Glass etching is an important industrial process that uses caustic solutions to dissolve the outer layer of glass to remove surface defects resulting from the tempering process. Consider a cylindrical rod of glass that is very long relative to its cross-sectional diameter such that L >> D and of density p. Here, the glass can be approximated as pure silica (SiO2), and the reaction occurs only at the solid-liquid interface with area rate constant k. For simplicity, assume the amount of hydroxide is in excess and the solution is well-stirred to maintain a constant concentration of [OH] at the surface. L>> D Initial Diameter (Do) = 2 SiO2 cm k = 4*102 gsi02 (m psio2 = 2 g (cm)-1 *S Note: The rate constant units imply that the surface reaction is first-order with respect to [OH] only. a) Set up a differential equation for the rate of change of the diameter of the glass rod. b) How long does it take for the glass rod to reach a diameter of 1.9 cm?