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.

Short answer

To inhibit corrosion in a steel ship resting in water, a negative charge should be applied. This is because we want the steel to behave as if it were a cathode, attracting the positively charged external anode and preventing the steel from losing electrons and corroding. The technique used to achieve this is called cathodic protection.

Step-by-step solution

Understanding Corrosion and Electrochemistry

Corrosion is a naturally occurring process where metal reacts with its environment, typically leading to material degradation. It is an electrochemical process, which involves the transfer of electrons from one species to another, forming a galvanic cell. In the case of a steel ship in water, the steel serves as an anode, where metal ions are released into the environment as electrons are lost. Those electrons transfer to a cathode, usually oxygen gas or water molecules, leading to a decrease in the steel's integrity.

Cathodic Protection

To prevent corrosion, we can use a technique called cathodic protection. The idea is to connect the metal (steel in this case) to an external anode, which will provide the electrons instead of the steel. This way, the steel will not lose electrons and will not corrode.

Applying a Charge

To determine whether to apply a positive or negative charge to the steel ship, we need to consider the behavior of the anode and cathode in the galvanic cell. The anode provides electrons (oxidation) and carries a positive charge, while the cathode receives electrons (reduction) and carries a negative charge.

Preventing Corrosion

To inhibit corrosion in a steel ship resting in water, we want the steel to behave as if it were a cathode, meaning we need to apply a negative charge to the ship. This negative charge will attract the positively charged anode (the external source providing electrons) and prevent the steel from losing electrons and corroding. So, the answer is to apply a negative charge on the steel ship to inhibit corrosion.