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Chapter 18: Problem 17

Which species in each pair is a better oxidizing agent under standard-state conditions: (a) \(\mathrm{Br}_{2}\) or \(\mathrm{Au}^{3+} ?\) (b) \(\mathrm{H}_{2}\) or \(\mathrm{Ag}^{+} ?\) (c) \(\mathrm{Cd}^{2+}\) or \(\mathrm{Cr}^{3+} ?\) (d) \(\mathrm{O}_{2}\) in acidic media or \(\mathrm{O}_{2}\) in basic media?

Short Answer

Expert verified
The better oxidizing agents are \( \mathrm{Au}^{3+} \), \( \mathrm{Ag}^{+} \), \( \mathrm{Cd}^{2+} \), and \( \mathrm{O}_{2} \) in acidic media.

Step by step solution

01

Find the reduction potential for each species in pair (a)

Look up the reduction potentials in a standard reduction potential table. The standard reduction potential for \( \mathrm{Br}_{2} \) (Br2 + 2e- --> 2Br-) is +1.065V and for \( \mathrm{Au}^{3+} \) (Au3+ + 3e- --> Au) is +1.498V.
02

Compare the potentials for pair (a)

\( \mathrm{Au}^{3+} \) has the higher reduction potential. Therefore, it is a stronger oxidizing agent than \( \mathrm{Br}_{2} \).
03

Retrace steps 1 and 2 for pair (b)

The reduction potentials for \( \mathrm{H}_{2} \) (2H+ + 2e- --> H2) and \( \mathrm{Ag}^{+} \) (Ag+ + e- --> Ag) are 0V and +0.7996V respectively. Hence, \( \mathrm{Ag}^{+} \) is the stronger oxidizing agent.
04

Retrace steps 1 and 2 for pair (c)

The reduction potentials for \( \mathrm{Cd}^{2+} \) (Cd2+ + 2e- --> Cd) and \( \mathrm{Cr}^{3+} \) (Cr3+ + 3e- --> Cr) are -0.403V and -0.744V respectively. Therefore, \( \mathrm{Cd}^{2+} \) is the stronger oxidizing agent.
05

Retrace steps 1 and 2 for pair (d)

The reduction potentials for \( \mathrm{O}_{2} \) in acidic media (O2 + 4H+ + 4e- --> 2H2O) and \( \mathrm{O}_{2} \) in basic media (O2 + 2H2O + 4e- --> 4OH-) are +1.23V and +0.401V respectively. Thus, \( \mathrm{O}_{2} \) in acidic media is the stronger oxidizing agent.

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Most popular questions from this chapter

Calculate the pressure of \(\mathrm{H}_{2}\) (in atm) required to maintain equilibrium with respect to the following reaction at \(25^{\circ} \mathrm{C}\) : $$ \mathrm{Pb}(s)+2 \mathrm{H}^{+}(a q) \rightleftharpoons \mathrm{Pb}^{2+}(a q)+\mathrm{H}_{2}(g) $$ Given that \(\left[\mathrm{Pb}^{2+}\right]=0.035 M\) and the solution is buffered at \(\mathrm{pH} 1.60\).

Which of the following reagents can oxidize \(\mathrm{H}_{2} \mathrm{O}\) to \(\mathrm{O}_{2}(g)\) under standard-state conditions: \(\mathrm{H}^{+}(a q), \mathrm{Cl}^{-}(a q)\) \(\mathrm{Cl}_{2}(g), \mathrm{Cu}^{2+}(a q), \mathrm{Pb}^{2+}(a q), \mathrm{MnO}_{4}^{-}(a q)\) (in acid)?

Consider two electrolytic cells A and B. Cell A contains a \(0.20 \mathrm{M} \mathrm{CoSO}_{4}\) solution and platinum electrodes. Cell B differs from cell A only in that cobalt metals are used as electrodes. In each case, a current of \(0.20 \mathrm{~A}\) is passed through the cell for \(1.0 \mathrm{~h}\). (a) Write equations for the half-cell and overall cell reactions for these cells. (b) Calculate the products formed (in grams) at the anode and cathode in each case.

In the electrolysis of an aqueous AgNO \(_{3}\) solution, \(0.67 \mathrm{~g}\) of \(\mathrm{Ag}\) is deposited after a certain period of time. (a) Write the half- reaction for the reduction of \(\mathrm{Ag}^{+} .\) (b) What is the probable oxidation halfreaction? (c) Calculate the quantity of electricity used, in coulombs.

To remove the tarnish \(\left(\mathrm{Ag}_{2} \mathrm{~S}\right)\) on a silver spoon, a student carried out the following steps. First, she placed the spoon in a large pan filled with water so the spoon was totally immersed. Next, she added a few tablespoonful of baking soda (sodium bicarbonate , which readily dissolved. Finally, she placed some aluminum foil at the bottom of the pan in contact with the spoon and then heated the solution to about \(80^{\circ} \mathrm{C}\). After a few minutes, the spoon was removed and rinsed with cold water. The tarnish was gone and the spoon regained its original shiny appearance. (a) Describe with equations the electrochemical basis for the procedure. (b) Adding \(\mathrm{NaCl}\) instead of \(\mathrm{NaHCO}_{3}\) would also work because both compounds are strong electrolytes. What is the added advantage of using \(\mathrm{NaHCO}_{3} ?\) (Hint: Consider the \(\mathrm{pH}\) of the solution. \()\) (c) What is the purpose of heating the solution? (d) Some commercial tarnish removers contain a fluid (or paste) that is a dilute \(\mathrm{HCl}\) solution. Rubbing the spoon with the fluid will also remove the tarnish. Name two disadvantages of using this procedure compared to the one described above.
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