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Chapter 17: Q5P (page 427)

(a) which voltage,V1orV2in the diagram is constant in controlled-potential electrolysis? Which are the working, auxiliary, and reference electrodes in the diagram?

(b) Explain how the Luggin capillary in Figure 17-4 measures the electric potential at the opening of the capillary.

Short Answer

Expert verified
  • The voltage V2in the diagram is constant in controlled – potential electrolysis.

Step by step solution

01

Definition of Controlled – potential electrolysis:

  • Bulk electrolysis is also known as potentiostatic coulometry or controlled potential coulometry.
  • The experiment is a form of coulometry which generally employs a three electrode system controlled by a potentiostat.
02

Illustration of electrodes: 

  • The electrodes are: Auxiliary, reference, working


03

 Measuring electric potential by using Luggin capillary: 

  • The potential of the electrode we are testing is measured so that along the surface of this electrode at a distance of 2-3 mm put the top of the so-called Luggin's capillary that is over the vessel and / or of the corresponding electrolyte bridges connected to some reference electrode with which forms a separate cell.
  • With the help of a known value of the reference electrode potential and of the measured cell voltage the electrode potential is calculated.
  • In Figure 17-4, the potentiometer measures the voltage between the Cu electrode and a reference electrode immersed in 1.0 V2and connected to the bulk solution via a Luggin capillary, AgCl.

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Most popular questions from this chapter

The Weston cell is a stable voltage standard formerly used in potentiometers. (The potentiometer compares an unknown voltage with that of the standard. In contrast with the conditions of this problem, very little current may be drawn from the cell if it is to be a voltage standard.)

How much work (J)can be done by the Weston cell if the voltage is 1.02 V and1.00mLof Hg(density = 13.52g/mL) is deposited?

(b) If the cell passes current through a100-Ω resistor that dissipates heat at a rate of0.209 J/min, how many grams of are oxidized each hour? (This question is not meant to be consistent with part (a). The voltage is no longer 1.02volts.)

Suppose that the diffusion current in a polarogram for reduction of Cd2+at a mercury electrode is14μAIf the solution containsof 25mLof0.50mMCd2+what percentage ofCd2+is reduced in the 3.4 min required to scan from-0.6to-1.2V?

Measuring the size of a microelectrode by cyclic voltammetry.

(a) Redox chemistry for ferrocyanide in Figure 17-32 was given at the beginning of Section 17-5. Write the analyte half-reaction that occurs at the upper plateau near 0.4 Vand at the lower plateau near 0 V(versus S.C.E.).

(b) The limiting current Ilimit, which is the difference between the upper and lower plateaus, is related to the radius of the disk-shaped electrode (r)and the diffusion coefficient (D)and bulk concentration (C)of the analyte:

Ilimit4nFDCr

Where nis the number of electrons in the half-reaction and F is the Faraday constant. In this equation, the units of concentration should be mol/m3to be consistent with the other quantities in SI units. The diffusion coefficient for ferrocyanide cited in the reference for Figure 17 - 32is 9.2×10-10m/sin water at25°C. Calculate the radius of the microelectrode.

A0.3268-gunknown containing Pb(CH3CHOHCO2)2(leadLactate, FM 385.3) plus inert material was electrolyzed to produce 0.1111gofPbO2(FM239.2). Was the PbO2deposited at the anode or at the cathode? Find the weight percent of lead lactate in theUnknown.

How many hours are required for 0.100 mol of electrons to flow through a circuit if the current is 1.00 A?
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