Problem 18 - Chemistry The Science in Context

Question

In the following pairs, which element is more abundant in the human body? (a) H or \(\mathrm{Si} ;\) (b) Ca or \(\mathrm{Fe} ;\) (c) \(\mathrm{N}\) or \(\mathrm{Cr}\)

Step-by-Step Solution

Answer

Answer: (a) Hydrogen (H), (b) Calcium (Ca), (c) Nitrogen (N)

Step 1: Pair (a) Comparison: H or Si

To identify which element - Hydrogen (H) or Silicon (Si) - is more abundant in the human body, we will compare their corresponding percentages. According to scientific data, Hydrogen composes approximately 10% of the human body by mass, while Silicon composes only about 0.026%.

Step 2: Answer for Pair (a)

As 10% (Hydrogen) is greater than 0.026% (Silicon), Hydrogen (H) is more abundant in the human body than Silicon (Si).

Step 3: Pair (b) Comparison: Ca or Fe

Next, we compare Calcium (Ca) and Iron (Fe) to identify which element is more abundant in the human body. Calcium composes approximately 1.5% of the human body by mass, whereas Iron composes about 0.006%.

Step 4: Answer for Pair (b)

Since 1.5% (Calcium) is greater than 0.006% (Iron), Calcium (Ca) is more abundant in the human body than Iron (Fe).

Step 5: Pair (c) Comparison: N or Cr

Lastly, we compare Nitrogen (N) and Chromium (Cr) to determine which element is more abundant in the human body. Nitrogen composes approximately 2.5% of the human body by mass, while Chromium composes only around 0.00025%.

Step 6: Answer for Pair (c)

As 2.5% (Nitrogen) is greater than 0.00025% (Chromium), Nitrogen (N) is more abundant in the human body than Chromium (Cr). To summarize, for each pair of elements: - (a) Hydrogen (H) is more abundant than Silicon (Si) - (b) Calcium (Ca) is more abundant than Iron (Fe) - (c) Nitrogen (N) is more abundant than Chromium (Cr)

Key Concepts

Understanding the human body composition

The human body is a complex system comprised of various elements that play essential roles in maintaining life processes. Although the body is made up of many different substances, only a few elements make up the majority of its mass. These elements include Oxygen (O), Carbon (C), Hydrogen (H), Nitrogen (N), Calcium (Ca), and Phosphorus (P).
Together, they account for more than 99% of the human body's mass.

When we talk about human body composition, it essentially reflects the proportion of these elements.

• Oxygen is the most abundant element in the human body, making up about 65% of the body's mass.
• Carbon follows, accounting for roughly 18%.
• Hydrogen comes next with approximately 10% of the body's mass.
• Nitrogen, another critical element, makes up about 2.5%.

These elements are present in different forms in various tissues and contribute to the body's structure and function. For example, Calcium is a significant part of bones and teeth, whereas Oxygen and Hydrogen are vital components of water, the most abundant compound in the body.

Elements comparison in human body

When understanding how elements are present in the human body, it's useful to compare them by their relative abundance.
This fundamental knowledge helps in studying biological and chemical functions within the body. By examining pairwise comparisons, we can better appreciate which elements are more prevalent.

For instance, in comparing elements:

• Hydrogen (H) versus Silicon (Si): Hydrogen is significantly more abundant, making up about 10% of body mass, whereas Silicon is only 0.026%.
• Calcium (Ca) versus Iron (Fe): Calcium is more prevalent, composing 1.5% of body mass, compared to Iron's 0.006%.
• Nitrogen (N) versus Chromium (Cr): Nitrogen is more abundant at 2.5%, while Chromium is a mere 0.00025%.

The relative abundances mirror the elements' roles in physiological processes. For instance, Hydrogen is essential in bonding with Carbon to form organic molecules, while Iron, though less abundant, is crucial for oxygen transport in blood.

Explaining elemental percentages

Elemental percentages in the human body help in expressing the proportionate mass of each element relative to the entire body. This method provides a clear way to quantify how much of a certain element is present.
Rather than just listing elements, percentages give context to their roles and significance.

The calculation of these percentages involves dividing the amount of the element's mass by the total body mass and then multiplying the result by 100. This results in a percentage value that indicates its relative abundance. To understand why some elements are more present than others, consider:

• Oxygen: Dominates because it forms water and is part of almost all organic molecules.
• Carbon: Essential for all life as it forms the backbone of all organic molecules.
• Calcium: Important for bone structure, contributing to a higher percentage.

This representation is critical in fields like medicine and biology, where understanding the element's function is key. For example, knowing the high percentage of Calcium can lead to better bone health insights, while the lower percentages of elements like Iron show they must be well managed for functions like hemoglobin production.