Read Callister, Chapters 17 and 18. Solve and hand in Problems 17.6, 17.14, 17.35, 17.37, 18.11, 18.14, 18.20, and 18.53; due date Wednesday March 10.

Question 17.6

A Zn/Zn2+ concentration cell is constructed in which both electrodes are pure zinc. The Zn2+ concentration for one cell half is 1.0 M, for the other, 10-2M. Is a voltage generated between the two cell halves? If so, how big is it and which electrode will be oxidized? If, on the other hand, you don't think any voltage will be produced, explain why not.

Question 17.14

A thick steel sheet of area 64,500 mm2 is exposed to air near the ocean. After a one-year period, it was found to experience a weight loss of 485 gm due to corrosion. To what rate of corrosion, in mm/year, does this correspond ?

Question 17.35

According to Table 17.3 (6th edition), the oxide coating that forms on silver should be nonprotective, but in fact silver does not oxidise appreciably in air at room temperature. How do you explain this apparent discrepancy?

Question 17.37

The following table gives weight-gain vs. time data for the oxidation of a certain metal at an elevated temperature:

W (mg/cm2) Time (min)
6.16 100
8.59 250
12.72 1000

  1. Determine whether the oxidation kinetics obey a linear, parabolic or logarithmic rate expression.
  2. Compute W after a time of 5,000 minutes.

Question 18.11

Calculate the drift velocity of electrons in germanium at room temperature and when the magnitude of the electric field is 1000 V/m. Under these circumstances how long does it take an electron to traverse a 25-mm length of crystal?

Question 18.14

  1. Calculate the number of free electrons per cubic metre for silver, assuming there are 1.3 free electrons per silver atom. The electrical conductivity and density of silver are 6.8 * 107 per ohm-metre and 10.5 gm/cm3 respectively.

  2. Now calculate the electron mobility for silver.

Question 18.20

A cylindrical wire 2 mm in diameter is required to carry a current of 10 A with a maximum 0.01 V drop per 100 mm of wire. Which of the metals and alloys listed in Table 18.1 (6th edition) are candidates?

NOTE: In Callister, this question asks for a minimum 0.01 V drop per 100 mm, but this doesn't seem like a realistic requirement; if any voltage drop greater than 0.01 V per 100 mm is acceptable, you might as well leave the wire out entirely and increase the voltage until you get an arc.

Question 18.53

At temperatures between 540 C and 727 C, the activation energy and pre-exponential for the diffusion coefficient of Na+ in NaCl are 173,000 J/mol and 4.0 * 10-4 m2/s, respectively. Compute the mobility for an Na+ ion at 600 C.