Problem 105 - Chemistry: The Central Science

Question

If you were going to apply a small potential to a steel ship resting in the water as a means of inhibiting corrosion, would you apply a negative or a positive charge? Explain.

Step-by-Step Solution

Answer

To inhibit corrosion on a steel ship resting in water, a negative charge should be applied. This makes the steel ship act as a cathode, suppressing the oxidation (anodic) reaction that leads to corrosion. By applying a negative charge, we effectively utilize the principle of cathodic protection to prevent the metal surface from corroding.

Step 1: Identify the electrode reactions involved in corrosion

The primary reactions in the corrosion process are anodic and cathodic half-cell reactions. At the anode, metal atoms are oxidized to form metal ions that dissolve in the environment. At the cathode, reduction occurs, which can involve different reactants such as oxygen. The overall corrosion process involves the transfer of electrons from the anode to the cathode through the metal.

Step 2: Recognize the principle of cathodic protection

Cathodic protection is a technique used to prevent corrosion of a metal surface (like a steel ship in water) by making the metal surface act as a cathode and avoiding the anodic reaction (which leads to corrosion). This can be achieved by applying an external current or by connecting the protected metal to a more reactive (easily-corroded) metal called the sacrificial anode.

Step 3: Determine the type of charge that should be applied

The goal is to ensure that the steel ship acts as a cathode, which means that we want to suppress the oxidation (anodic) reaction that leads to corrosion. Hence, we should apply a negative charge to the steel ship, since this charge will force the metal to act as a cathode and inhibit any further corrosion.

Step 4: Conclusion

To inhibit corrosion on a steel ship resting in water, a negative charge should be applied. This will ensure that the steel ship acts as a cathode, suppressing the oxidation reaction that leads to corrosion.