gen chem #3
if the surface area of electrode material in an electrochemical cell is tripled, what else is necessarily tripled? I. E cell II. Current III. Keq A. I only B. II only C. I and II only D. II and III only
B II. Current only remember E cell (potential) is an intensive property - value is not changed -dependent only on the ID of the electrodes and not the amount present -similarly, the eq constant depends only on the ID of the electrolyte solutions and the temp however, as the electrode material is increased, the surface area participating in redox rxns is increased so more e-s are released which increases current
which of the following compounds is LEAST likely to be found in the salt bridge of a galvanic cell? A. NaCl B. SO3 C. MgSO3 D. NH4NO3
B. SO3 salt bridges = need inert electrolytes (no ppt) - ionic compounds such as NaCL, MgSo3, and NH3No3 are known as strong electrolytes because they completely dissociate in solution B. SO3 cannot be considered an electrolyte b/c its atoms are covalently bonded and will not dissociate in aqueous solution SO3 and MgSO3 appear to be similar, BUT important distinction C. implies that Mg 2+ and So3 2- are the final dissociated ionic constituents B. implies the neutral So3 would have to be dissolved in solution --> NO!!
an electrolytic cell is filled with water. which of the following will move toward the cathode of such a cell? I. H+ ions II. O2- ions III. electrons a. I only b. II only c. I and III only d. II and III only
C III. electrons I. H+ ions remember electrons to cathode get reduced cations -> cathode (salt bridge) anions -> cathode (salt bridge) H+ = cation O2- = anion
The salt bridge is essential in maintaining electrical neutrality in a Daniell cell. In the absence of a salt bridge, the two compartments will accumulate the opposite charges and prevent further reaction. For the salt bridge to function properly, there must be an appropriate electrolyte. Which of the following statements most accurately explains whether an electrolyte is appropriate for the salt bridge in the following electrochemical cell? 2ag+ (aq) + Cu (2) -> 2 Ag(s) + Cu2+ (aq) a. koh is not a good choice because K has a very positive reduction potential b. k2So4 is not appropiate because polyatomic ions such as sulfate ion will oxidize more easily than water c. Kcl is not appropiate because this compound will react w/ the ions in the compartments d. CuS is a good choice bc neither the cation and anion will react w/ ions in the compartments
C. c. Kcl is not appropiate because this compound will react w/ the ions in the compartments -not good choice bc would react -> form ppt -> agcl (s) a. koh is not a good choice because K has a very positive reduction potential *positive reduction potential not relevant -KOH is not appropiate because hydroxide migrates towards the anode and reacts with Ag ion in solution -> makes ppt -> all OHs are insoluble b. k2So4 is not appropriate because polyatomic ions such as sulfate ion will oxidize more easily than water *oxidation of water not relevant here *actually a good choice bc soluble in water and the cation and anion do not react w/ ions d. CuS is a good choice bc neither the cation and anion will react w/ ions in the compartments Cus -> insoluble in water - so no ions would be able to migrate to the anode or cathode compartment to balance the charge
if the value of E cell is already known, what additional info is needed to calculate delta G? A. gas constant (R) B. reaction quotient C. temp D. half rxns of the cell
D. half rxns of cell G = -nFE F = constant E = have -need n -to determine n, need to look at balanced half-rxns occuring at the redox rxn
which of the following can alter the EMF of an electrochemical cell? a. mass of the electrodes b. length of the wire connecting the half cells c. overall size of the battery d. temp of the solutions in the half cells
d. temp of the solutions in the half cells g = -nfe g = - rt ln k eq rt ln keq = nfe
