Electrochemistry

80. (Concentration gradient, diffusion) Demonstration: A pair of cupric ion solutions, one concentrated and dark blue and the other dilute and light blue, are separated by a removable barrier. What will happen when the barrier is removed?

the solutions retain their respective colors, the dark solution becomes darker and the light solution becomes lighter, the solutions become indistinguishable in color

The entropy of the system will

increase, decrease, stay the same


The enthalpy of the system will

increase, decrease, stay the same

81. (Concentration cells) Refer to the figure below. What is the spontaneous direction of the system?

Cu2+ (in 1 M soln.) ---> Cu(s) and Cu(s) --->Cu2+ (in 0.01 M soln.),
Cu2+ (in 0.01 M soln.) ---> Cu(s) and Cu(s) --->Cu2+ (in 1 M soln.)

Will a voltage be measured?

yes, no

If the pictured solutions are mixed and then divided into separate cells, will a voltage be measured?

yes, no

When unmixed, in which direction do the electrons travel when current is allowed to flow?

right, left

To which cell will the positively charged ions in the salt bridge flow?

right, left

Demonstration: With a concentration cell, demonstrate the answers to each of the questions above.

82. (Galvanic cells, redox, Le Châtelier's principle)

Ag+ + e- --->Ag E°= 0.80 V;
Cu2+ + 2e- ---> Cu E°= 0.34 V

Will Ag react with Cu2+?

yes, no

Will Cu react with Ag+?

yes, no

Demonstration: Cu + 2 Ag+ ---> Cu2+ + 2 Ag Place a sheet of copper into a AgNO3 solution. The submerged copper will be plated with silver at the end of the reaction.
Demonstration: Construct a galvanic cell:
Measure the voltage.
If water is added to the Cu2+ cell, how will the voltage be affected?

voltage will increase, voltage will decrease, no change

If ammonia is added to the Cu2+ cell to form an amine complex, how will the voltage be affected?

voltage will increase, voltage will decrease, no change

If Cl- solution is added to the Ag+ half cell to precipitate AgCl, how will the voltage be affected?

voltage will increase, voltage will decrease, no change

As current passes, the voltage

increases, decreases, stays constant

127. (Concentration cell, semiconductors, doping; Ch. 8 "Companion") To minimize diffusion of a dopant into a semiconductor, heat

at low temperature for a short time, at high temperature for a long time

Which way do electrons want to go in a p-n junction to establish equilibrium?

n-type side to p-type side, p-type side to n-type side

Which p-n junction will give the larger voltage?

A, B

Consider a p-n junction formed by ZnSe (band gap 2.7 eV) and GaAs (band gap 1.4 eV). Which side of the junction is ZnSe?

left, right

Which side of the junction is p-type?

left, right

206. If the reduction of mercury (I) in a voltaic cell is desired, the half reaction is:

Which of the following reactions could be used as the anode (oxidation)?

A, B

212. A concentration cell is made, having Ag electrodes immersed in AgNO3 solutions of different concentrations. When the two cell compartments have AgNO3 concentration of 1 M and 0.1 M, the measured voltage is 0.06 V. What will the voltage be if the two compartments have AgNO3 concentrations of 1 M and 0.01 M?

zero volts
0.03 volts
0.06 volts
0.12 volts

238. Both leads of an LED conductivity probe are dipped in water, dried, and then dipped in mercury. In which liquid(s) will the LED light up?

H2O, Hg, both, neither




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