Problem 13 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Lead pencil contains (a) \(\mathrm{Pb}\) (b) \(\mathrm{FeS}\) (c) Graphite (d) \(\mathrm{PbS}\)

Step-by-Step Solution

Answer

Lead pencils contain graphite.

Step 1: Understanding Lead Pencils

Lead pencils are commonly misunderstood to contain lead due to their name. However, they do not actually contain the element lead (Pb). Historically, they were called lead pencils because the graphite in pencils was mistakenly thought to be a form of lead.

Step 2: Identifying Components of Lead Pencils

Lead pencils do not contain any lead compounds or lead elements like Pb, FeS, or PbS. Instead, they are made of a mixture that primarily includes graphite, which is a form of carbon.

Step 3: Verifying the Correct Answer

Given the options, only graphite is a component of the pencil's core. The other options (Pb, FeS, PbS) are not found in lead pencils. Therefore, the correct answer is graphite.

Key Concepts

Composition of Lead Pencils

Lead pencils are a staple in schools and offices, but their name is somewhat misleading. The term "lead pencil" is a historical misnomer. In actuality, the core of a lead pencil is made of a mixture of graphite and clay. This combination is what gives the pencil its writing capability. The clay acts as a binder, creating the specific hardness or softness of the pencil's mark on paper.

• Graphite: A form of carbon that is soft and easily leaves marks on paper.
• Clay: Mixed with graphite to adjust the hardness of the pencil.
The proportion of graphite to clay determines the pencil's grade. More graphite results in softer pencils, which produce darker marks, labeled "B" grades. Conversely, more clay results in harder pencils, which produce lighter marks, labeled "H" grades.

Misconceptions about Lead in Pencils

A common misconception is that lead pencils contain the metallic element lead (Pb). This belief originated centuries ago when the use of graphite was first discovered in England. At that time, it was thought to be a form of lead, and thus pencils were called "lead pencils."

However, this belief is incorrect. Modern lead pencils have never contained lead as part of their core composition. Instead, they use graphite, a non-toxic material. This is an important distinction, especially considering health concerns and regulations. Graphite is safe to handle and use and doesn’t pose the toxic risks associated with lead exposure.

The term "lead pencil" persists today primarily due to its historical roots rather than its actual material content.

Graphite as a Form of Carbon

Graphite is a fascinating substance, scientifically classified as a form of carbon. It is composed of carbon atoms arranged in a hexagonal structure, giving it several unique properties. Unlike other carbon-based materials, such as diamond, graphite is soft and slippery.

This softness results from the layers of carbon atoms in graphite that can easily slide over each other. This feature makes graphite an excellent writing material, enabling pencils to smoothly leave markings on paper.

Another interesting aspect of graphite is its ability to conduct electricity. Despite being a non-metallic material, its atomic structure allows electrons to move freely within its layers. This property makes graphite useful beyond writing applications, such as being used in batteries and as a lubricant in various industries.