Problem 141 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following sulphides are yellow? (a) \(\mathrm{As}_{2} \mathrm{~S}_{3}\) (b) \(\mathrm{ZnS}\) (c) \(\mathrm{CdS}\) (d) \(\mathrm{SnS}_{2}\)

Step-by-Step Solution

Answer

The yellow sulfides are (a) \(\mathrm{As}_{2} \mathrm{~S}_{3}\), (c) \(\mathrm{CdS}\), and (d) \(\mathrm{SnS}_{2}\).

Step 1: Review the sulfides

Identify the chemical formulas given: (a) Arsenic sulfide is \(\mathrm{As}_{2} \mathrm{~S}_{3}\), (b) Zinc sulfide is \(\mathrm{ZnS}\), (c) Cadmium sulfide is \(\mathrm{CdS}\), and (d) Tin sulfide is \(\mathrm{SnS}_{2}\). Recognize that the color of a sulfide can help identify it.

Step 2: Recall color characteristics

Remember that certain metal sulfides have characteristic colors: \(\mathrm{As}_{2} \mathrm{~S}_{3}\) and \(\mathrm{SnS}_{2}\) are typically yellow due to arsenic and tin, \(\mathrm{CdS}\) is also known for being yellow, whereas \(\mathrm{ZnS}\) is typically white or grey.

Step 3: Compare with the question

Compare the given sulfides to the known color properties: \(\mathrm{As}_{2} \mathrm{~S}_{3}\), \(\mathrm{CdS}\), and \(\mathrm{SnS}_{2}\) are yellow, while \(\mathrm{ZnS}\) is not.

Step 4: Select the yellow sulfides

Conclude that the yellow sulfides are \(\mathrm{As}_{2} \mathrm{~S}_{3}\), \(\mathrm{CdS}\), and \(\mathrm{SnS}_{2}\).

Key Concepts

Arsenic Sulfide

Arsenic sulfide, known chemically as \( \mathrm{As}_{2} \mathrm{~S}_{3} \), is a fascinating compound not only for its striking yellow color but also due to its interesting properties. This compound occurs naturally as orpiment, a mineral that has been historically used as a pigment and a medicine. However, caution is advised, as arsenic compounds can be toxic if mishandled.
Arsenic sulfide is primarily used in the manufacturing of semiconductors and glass. Its brilliant yellow hue comes from the specific way sulfur and arsenic atoms absorb and reflect light.

• It possesses a melting point of 320°C.
• Having a vitreous luster, it appears shiny and glass-like.

Despite its instability in the presence of strong light and heat, arsenic sulfide remains an important compound in various industrial applications.

Cadmium Sulfide

Cadmium sulfide, represented by the formula \( \mathrm{CdS} \), is another yellow sulfide important in industrial and scientific applications. It is naturally found as the minerals greenockite and hawleyite.
Useful in electronic industries, cadmium sulfide is popular for its photoconductive properties. These properties make it crucial in creating light-sensitive devices, thin-film transistor detectors, and as a pigment in certain paints and plastics.

• Cadmium sulfide reacts with acids and alkalis.
• It has a melting point of roughly 980°C.

Though appreciated for its vibrant yellow color, the handling of cadmium sulfide requires caution due to the potential toxicity of cadmium.

Tin Sulfide

Tin sulfide, known by its formula \( \mathrm{SnS}_{2} \), is a compound drawing attention due to its characteristic yellow color and interesting properties. Naturally found as the mineral berndtite, tin sulfide is lesser known compared to its industrially prolific counterparts like arsenic and cadmium sulfides.
It is utilized in various areas, particularly in photovoltaic applications due to its ability to absorb sunlight effectively. Tin sulfide’s green credentials lie in its non-toxic nature compared to other sulfides.

• It has a high melting point of approximately 920°C.
• Tin sulfide boasts good thermoelectric and electro-optical properties.

These characteristics make tin sulfide a worthy material for sustainable energy solutions.

Sulfide Color Characteristics

The ability of sulfides to display striking and distinct colors plays a crucial role in their identification and application. These color characteristics are influenced by the interactions between metal ions and sulfur within their crystalline structures.
Commonly, yellow sulfides include arsenic sulfide (\( \mathrm{As}_{2} \mathrm{~S}_{3} \)), cadmium sulfide (\( \mathrm{CdS} \)), and tin sulfide (\( \mathrm{SnS}_{2} \)). These distinct hues arise not just as a visual attribute, but are also indicative of specific electronic and chemical properties.

• The yellow coloration typically results from the bandgap energies allowing visible light absorption.
• Variation in color can indicate purity levels and composition variations.

Understanding these color characteristics aids in the identification and utilization of metal sulfides across various chemical and industrial processes, making them a cornerstone in material sciences.