475

25 Homework exercises. 1. Calculate the potential of a silver electrode (Ag + /Ag  0 ) immersed in a 0.01 MAgNO 3  solution at 25  0 C, φ  0 (Ag + /Ag  0 ) = +0.8 V. Answer : 0.68 V. 2. The potential of a zinc electrode placed in a solution of its own salt at T = 298 K wasφ (Zn  2+ /Zn  0 )=–0.819 V. Calculate the concentration of Zn  2+ ions ifφ  0 (Zn  2+ /Zn  0 ) = – 0.76 V. Answer : C (Zn  2+ ) = 0.01 mol/l. 3. Calculate the redox potential of the Sn  4+ /Sn  2+ system containing a mixture of SnCl 2  and SnCl 4  salts at 298 K, if C (Sn  2+ ) = 0.01 mole/l, C (Sn  4+ ) = 0.05 mol/l. φ 0 (Sn  4+ /Sn  2+ ) = 0.15 V. Answer : 0.17 V. 4. Calculate the standard oxidation-reduction potential (φ  0 (Fe  3+ /Fe  2+ ) at 298 K, if the E mf of the galvanic cell consisting of this redox electrode and a saturated silver chloride electrode is +0.55 V, C (Fe  2+ ) = 0.05 mol/l, C (Fe  3+ ) = 0.02 mol/l, the potential of saturated silver chloride electrode is φ sce = 0.201 V. Galvanic circuit: Ag, AgCl (т) | KCl (нас.) || Fe  2+ , Fe  3+ | Pt Answer : 0.77 V. 5. The potential of the hydrogen electrode immersed in the test solution is –0.118 Vat a temperature of 25  0 C. Calculate the pH of this solution. Answer : 2. 6. Calculate the potential of the hydrogen electrode immersed in a solution of NaOH at a concentration of 0.001 mol/l at 100 °C. Answer : –0.62 V. 7. The galvanic cell is made up of silver chloride and hydrogen elec- trodes immersed in gastric juice. The Emf of the element is 0.286 V, and the- potentialof silver chloride is 0.201Vat 370 С. Calculate the pH of gastric juice. Answer: 1.38 V. 8. A galvanic circuit was made of hydrogen and silver chloride electrodesto measure the pH of the bile from the bladder. The potential of saturated silver chloride electrode is φ sce = 0.201 V. The E mf measured at 25 °C was 0.577 V. Calculate the pH of the bile. Answer : 5.74. 9. The concentrations of MnO 4 – and Mn  2+ ions are equal to each other. Then 20% of Mn  2+ ions were oxidized. How will the redox potential of the MnO 4 – /Mn  2+ system change? The reaction proceeds at a constant pH value and a temperature of 25 °C. Answer : will increase by 0.002 V. Laboratory work: Determination of the molar concentration of the hydrogen peroxide equivalent by the permanganatometry method.