Problem 45 - A Complete Resource Book in Chemistry for JEE Main

Question

Fear or excitement, generally causes one to breathe rapidly and it results in the decrease of \(\mathrm{CO}_{2}\) concentration in blood. In what way will it change the \(\mathrm{pH}\) of blood? (a) \(\mathrm{pH}\) will increase (b) \(\mathrm{pH}\) will decrease (c) no change (d) \(\mathrm{pH}\) will adjust to 7

Step-by-Step Solution

Answer

(a) \(\mathrm{pH}\) will increase.

Step 1: Understanding the Question

When a person breathes rapidly due to fear or excitement, the body's respiratory rate increases. This causes excessive expulsion of carbon dioxide (\(\mathrm{CO}_{2}\) from the blood.

Step 2: Relation Between CO2 and pH

Carbon dioxide (\(\mathrm{CO}_{2}\)) in the blood contributes to acidity. It dissolves in blood to form carbonic acid (\(\mathrm{H}_2\mathrm{CO}_3\)), which dissociates into bicarbonate (\(\mathrm{HCO}_3^-\)) and hydrogen ions (\(\mathrm{H}^+\)). More \(\mathrm{H}^+\) results in lower pH (more acidic).

Step 3: Effect of Decreased CO2

As a consequence of rapid breathing, less \(\mathrm{CO}_{2}\) is available to form carbonic acid because it's being expelled quickly. Fewer hydrogen ions are produced, leading to a decrease in acidity.

Step 4: Determining the Change in pH

With decreased acidity, the pH of the blood increases, as pH is inversely related to the concentration of hydrogen ions.

Key Concepts

Respiratory Rate

When you catch a sudden feeling of excitement or fear, your body responds by rapidly increasing your breathing rate. This is known as an elevated respiratory rate.

• Rapid breathing has a significant effect on the chemical balances in your blood.
• As you breathe faster, more carbon dioxide (\( \text{CO}_2 \)) is expelled from your body.

This process may sound harmless, but it has a direct influence on how acidic or basic your blood is. Your body uses carbon dioxide as a tool to maintain a stable and healthy environment. So, understanding the link between respiratory rate and blood chemistry is essential!

Carbon Dioxide and Acidity

Carbon dioxide isn't just a byproduct of breathing. It plays a critical role in maintaining the acidity of your blood. When \( \text{CO}_2 \) is in the blood, it reacts with water to form carbonic acid (\( \text{H}_2\text{CO}_3 \)).

• This carbonic acid can then dissociate into hydrogen ions (\( \text{H}^+ \)) and bicarbonate (\( \text{HCO}_3^- \)).
• The presence of more hydrogen ions means the blood becomes more acidic, resulting in a lower pH.

When you breathe rapidly, the \( \text{CO}_2 \) levels in your blood drop because it's being expelled more quickly. As a consequence, less carbonic acid is formed, reducing the number of hydrogen ions. This ultimately leads to an increase in the pH, meaning the blood becomes less acidic.

Hydrogen Ion Concentration

Hydrogen ions are central to the concept of acidity. The concentration of hydrogen ions in your blood determines its pH level. The relationship is quite specific:

• If there's an increase in hydrogen ions, the pH decreases (becomes more acidic).
• If there's a decrease in hydrogen ions, the pH increases (becomes more basic or alkaline).

During periods of rapid breathing, as seen in excitement or fear, the decrease in carbon dioxide leads to fewer hydrogen ions being produced. This results in an elevated pH, making the blood slightly less acidic and more alkaline in nature. It's fascinating how our body uses such intricate mechanisms to keep our internal environment stable.