Question

When pieces of human hair are heated strongly with soda-lime, smell of ammonia can be detected. Which one of the following conclusion can be drawn from this observation? (a) Hair contains amino acids (b) Ammonium salt is present in hair (c) Ammonia is present in the human hair (d) None of the above

Short answer

(a) Hair contains amino acids.

Step-by-step solution

Identify the Components in Hair

Human hair is primarily composed of a protein called keratin, which is made up of amino acids. These amino acids contain nitrogen, a key element in various compounds including ammonia.

Analyze Heating Process Result

When human hair is heated strongly with soda-lime, chemical reactions occur in which nitrogen present in amino acids and proteins can be released in the form of ammonia gas, creating the observed smell.

Link Observation to Conclusions

The smell of ammonia indicates the presence of amino groups in the structure of the hair, which are part of amino acids or proteins in hair. The reaction with soda-lime liberates ammonia from these nitrogen-containing compounds.

Assess Given Options

Given the smell of ammonia upon heating with soda-lime, the most direct conclusion is that the hair contains amino acids. This is because the release of ammonia is due to the breakdown of nitrogen-containing components, namely amino acids, present in the hair.

Key concepts

Keratin Structure

Keratin is a fibrous protein that forms the main structural component of human hair. It provides strength and protection. Imagine keratin as a tightly woven fabric, where each thread represents an amino acid. This structure gives hair its resilience and flexibility.

Keratin is rich in a type of amino acids called "cysteines." These amino acids contain sulfur, which forms disulfide bonds, acting like strong bridges connecting different parts of the weave. This interlocking network of bonds is key to keratin's strength. When you look closely at a strand of hair, you're seeing this complex arrangement that allows hair to withstand constant brushing or styling.

Furthermore, keratin is not a simple, uniform structure. It consists of alpha-helix and beta-sheet configurations. The alpha-helix is a spiral that stretches and recoils, much like a spring, while the beta-sheet resembles a folded ribbon. This combination of structures in keratin contributes to the varied properties of human hair, such as its elasticity and texture.

Ammonia Production in Chemical Reactions

When you heat human hair with soda-lime, a significant chemical reaction occurs. This process can lead to the production of ammonia gas. Here's why:

• Hair contains keratin, a protein rich in amino acids, which include nitrogen elements.
• Soda-lime acts as a base and as a catalyst that drives the decomposition of these amino acids, especially when heat is applied.
• The heat encourages the breakdown of nitrogen-containing components, resulting in the release of ammonia—a compound with a pungent smell.

This reaction is a prime example of how heat can catalyze changes in compounds containing nitrogen groups. Ammonia production is a clear indicator of the presence of such nitrogen-based structures in materials like hair.

Protein Composition in Hair

Human hair is primarily made up of protein, with keratin being the most abundant. This protein composition is complex and built from a multitude of amino acids. Here are some interesting tidbits:

• Amino acids, which are the building blocks of proteins, contain elements like carbon, hydrogen, oxygen, and nitrogen.
• The nitrogen in amino acids forms the backbone of protein structures, contributing significantly to the functionality and properties of hair.
• When proteins like keratin break down, especially under heat and in the presence of reactants like soda-lime, the nitrogen component can be released, often as ammonia gas.

Understanding the protein composition of hair helps explain not only its physical properties but also the chemical reactions it undergoes. This knowledge is crucial in fields ranging from hair care to forensic science, as it reveals how durable and chemically active hair proteins really are.