l A G = ~ G A C B D R2 R1 R4 R3 I Wheatstone Bridge Circuit §7.2 Conductivity and its application conductance cell Conductance cell and conductance electrode conductance electrode 2. Measurement of conductance:
87.2 Conductivity and its application 2. Measurement of conductance: a capacitor High-frequency alternative current, ca. D 1000 Hertz R R R 4 R 电导环 RR R3×R2=R4RF4 □ca G=K R Conductometer
R3 R2 = R4 R1 4 2 3 1 R R R R = 1 1 R G = 2. Measurement of conductance: ~ G A C B D F R2 R1 R4 R3 I R2 l A G = High-frequency alternative current, ca. 1000 Hertz ? Conductometer a capacitor! §7.2 Conductivity and its application
87.2 Conductivity and its application 2. Measurement of conductance K G KR=K R SS R K.三 K Cell constant R Calibration: The conductance cell is usually calibrated using standard aqueous kcl (potassium chloride)solution c/ moldm 0.001 0000.100 1.00 -1 0 0.0147 0.1411 1289 EXAMPLE The conductance of a cell containing an aqueous 0.0560 mol dm-3 KCI solution whose conductivity is 0. 753 Q2 -1. m-l is 0.0239 Q2-I When the same cell is filled with an aqueous 0.0836 mol dm-3 Nacl solution, its conductance is 0.0285 Q2- Calculate the conductivity of the Nacl solution
K G A l G = cell = s Rs = x Rx Calibration: The conductance cell is usually calibrated using standard aqueous KCl (potassium chloride ) solution. / S m 0 0.0147 0.1411 1.289 11.2 -1 c/ mol·dm 0 0.001 0.0100 0.100 1.00 -3 s x s x R R = Cell constant EXAMPLE The conductance of a cell containing an aqueous 0.0560 mol·dm-3 KCl solution whose conductivity is 0.753 -1·m-1 is 0.0239 -1 . When the same cell is filled with an aqueous 0.0836 mol·dm-3 NaCl solution, its conductance is 0.0285 -1 . Calculate the conductivity of the NaCl solution. 2. Measurement of conductance: §7.2 Conductivity and its application
87.2 Conductivity and its application 3. Influential factors of conductivity (1)Temperature 1. What can we learn from this tal fact 1 M 8 2. Why do we do electrolysis and electroplating using warm 日 electrolyte? 0.1N 05 01M 00 15 T/C
(1) Temperature 1.What can we learn from this experimental fact? 2. Why do we do electrolysis and electroplating using warm electrolyte? ice 3. Influential factors of conductivity §7.2 Conductivity and its application
87.2 Conductivity and its application 3. Influential factors of conductivity (2)Concentration 80 What can we learn from this figure? Can you give explanation to these HySON experimental facts? 60 (1)c KoH (2)maximum 40 Lic 20 MgSO4 HAc /mol.dr
(2) Concentration H2SO4 KOH LiCl MgSO4 HAc 5 10 15 c/mol·dm-3 0 10 20 30 40 50 60 70 80 /S·m - 1 What can we learn from this figure? Can you give explanation to these experimental facts? (1) c (2) maximum; (3) kinds 3. Influential factors of conductivity §7.2 Conductivity and its application
87.2 Conductivity and its application 4. Molar conductivity K∝C K=/C K Definition C why do we introduce the concept of 10 molar conductivity? c/moldm-3
4. Molar conductivity H2SO4 5 10 15 c/mol·dm-3 0 10 20 30 40 50 60 70 80 Definition Why do we introduce the concept of molar conductivity? c m c = m = c §7.2 Conductivity and its application /S·m - 1 §7.2 Conductivity and its application
87.2 Conductivity and its application 4. Molar conductivity (2)Concentration-dependence of molar conductivity ZEITSCHRIFT FUR ELEKTROCHEMIE Z f. Elektroch Bd. 13 CBER IONENBEWEGLICHKEITEN IM WASSER Ne, to, S, BI dieser Zeitschrift Begrime Aequivalentleitvermogea Jahren entstammenden Arbeiten von Folge des damal eeL verdannter sturen therten Bild! der relativ ere zunachst richtigen Werte ab und nicht einmal einheitlich behandeln, sondern die won Herrn Drucker far loner gesondert betrachtet. o, oooI n. abgeleitete Zahl 313, die Bei dem zweiten Versuch lagen far ver Friedrich Kohlrausch
(2) Concentration-dependence of molar conductivity 4. Molar conductivity Friedrich Kohlrausch §7.2 Conductivity and its application
