A piece of Al with a surface area of 2.5 m2 is anodized to produce a film of Al₂O₃ that is 23 μm (23X10⁻⁶ m) thick.(a) How many coulombs flow through the cell in this process (assume that the density of the Al₂O₃ layer is 3.97 g/cm³)?

Respuesta :

The charge passed in anodizing is 1.3×10^6 C

Surface area and thickness is 2.5 m² and 23X10⁻⁶ m respectively. Calculate the volume of Al2O3 coating as show below:

Volume =Surface area x thickness

             =2.5 m²x (23×10⁻⁶ m)

             =5.8×10^-5 m³

Density of Al, is 3.97 g/cm³

Calculate the mass of aluminum as shown below:

Density= Mass/Volume

3.97 = Mass×1/5.8×10^-5 ×10^6

Mass = 2.3×10^2g

The anodization of Aluminum is as shown below:

4AI (s)+ 302 (g) → 2Al2/O3 (s)

Now, oxidation number of Al in Al2O3 is +3 whi that in Al is zero. So, one Al3+ gains three electron to form one atom of Al.

           Al (s)→ Al (s)+3e

Charge = 2.3×10^2× 6 × 9.65 × 10^6  /(101.95  × 1 × 1)

              =1.3×10^6 C

Hence the charge passed in anodizing is 1.3×10^6 C

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