Manganese may play an important role in chemical cycles in the oceans. Two reactions involving manganese (in acid solution) are the reduction of nitrate ions (to NO) with Mn2+ ions and the oxidation of ammonium ions (to N2) with MnO2. (a) Write balanced chemical equations for these reactions (in acid solution). (b) Calculate Ecell for the reactions. (One half-reaction potential you need is for the reduction of N2 to NH4+, E = 0.272 V.)

A voltaic cell is constructed in which one half-cell consists of a silver wire in an aqueous solution of AgNO3.The other half cell consists of an inert platinum wire in an aqueous solution containing Fe2+(aq) and Fe3+(aq). (a) Calculate the cell potential, assuming standard conditions. (b) Write the net ionic equation for the reaction occurring in the cell. (c) Which electrode is the anode and which is the cathode? (d) If [Ag+] is 0.10 M, and [Fe2+] and [Fe3+] are both 1.0 M, what is the cell potential? Is the net cell reaction still that used in part (a)? If not, what is the net reaction under the new conditions?

An aqueous solution of an unknown salt of gold is electrolyzed by a current of 2.75 amps for 3.39 hours. The electroplating is carried out with an efficiency of 93.0%, resulting in a deposit of 21.221 g of gold. a How many faradays are required to deposit the gold? b What is the charge on the gold ions (based on your calculations)?

You have 1.0 M solutions of Al(NO3)3 and AgNO3 along with Al and Ag electrodes to construct a voltaic cell. The salt bridge contains a saturated solution of KCl. Complete the picture associated with this problem by a writing the symbols of the elements and ions in the appropriate areas (both solutions and electrodes). b identifying the anode and cathode. c indicating the direction of electron flow through the external circuit. d indicating the cell potential (assume standard conditions, with no current flowing). e writing the appropriate half-reaction under each of the containers. f indicating the direction of ion flow in the salt bridge. g identifying the species undergoing oxidation and reduction. h writing the balanced overall reaction for the cell.

Which of the changes below will increase the voltage of the following cell? Co|Co2+(0.010M)H+(0.010M)|H2(0.500atm)|Pt (a) Increase the volume of COCl2 solution from 100 mL to 300 mL. (b) Increase [H+] from 0.010 M to 0.500 M. (c) Increase the pressure of H2 from 0.500 atm to 1 atm. (d) Increase the mass of the Co electrode from 15 g to 25 g. (e) Increase [CO2+] from 0.010 M to 0.500 M.