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Chapter 17: Q25P (page 429)

What is a Clark electrode, and how does it work?

Short Answer

Expert verified

The process of Clark electrode has to be explained.

Step by step solution

01

Define Clark electrode

The Clark electrode is an electrode that allows amper metric measurement of dissolved oxygen activity. The electrode has glass body with a 5-mm opening at the base. Inside this opening is a 10 to 10 to 40 - mm long plug of silicone rubber, which is permeable to $O_{2}$ . Oxygen diffuses into the electrode through the rubber and is reduced at the Au tip on the Pt wire, held at -0.75V with respect to the $A g |A g C|$ reference electrode. A Clark electrode is calibrated by placing it in solutions of known $O_{2}$ concentration, and a graph of current versus $[O O_{2}]$ .

02

Explain the process of clark electrode.

By reducing oxygen to water on platinum electrode at -0.75V voltage of with respect to silver-silver chloride.
Silicone rubber of size $10 μm to 40 μm$ to permeable to oxygen is filled on body of platinum electrode.
The concentration of oxygen is proportional to current. The electrode in known oxygen concentration should be calibrated.

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Most popular questions from this chapter

Coulometric titration of sulfite in wine. Sulfur dioxide is added to many foods as a preservative. In aqueous solution, the following species are in equilibrium:

Bisulfite reacts with aldehydes in food near neutral pH:

Sulfite is released from the adduct in 2MNaOH and can be analyzed by its reaction with $I_{3}^{-}$ to give $I^{-}$ and sulfate. Excess $I_{3}^{-}$ must be present for quantitative reaction.

Here is a coulometric procedure for analysis of total sulfite in white wine. Total sulfite means all species in Reaction and the adduct in Reaction . We use white wine so that we can see the color of a starch-iodine end point.

1. Mix 9.00 mL of wine plus 0.8gNaOH and dilute to 10.00mL. The releases sulfite from its organic adducts.

2. Generate $I_{3}^{-}$ at the working electrode (the anode) by passing a known current for a known time through the cell in Figure 17 - 10. The cell containsofacetate buffer () plus. In the cathode compartment, is reduced to $H_{2} + {OH}^{-}$ . The frit retards diffusion of into the main compartment, where it would react with $I_{3}^{-}$ to give ${IO}^{-}$ .

3. Generate $I_{3}^{-}$ at the anode with a current of for.

4. Inject 2.000mL of the wine/ solution into the cell, where the sulfite reacts with leaving excess.

5. Add of thiosulfate to consume by Reaction and leave excess thiosulfate.

6. Add starch indicator to the cell and generate fresh $I_{3}^{-}$ with a constant current of 10.0mA. A time of 131s was required to consume excess thiosulfate and reach the starch end point.

(a) In what pH range is each form of sulfurous acid predominant?

(b) Write balanced half-reactions for the anode and cathode.

(c) At pH 3.7, the dominant form of sulfurous acid isand the dominant form of sulfuric acid is ${HSO}_{4}^{2 -}$ . Write balanced reactions between andand between $I_{3}^{-}$ and ${HSO}_{3}^{-}$ thiosulfate.

(d) Find the concentration of total sulfite in undiluted wine.

17-16. The sensitivity of a coulometer is governed by the delivery of its minimum current for its minimum time. Suppose thatcan be delivered for 0. 1s.

(a) How many moles of electrons are delivered by 5mAfor 0. 1s ?

(b) How many millilitres of a 0.01 Msolution of a two-electron reducing agent is required to deliver the same number of electrons?

Suppose we wish to electrolyze $I^{-}$ to $I_{3}^{-}$ in a 0.10M Klsolution containing $3.0 \times 10^{- 5} M$ $I_{3}^{-}$ at pH 10.00with $P_{H_{2}} = 1.00 bar$ .

$3 I^{-} + 2 H_{2} O \to I_{3}^{-} + H_{2} (g) + 2 {OH}^{-}$

(a) Find the cell voltage if no current is flowing.

(b) Then suppose that electrolysis increases $[I_{3}^{-}]$ to $3.0 \times 10^{- 4} M$ , but other concentrations are unaffected. Suppose that the cell resistance is $2.0 Ω$ , the current is 63 mA, the cathode overpotential is 0.382V, and the anode overpotential is 0.025 V. What voltage is needed to drive the reaction?

Find the voltage in part (b) ifrole="math" localid="1663645169401" ${[I^{-}]}_{s} = 0.01 M$ .

The chlor-alkali process ⁵⁴in which seawater is electrolyzed to make CI₂ andNaOH, is the second most important commercial electrolysis, behindAIproduction.

Anode: ${CI}^{-} \to \frac{1}{2} {CI}_{2} + e^{-}$

HgCathode: ${Na}^{+} + H_{2} O + e^{-} \to NaOH + \frac{1}{2} H_{2}$

The Nafion membrane (page 421) used to separate the anode and cathode compartments resists chemical attack. Its anionic side chains permit conduction ofNa⁺ , but not anions. The cathode compartment contains pure water, and the anode compartment contains seawater from which Ca²⁺ and Mg²⁺ have been removed. Explain how the membrane allows NaOH to be formed free ofNaCI.

Consider the cyclic voltammogram of the ${Co}^{3 +}$ compoundrole="math" localid="1663646447735" $Co {(B_{9} C_{2} H_{11})}_{2}^{-}$ . Suggest a chemical reaction to account for each wave. Are the reactions reversible? How many electrons are involved in each step? Sketch the sampled current and square wave polarograms expected for this compound.

Cyclic voltammogramofrole="math" localid="1663646461802" $Co {(B_{9} C_{2} H_{11})}_{2}^{-}$ . [Data from W. E. Geiger, Jr., W. L. Bowden, and N. El Murr, "An Electrochemical Study of the Protonation Site of the Cobaltocene Anion and of Cyclopentadienylcobalt(I) Dicarbollides," Inorg. Chem. 1979,18,2358.]

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