Problem 150 - A Complete Resource Book in Chemistry for JEE Main

Question

Silver is a soft metal. It is hardened by alloying it with small amounts of (a) \(\mathrm{Cu}\) (b) \(\overline{\mathrm{Fe}}\) (c) \(\mathrm{Ni}\) (d) \(\mathrm{Sn}\)

Step-by-Step Solution

Answer

Copper (Cu) is used to harden silver by alloying.

Step 1: Understanding Silver Alloying

Silver is often alloyed with other metals to improve its hardness and durability while maintaining its aesthetic qualities. This process generally involves mixing silver with a small amount of another metal.

Step 2: Possible Alloying Elements for Silver

The common metals used for alloying with silver include copper (Cu), nickel (Ni), and sometimes zinc, but not typically iron (Fe) or tin (Sn). Alloying with copper is the most prevalent method because it strengthens silver without significantly altering its color or other desirable properties.

Step 3: Evaluating the Given Options

Looking at the given options: (a) Cu (Copper) (b) Fe (Iron) (c) Ni (Nickel) (d) Sn (Tin) Copper (Cu) and Nickel (Ni) are known to be commonly used to alloy silver for hardening purposes.

Step 4: Choosing the Most Common Option

While both copper and nickel are used for alloying with silver, copper is the classical and most common choice. Sterling silver, for example, is usually 92.5% silver and 7.5% copper.

Key Concepts

Metallurgy

Metallurgy is the science and technology of metals. It involves the study and practice of removing metals from their ores and preparing them for use. The primary goal of metallurgy is to produce metals with desired properties, suitable for various applications. Metallurgy encompasses several processes: mining, extraction, refining, alloying, and fabrication.
One of the essential aspects of metallurgy is understanding how different metals can be combined or "alloyed" to create materials with enhanced mechanical and chemical properties. For example, pure silver, known for its lustrous appearance and excellent conductivity, is too soft for many practical applications. By alloying silver with other metals, its properties can be modified to create materials more suitable for making jewelry, tableware, and industrial components.
The metallurgical processes not only address the durability of metals but also improve their resistance to corrosion, tensile strength, and thermal properties. Through careful selection and manipulation of alloying elements, manufacturers can tailor metal characteristics to meet specific requirements.

Metal Hardening

Metal hardening is a process used to enhance the mechanical properties of metals, especially their strength and durability. Hardening is particularly important for materials that will be subjected to stress, wear, and tear in their applications. Commonly, soft metals like silver are alloyed with small quantities of other harder metals to improve their hardness. This method is effective because it alters the metal's crystalline structure. When you introduce different atoms into the metal's lattice, they inhibit the movement of dislocations, which in turn strengthens the material.
Several techniques exist to harden metals:

• Alloying: Introducing other metals (like copper or nickel into silver) to create a more robust compound.
• Heat treatment: Such as annealing, quenching, or tempering, can also be employed to further manipulate the properties of the metal.
• Work Hardening: This involves deforming the metal at a temperature below its recrystallization point, thereby increasing its hardness.

By understanding these methods, materials scientists and engineers can enhance metal performance to meet the demands of different industrial and decorative applications.

Sterling Silver Composition

Sterling silver is a popular alloy known for its beauty and durability. Traditionally, sterling silver comprises 92.5% pure silver and 7.5% copper. This composition is carefully chosen to exploit the desirable properties of both metals while minimizing potential downsides.
Silver, while naturally beautiful and resistant to tarnish, lacks hardness. Adding copper helps to rectify this without drastically altering silver’s other qualities. Copper contributes strength and durability, essential for items like jewelry and cutlery that undergo frequent use. When discussing sterling silver, it's notable that the addition of copper doesn't significantly affect its ability to conduct heat or electricity, which are inherent qualities of silver. Moreover, the slight amount of copper ensures the metal retains its signature shine.
Understanding the composition of sterling silver helps consumers and manufacturers alike balance aesthetics with practicality. Despite exposure to the environment, items made from sterling silver maintain their integrity, making them a premium choice for many.