In applied electrochemistry, the process of depositing a thin layer of a desired metal onto the surface of another material by using an electric current is called what?

Introduction / Context:
Electrochemical processes are widely used in industry to modify the surfaces of metals and other materials. One very common process is the use of electric current to deposit a thin, decorative or protective layer of one metal onto another object. This technique improves appearance, corrosion resistance, and surface hardness. The question asks for the correct name of this process, which is important in both chemistry and manufacturing technology.

Given Data / Assumptions:

• The process involves depositing a desired metal layer on another material.
• Electric current is used to drive the deposition from a solution containing metal ions.
• The options listed are electroplating, galvanisation, rusting, and crystallisation.
• We assume the usual definitions from school level chemistry for these processes.

Concept / Approach:
Electroplating is defined as the process in which a metal object is used as a cathode in an electrolytic cell, and a solution containing ions of the coating metal is used as an electrolyte. When electric current passes through the cell, metal cations are reduced and deposit on the object as a thin metallic coating. Galvanisation is a specific process where iron or steel is coated with zinc, usually by dipping in molten zinc, to prevent rusting. Rusting is the slow oxidation of iron in the presence of water and oxygen, and crystallisation is a physical process used to obtain pure crystals from a solution. Only electroplating matches the description of using electricity to deposit a metal layer on another surface in a general sense.

Step-by-Step Solution:
Step 1: Identify the key features described: a layer of metal is deposited on another material using electricity. Step 2: Recall that in electroplating, the object to be coated is connected to the negative terminal of a power source and acts as the cathode. Step 3: Recognise that the electrolyte solution contains ions of the metal to be deposited, such as silver ions for silver plating. Step 4: Understand that when current flows, metal ions gain electrons at the cathode and are deposited as a thin layer on the surface. Step 5: Note that galvanisation refers specifically to coating iron or steel with zinc and does not describe the general process for any metal. Step 6: Conclude that the general name for the described process is electroplating and select electroplating as the correct option.

Verification / Alternative check:
Textbooks and industrial descriptions of surface finishing processes use the term electroplating for a wide range of applications, including chromium plating on car parts, silver plating on jewellery, and nickel plating for corrosion resistance. In each case, an electric current is used to move metal ions from the solution onto the object. Galvanisation is always discussed separately as a hot dipping process, not as a generic term for electrical deposition. Rusting is treated as an undesirable corrosion process, and crystallisation as a method of purification of solids. These distinctions confirm that electroplating is the only option that fits the description given in the question.

Why Other Options Are Wrong:
Galvanisation is limited primarily to coating iron or steel with zinc and does not always involve electrolysis in the sense described; it often uses molten zinc baths. Rusting is a corrosion process where iron reacts with oxygen and moisture to form iron oxides and is not a controlled deposition method. Crystallisation is a method used to obtain pure solid crystals from solution and does not involve depositing a metallic layer by electric current. None of these processes matches the general concept of electrically depositing a layer of any desired metal onto another surface.

Common Pitfalls:
Students sometimes confuse galvanisation and electroplating, assuming both are identical because both involve coatings. The key difference is that galvanisation is a specific protective coating with zinc, whereas electroplating is a broader technique that can use many different metals and relies on electrolytic deposition. Another pitfall is to mix up any process involving metals and solutions with electroplating, without checking whether an electric current is used. Always look for explicit use of electricity and deposition of a metal layer, which signals electroplating.

Final Answer:
The process of depositing a metal layer on another material using electric current is called electroplating of the metal onto the surface.