Question

Page 3 An electrochemical is prepared from a chromium metal electrode in contact solution of 0.500 M chromium (III) nitrate and a standard hydrogen half-cell elect The two half cells are connected by a porous disk or a KCl salt bridge. Standard Reduction Potentials at 298 K Cr+ (aq) + 3e ----> Cr(s) Cr+ (aq) + e ----> Cr2+ (aq) E° = -0.740 V E° = -0.440 V a) Write the reaction for the cell and calculate the standard free energy change. b) Sketch a diagram of this cell and completely label all of the parts. Where does oxidation and reduction occur in the cell? c) Using the data above, calculate the equilibrium constant for the spontaneous reaction at 298 K d) Describe how to calculate the equilibrium constant for the reaction, if the temperature is lowered to 198 K. Use information from Problem #2. The chromium half-cell is now connected to a hydrogen half-cell that contains a hydrogen gas pressure of 1.000 atm and only a weak acid, HA, at an initial concentration of 0.0500 M. Calculate the observed potential of this "new" cell, given the pK, of the weak acid is 7.15.

Answer 1

3t 2+ a) Reaction :- Coro cag) + 36 Crus) = -0.740 v. Co cag) té - Cretag E = -0.440 v. cell reaction - oxidation half: - Cris) rag) + 3é Reduction nach: - (Ces tag) te shtcaq)) x3. overall &- caes) + 363 3 302t. a cres) +2043 2042+ Full & Ecathode - Eanode 2 -0.440-(-0.740) 20.300v. s4=– nfeel 12 – 3 x 96500X0.3. 2-86850 I molt su 2-86.850 k 5 molt o r. no. of e exchange

Voltmeter crt metal electrode. T! ! ! 11 T! Tii! ! Grat Cr3+ Oxidation hall C++36- Salt Bridge containing kel Reduction half. (43+ fe Co27 Ch C). The si is negative i.c. – 26.850 kJ mott. The reaction is spontaneous. ou a – 2.303 ART log keq. - 86.850 – 2.303 x 3 x 8.314 x 298 x log keq. XV. - 86.850 -20303 x3 x 8.14x225 a log key. 860850 -0.00518 a log keq 16759,29948 Keae antilog (0.00518) 21.02 210012