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Chapter 17: Q14P (page 428)

Explain how amperometric end-point detection in Figure17-9 operates.

Short Answer

Expert verified

$cathode B r_{2} + 2 e^{-} \to 2 B r^{-} a n o d e 2 B r^{-} \to B r_{2} + 2 e^{-}$

Step by step solution

01

Amperometric method:

End-point detection of complexometric titrations of metal ions in unbuffered solutions with disodium ethylenediaminetetraacetate is proposed as an amperometric technique $(Na 2 H 2 Y)$ . It is based on the employment of a platinum disc microelectrode as a sensor for detecting the hydrogen ions supplied during the titration.

02

Find amperometric end-point detection:

${Br}_{2}$ generated at the Pt anode reacts with cyclohexene. When cyclohexene is consumed, the concentration of increases, signaling the end of the reaction. The increase in ${Br}_{2}$ concentration is detected by measuring the current between the two detector electrodes:

cathode ; $B r_{2} + 2 e^{-} \to 2 B r^{-} a n o d e 2 B r^{-} \to B r_{2} + 2 e^{-}$

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Most popular questions from this chapter

${cd}^{2 +}$ was used as an internal standard in the analysis of ${Pb}^{2 +}$ by square wave polarography. ${Cd}^{2 +}$ gives a reduction wave at -0.60 V and ${Pb}^{2 +}$ gives a reduction wave at –0.40 V. It was first verified that the ratio of peak heights is proportional to the ratio of concentrations over the whole range employed in the experiment. Here are results for known and unknown mixtures:

The unknown mixture was prepared by mixing $25.00 (\pm 0.05) mL$ of unknown (containing only ${Pb}^{2 +}$ ) plus $10.00 (\pm 0.05) mL$ of $3.23 (\pm 0.01) \times 10^{- 4} {MCd}^{2 +}$ and diluting to $50.00 (\pm 0.05) mL$ .

(a) Disregarding uncertainties, find $[{Pb}^{2 +}]$ in the undiluted unknown.

(b) Find the absolute uncertainty for the answer to part (a).

Will(cathode) =0.19 Vreduce $0.10 M {SbO}^{+}$ at pH 2 by the reaction ${SbO}^{+} + 2 H^{+} + 3 e^{-} ⇌ Sb (s) + H_{2} O, E^{°} = 0.208 V$ ?

In $1 MN {NH}_{3} / 1 M {NH}_{4} CI$ solution, ${Cu}^{2 +}$ is reduced to ${Cu}^{+}$ near -0.3V(versus S.C.E.), and ${Cu}^{+}$ is reduced to $Cu (inHg)$ near 0.6V.

(a) Sketch a qualitative sampled current polarogram for a solution of ${Cu}^{+}$ .

(b) Sketch a polarogram for a solution of ${Cu}^{2 +}$ .

(c) Suppose that Pt, instead of Hg, were used as the working electrode. Which, if any, reduction potential would you expect to change?

The cyclic voltammogram of the antibiotic chloramphenicol (abbreviated) is shown here. The first cathodic scan goes from 0 to -1.0 V. The first cathodic wave, , is from the reaction ${RNO}_{2} + 4 e^{-} + 4 H^{+} \to RNHOH + H_{2} O$ . Peak B in the reverse anodic scan could be assigned to $RNHOH \to RNO + 2 H^{+} + 2 e^{-}$ . In the second cathodic scan from +0.9 to -0.4 V, the new peak C appears. Write a reaction for peak C and explain why peak C was not seen in the initial scan.

Cyclic voltammogram of 3.7 ×10^-4 chloramphenicol in 0.1 M acetate buffer, pH 4.62. The voltage of the carbon paste working electrode was scanned at a rate of 350 mV/s. [Data from P. T. Kissinger and W. R. Heineman, “Cyclic Voltammetry,” J. Chem. Ed. 1983, 60, 702.]

17-18. $H_{2} S (aq)$ can be analysed by titration with coulometric ally generated $l_{2} .$

role="math" localid="1654768790950" $H_{2} S + l_{2} \to S (s) + 2 H^{+} + 2 l^{-}$

To $50.00 mL$ of sample were added 4gof KI. Electrolysis required812s at. 52.6mA . Calculate the concentration ofrole="math" localid="1654769975824" $H_{2} S (μg / mL)$ in the sample.

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