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A metal rod of 3 cm diameter and 20 cm length is placed in a solution of hydrochloric acid with a pH of 2 at 25°C. The metal has a critical pitting temperature of 40°C and a standard electrode potential of -0.44V. Assuming that the rod is polarized to a potential of -0.50V, what is the corrosion current density (in mA/cm²) of the metal in the given environment?

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To calculate the corrosion current density, we can use the Tafel equation, which relates the overpotential  difference between the actual electrode potential and the standard electrode potential  to the corrosion current density. The Tafel equation is: =  * log i / i where  is the overpotential,  is the Tafel slope  typically around 0.12 V/decade for many metals , i is the corrosion current density, and i is the exchange current density.First, we need to calculate the overpotential   : = E - Ewhere E is the actual electrode potential  -0.50 V  and E is the standard electrode potential  -0.44 V . = -0.50 -  -0.44  = -0.06 VNow we can rearrange the Tafel equation to solve for the corrosion current density  i :i = i * 10^ /  We don't have the value of i, but we can estimate it based on the pH of the solution. For a pH of 2, the H concentration is 10^-2  mol/L. Assuming a typical exchange current density of 10^-6  A/cm for each 1 mol/L of H, we can estimate i as:i = 10^-6  * 10^-2  = 10^-8  A/cmNow we can plug in the values into the equation:i = 10^-8  * 10^-0.06 / 0.12 i = 10^-8  * 10^-0.5 i = 10^-8.5  A/cmTo convert A/cm to mA/cm, we multiply by 1000:i = 10^-8.5  * 1000i  0.000316 mA/cmSo, the corrosion current density of the metal in the given environment is approximately 0.000316 mA/cm.

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