1)The half-cell, Tl | Tl+(1 mol L?1), is connected to a Pt | H+ | H2(1 atm) half

Question

1)The half-cell, Tl | Tl+(1 mol L?1), is connected to a Pt | H+ | H2(1 atm) half-cell in which the concentration of H+ is unknown. The measured cell voltage is 0.0841 V and the Pt | H2 | H+ half-cell is the cathode. Standard reduction potentials are given on the next page. (1A) Draw a diagram of the electrochemical cell, labeling all electrodes and solutions. (1B) (5 marks) What is the pH in the Pt | H+ | H2 half-cell? (1C) (3 marks) What is the value of the equilibrium constant for the reaction occurring in this cell?

Explanation / Answer

- Pt(s) | Mn2+(aq, 1 M), MnO4–(aq, 1 M) || Au3+(aq, 1 M) | Au(s) + MnO4 (-) /Mn(2+) couple is considered acid . . . MnO4 (-) /Mn(2+) . . . : .MnO4(-) + 8 H(+) + 5 e(-) = Mn(2+) + 4 H2O . . ] x 3 Au(3+) / Au(s) . . . . . . .: . . . . . . . . . . . . . . . . . . .Au . .= . .Au(3+) + 3 e(-) . .] x 5 . . . . . . . . . . . . . . . . . . . ¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯ . . . . . . . . . . . . . . . . . . . 3 MnO4(-) + 24 H(+) + 5 Ni = 3 Mn(2+) + 12 H2O + 5 Au(3+) K = [Mn(2+)]^3 x [Au(3+)]^5 / ( [MnO4(-)]^3 x [H(+)] ) [MnO4(-)] and [H(+)] decrease [Mn(2+)] and [Au(3+)] increase . . . therefore K tends to zero http://wc.pima.edu/~skolchens/C152OL/Ch21/Electro1.htm

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