Problem 14 - A Complete Resource Book in Chemistry for JEE Main

Question

Removal to basic oxide from metal before electroplating is known as (a) poling (b) galvanizing (c) pickling (d) anodizing

Step-by-Step Solution

Answer

The process is called pickling (option c).

Step 1: Understanding the Question

The question asks about the process used to remove basic oxides from metals before electroplating. We need to determine what this specific process is called.

Step 2: Analyzing the Options

Let's examine each option one by one: - **Poling**: A processing step typically used in metallurgy to remove impurities from molten metal, not specifically oxide removal. - **Galvanizing**: This involves coating steel or iron with zinc to prevent rusting; it doesn't involve oxide removal. - **Pickling**: This process involves treating metals with an acid solution to remove oxides and other impurities, which is done prior to processes like electroplating. - **Anodizing**: An electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts, not for removing oxides.

Step 3: Identifying the Correct Option

Given the analysis above, **pickling** is the correct process for removing basic oxides from metals before electroplating. It specifically involves using an acid solution to clean the metal surface.

Key Concepts

Oxide Removal

Before delving into electroplating, it's essential to understand the importance of oxide removal. Metal surfaces naturally form oxides when exposed to air, moisture, or other environmental factors. These oxides can be detrimental to processes like electroplating because they prevent the metal ions from properly adhering to the surface. Removing oxides ensures:

• Improved adhesion of plated metals
• Better conductivity
• Enhanced corrosion resistance

Oxide removal is typically performed using chemical methods and is essential for preparing the metal surface for subsequent treatments, like electroplating, to ensure a smooth and adherent coating.

Pickling Process

The pickling process is a widely used method for removing unwanted oxides from metal surfaces. It involves submerging the metal in an acid solution that effectively dissolves the oxides and other contaminants. The types of acids used can vary depending on the metal and the specific oxides present, but commonly include hydrochloric or sulfuric acid. During pickling:

• The acid reacts with the oxide layer, forming soluble compounds that can be washed away.
• Ensures the metal surface is clean and ready for subsequent treatments like electroplating.
• May involve the use of inhibitors to prevent excess metal dissolution during the process.

Pickling is essential for ensuring that the underlying metal is pristine and free of contaminants that could interfere with electroplating or other finishing processes.

Metal Surface Preparation

Effective metal surface preparation is the foundation of successful electroplating. It involves a series of steps designed to ensure that the metal is clean, smooth, and ready for the application of coatings. The preparation process typically includes:

• Cleaning: Removal of oils, greases, and other residues using solvents or alkaline cleaning agents.
• Pickling: As previously discussed, it involves the removal of oxides and scales through acidic solutions.
• Rinsing: To wash away any residual chemicals from cleaning and pickling.
• Polishing or Buffing: Enhances the surface finish for optimal plating results.

Each step in surface preparation is crucial for achieving a high-quality electroplated finish. Without thorough preparation, any impurities left on the surface could lead to defects or failure of the plated layer. This meticulous preparation process ensures that the metal surface is ready for reliable and durable electroplating.