A thick wall made of natural rubber is exposed to pure oxygen gas on one side of

Question:

A thick wall made of natural rubber is exposed to pure oxygen gas on one side of its surface. Both the wall and oxygen gas are isothermal at 25°C, and the oxygen concentration at the wall surface is constant. Determine the time required for the oxygen concentration at x = 5 mm to reach 5% of its concentration at the wall surface. Oxygen gas 0 I 5 mm 1-- Rubber wall X