Problem 95 - A Complete Resource Book in Chemistry for JEE Main

Question

Lead impurity is removed from silver by? (a) distillation (b) poling (c) lavigation (d) cupellation

Step-by-Step Solution

Answer

Lead impurity is removed from silver by cupellation.

Step 1: Understanding the Methods

First, we need to understand what each method entails: - **Distillation** involves heating a liquid and collecting the vapor. - **Poling** is a process used in metallurgy to purify metals. - **Lavigation** involves washing the ore. - **Cupellation** is a refining process in which air is blown across a molten metal to cause oxidizable impurities to oxidize.

Step 2: Analyzing the Impurity

Lead is a common impurity in silver mining. We need a method that can specifically remove lead, which can be oxidized.

Step 3: Selecting the Correct Method

Cupellation works well for purifying silver by removing lead. In this method, lead oxidizes to form lead oxide which is easily separated from the silver.

Key Concepts

Lead Impurities

Lead is often found as an impurity in silver due to its natural occurrence in lead-silver ores. Impurities like lead in precious metals can affect the quality and usability of the metal. Understanding how impurities such as lead end up in silver helps us choose the right purification methods.
Lead can be detrimental for a number of reasons:

• **Decreases Metal Purity**: It reduces the overall quality and value of the metal.
• **Affects Metal Properties**: It can alter properties like melting point and structural integrity.

Removing lead from silver is critical to achieving high purity. The process must effectively remove oxidizable elements to leave behind pure silver. Methods like cupellation are essential to tackle this specific type of impurity.

Silver Refining

Refining silver is all about achieving the highest level of purity possible. It involves carefully selecting methods to remove different impurities that naturally occur alongside silver in ores.
Let's break down the process:

• **Preliminary Steps**: Initial steps may involve concentration of silver, removing bulk waste materials.
• **Use of Chemical Processes**: Subjecting the silver to specific chemical processes to dissolve unwanted materials.
• **Application of Physical Methods**: These include melting and heating which can also aid in separation processes.

Refining isn't just removing visible impurities; it is about achieving a chemical integrity that gives silver its desirable properties. One of the specialized processes for purifying silver is the cupellation method which specifically targets lead impurities.

Cupellation Process

Cupellation is a tried and tested method used in metallurgy, particularly effective for refining precious metals like silver. The cupellation process effectively removes lead and other oxidizable impurities, leaving behind pure silver.
This method is distinctive due to its:

• **Use of High Temperatures**: Heating the metal encourages the oxidation of lead and other impurities.
• **Air Flow Mechanism**: Air is blown over the molten metal enhancing the oxidation process.
• **Formation of Lead Oxide**: The oxidized lead forms a slag of lead oxide which can be separated.

Thanks to its efficiency in removing specific impurities like lead, cupellation remains a popular refining method in metallurgy. It's an effective way to ensure that the silver we use is of the highest quality and purity, which is crucial in both industrial and ornamental settings.