CHEM 210 Exam Questions and Correct Answers

CHEM 210 Exam Questions and Correct Answers What is a cathode? - Answer-a negative electrode at which reduction occurs What is an anode? - Answer-the positive electrode at which oxidation occurs Good way to remember which is which for anode and cathode - Answer-An Ox and a Red Cat What is the two electrode setup? - Answer-anode and cathode What is a galvanic cell? - Answer-A cell in which spontaneous oxidation-reduction reactions produce electrical energy (anode and cathode Zn and Cu) What is an electrolytic cell? - Answer-uses electrical energy to drive a non-spontaneous reaction (our reaction) What is the 3 electrode setup? - Answer-working electrode, counter electrode, reference electrode How do you find the half cell potential? - Answer-A half cell potential can't be measured by itself. The oxidation of hydrogen gas to H+ (as well as the reverse reduction of H+ to H2) has ∆G˚f values of zero, and accordingly it must also have zero potential. Therefore, constructing a whole cell using a H2/H+ half-cell for one of the half reactions and measuring the whole cell potential must be equal solely to the potential of the second half reaction. Many reaction potentials are found this way. H2(g) ⇄ 2 H+(aq) + 2e- E1/2 = 0.00V I2 (s) + 2e- ⇄ 2 I- (aq) E1/2 = 0.54V Four points about half cell potentials - Answer-By convention, the half-cell reactions are always listed as reductions and are balanced! The half-reactions are written with double arrows, noting their reversibility. Reversing its direction (to be an oxidation), reverses the sign of E˚1/2. E˚1/2 are usually given to two decimal places. Most importantly, when constructing working voltaic cells, the reductive half reaction listed higher in the table (more positive E˚1/2) remains as the reduction, while the half cell reaction lower in the table is reversed and becomes the oxidative reaction.