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Practice Exam Solutions

# Practice Exam Solutions - 1 Balance the following equation...

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1) Balance the following equation in an acidic solution: CH 3 OH(aq) + Ce 4+ (aq) ° CO 2 (aq) + Ce 3+ H 2 O + CH 3 OH + 6Ce 4+ ° 6Ce 3+ + 6H + + CO 2 2) Balance the following equation in a basic solution: H 2 CO(aq) + Ag(NH 3 ) 2 + (aq) ° HCO 3 - (aq) + Ag(s) + NH 3 (aq) 5OH - + H 2 CO + 4Ag(NH 3 ) 2 + ° 4Ag + HCO 3 - + 3H 2 O + 8NH 3 3) Why is a salt bridge or porous disk necessary for the flow of electrons in a galvanic cell? A salt bridge or porous disk allows charge balance (it prevents charge build-up). 4) For the following unbalanced equation: Cu 2+ (aq) + Mg(s) ? Mg 2+ + Cu(s) Draw a spontaneous galvanic cell labeling the anode, cathode, electron flow direction, + and – signs, electrodes, and solutions. Assume the concentrations are 1M and T=298K. In addition, write the balanced equation, cell diagram, overall cell potential, equilibrium constant, ?G°, and specify how many electrons are transferred. Cu 2+ + Mg ° Mg 2+ + Cu x ° = +2.7 Mg¦ Mg 2+ ¦ Cu 2+ ¦ Cu (note I drew a porous disk, it could also be a salt bridge¦ ) ?G° = -nF x ° = -521 kJ/mol Solve for K by lnK = (nF x °)/(RT) I don’t have a calculator with me, but everything is known except K. 2 electrons are transferred per mole as seen by n = 2 from the total reaction. Cu 2+ Mg 2+ Cu Mg Anode (-) e - e - Cathode(+)

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