AP Chemistry Unit 9 Electrochemistry

Two different electrolytic cells are constructed to electroplate two identical objects based on the half reactions given in the table above.  Which of the following mathematical relationships can be used to determine how much more current is needed to electroplate an object with Au than to electroplate it with Ag?

• The difference in standard reduction potential of Au3+ and Ag+

  is 0.70V.

• Three times more electrons are needed to reduce Au3+(aq)

  to Au(s) than are needed to reduce Ag+(aq) to Ag(s).

• ΔG° is more negative for the reduction of Au3+(aq)

  to Au(s) than for the reduction of Ag+(aq) to Ag(s).

The diagrams above illustrate the equipment used to electroplate four identical objects with silver or zinc. The table provides the conditions used. Which of the following provides the basis for the identification of the object that requires the highest current, I, to complete the electroplating?

• Object 1, based on the molar mass of Ag and the time of operation.

• Object 2, based on the molar mass of Ag and the time of operation.

• Object 3, based on the coulombs of charge needed and the time of operation.

• Object 4, based on the coulombs of charge needed and the time of operation.

Tags

NGSS.HS-PS3-1

Two identical spoons were electroplated with Ag

or Cd through the use of the electrolytic cells illustrated above. A current of 5.00A was supplied to each cell for 600. seconds, and the masses of the spoons before and after the electroplating were recorded. Which of the following mathematical equations can best be used to account for the much larger increase in mass of the spoon electroplated with Ag compared with the spoon electroplated with Cd?

• ΔG°=ΔH°−TΔS°

• ΔG°=−RTlnK

• E=E°−(RT/nF)lnQ

• I=q/t

Ni2+(aq)+Cd(s)→Ni(s)+Cd2+(aq)

E°cell=+0.15V

Under standard conditions, a Ni-Cd galvanic cell generates a potential of +0.15V using the chemical reaction represented above. Which of the following best explains how [Ni2+]>1M affects the cell potential if this is the only change made to the operation of the galvanic cell?

• The ratio [Cd2+]/[Ni2+] is smaller if [Ni2+]>1M, resulting in Q<1

  Q<1 and Ecell>E°cell.

• The ratio [Cd2+]/[Ni2+] is smaller if [Ni2+]>1M resulting in Q>1

  and Ecell>E°cell.

• The ratio [Ni2+]/[Cd2+] is larger if [Ni2+]>1M, resulting in Q>1 and Ecell<E°cell.

• The ratio [Ni2+]/[Cd2+] is larger if [Ni2+]>1M, resulting in Q<1 and Ecell<E°cell.

Tags

NGSS.HS-PS1-5

The reaction represented by the equation above serves as the basis for the construction of an electrochemical cell. The table gives the reduction half-reactions and their respective standard reduction potentials. Based on the overall reaction, which type of electrochemical cell was constructed, and why?

• A galvanic or voltaic cell, because the standard reduction potentials for the two half-reactions are positive and E°cell=0.80+0.34=+1.14V.

• A galvanic or voltaic cell, because the standard reduction potentials for the two half-reactions are positive and E°cell=0.80−0.34=+0.46V

• An electrolytic cell, because ΔG=−(96,500×(−0.46))/1000 =44kJ/mol and its operation requires a potential smaller than 0.46V to be supplied.

• An electrolytic cell, because ΔG=−(2×96,500×(−0.46))/1000 = 89 kJ/mol and its operation requires a potential greater than 0.46V to be supplied.

Tags

NGSS.HS-PS1-2

NGSS.HS-PS1-4

The operation of a hydrogen fuel cell under standard conditions relies on the chemical reaction represented above. The table provides the relevant reduction half-reactions and the standard reduction potentials. Based on the information given, which of the following equations can be used to calculate the standard reduction potential, in volts, of the half-reaction occurring at the cathode?

Tags

NGSS.HS-PS3-1

A galvanic cell was constructed using a salt bridge containing KNO₃. A second cell is constructed from identical half-cells but uses NaNO₃ for the salt bridge. Which of the following best explains whether the initial potential of the second cell will be different from the initial potential of the first cell?

• The initial potential of the second cell will be lower than the initial potential of the first cell because Na has a lower molar mass than K has.

• The initial potential of the second cell will be higher than the initial potential of the first cell because Na is less electronegative than K is.

• The initial potential of the second cell will be the same as the first cell because the ions from the salt bridge are not oxidized or reduced during cell operation.

• The initial potential of the second cell will be higher than the initial potential of the first cell because Na is less electronegative than K is.

The reaction in which H₂O(l) is decomposed into H₂(g)

and O₂(g) is thermodynamically unfavorable (ΔG°>0). However, an electrolytic cell, such as the one represented above, can be used to make the reaction occur. Which of the following identifies a flaw in the representation?

• oxidation is occurring at the anode

• the equation is not correctly balanced

• Electrical energy is needed for the reaction to proceed

• The volumes of collected gas in each tube should not be the same.

Tags

NGSS.HS-PS1-4

The particle diagrams above represent NaCl(l)

and its decomposition into Na(l) and Cl₂(g) in an electrochemical cell after voltage is applied. Which of the following statements about the thermodynamic favorability of the decomposition of NaCl(l)

is supported by the particle diagrams and why?

• The decomposition is thermodynamically favored because the transfer of electrons to and from the ions occurs at the electrodes.

• The decomposition is thermodynamically favored because the formation of a gaseous product results in an increase in entropy.

• The decomposition is not thermodynamically favored because the pure elements form only after electrical energy is supplied.

• The decomposition is not thermodynamically favored because there is a decrease in the number of particles as the reaction proceeds.

Tags

NGSS.HS-PS1-4

The chemical equations above represent the main reactions that occur during the production of Fe(l) under certain conditions. The overall reaction couples reactions 1 and 2, resulting in a thermodynamically favorable process. Which of the following best explains whether or not a particle diagram could represent how the coupling of reaction 1 and reaction 2 results in ΔG°<0?

• A particle diagram that represents the increase in the volume of gaseous product particles would be a good representation of how the coupling of reactions 1 and 2 results in a thermodynamically favorable process.

• A particle diagram that represents the decrease in the average kinetic energy of the particles would be a good representation of how the coupling of reactions 1 and 2 results in a thermodynamically favorable process.

• A particle diagram cannot represent how the changes in energy that take place as reaction 1 occurs are more than offset by the changes in energy taking place as reaction 2 occurs, resulting in a thermodynamically favorable overall reaction.

• A particle diagram cannot represent the changes in the amount of matter that take place as reaction 1 is coupled to reaction 2, resulting in a thermodynamically favorable overall reaction.

Tags

NGSS.HS-PS1-4