pH and Buffering Concepts

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Questions and Answers

What is the main function of buffers in bodily fluids?

To facilitate the breakdown of proteins

To resist rapid changes in pH (correct)

To completely eliminate acids from the body

To increase the temperature of body fluids

What is pKa, and why is it important in biological buffering?

It reflects the protonation state of a buffering agent at a specific pH (correct)

It indicates the strength of an acid in terms of its complete dissociation

It is the pH at which a weak acid is completely dissociated

It demonstrates the rate of reaction of acids with bases

What is the normal pH range for human blood?

7.0 to 7.8

7.0 to 8.0

6.5 to 7.0

7.35 to 7.45 (correct)

Which of the following is a consequence of acidosis?

Decreased protein synthesis Signup and view all the answers

Which organs are primarily responsible for regulating acid-base balance in the body?

Lungs and kidneys Signup and view all the answers

What role do proteins serve in physiological buffering?

They can donate or accept protons depending on pH changes Signup and view all the answers

How do hemoglobin molecules function as buffers in the blood?

By releasing protons when carbon dioxide is loaded Signup and view all the answers

Which of the following components primarily generates acids in the human body?

Breakdown of proteins and fats Signup and view all the answers

What is the effect of an increase in pH on hydroxide ion concentration?

Hydroxide ion concentration increases Signup and view all the answers

At what pH level does the concentration of hydrogen ions equal that of hydroxide ions?

pH 7 Signup and view all the answers

Which of the following describes a strong acid?

Completely dissociates in solution Signup and view all the answers

Which statement correctly describes the dissociation of water?

Water dissociates to a very small extent Signup and view all the answers

What is the formula relating hydrogen ion concentration and pH?

pH = - log [H+] Signup and view all the answers

What does the pKa value indicate about an acid?

It is the pH at which the acid is half dissociated. Signup and view all the answers

Which statement accurately describes the relationship between pKa and acid strength?

The lower the pKa, the stronger the acid. Signup and view all the answers

When the hydrogen ion concentration is $10^{-2}$ M, what is the corresponding pH value?

pH 2 Signup and view all the answers

Which of the following correctly describes weak acids?

Dissociate incompletely depending on pH Signup and view all the answers

In the context of buffers, what occurs at the pKa of a weak acid?

Equal concentrations of the acid and its conjugate base are present. Signup and view all the answers

What is the purpose of the Henderson-Hasselbalch equation?

To relate pH, pKa, and the concentration of acid and conjugate base. Signup and view all the answers

What is the ionic product of water at neutrality?

$[H+] = [OH-] = 10^{-7}$ Signup and view all the answers

During the titration of phosphoric acid with KOH, what species is produced upon complete dissociation?

PO4^3- Signup and view all the answers

Which of the following correctly describes a weak acid?

It exists primarily in the non-dissociated form in solution. Signup and view all the answers

What is the dissociation constant (Ka) a measure of?

The strength of an acid and its ability to donate protons. Signup and view all the answers

When titrating with NaOH, what is the primary factor that changes the pH?

The amount of conjugate base formed during the reaction. Signup and view all the answers

Which pKa value indicates that deoxyhaemoglobin is a weaker acid compared to oxyhaemoglobin?

7.8 Signup and view all the answers

What is the base/acid ratio for oxyhaemoglobin at a blood pH of 7.4?

3.98:1 Signup and view all the answers

At which pH value does aspirin diffuse more easily across biological membranes?

pH 2 Signup and view all the answers

What effect do neighboring groups have on the pKa of histidine in hemoglobin compared to free histidine?

They increase the pKa value. Signup and view all the answers

What is the pKa of oxyhaemoglobin, and how does it relate to its buffering capacity for H+?

6.8; it becomes a less effective buffer at lower pH. Signup and view all the answers

What log ratio for deoxyhaemoglobin indicates a higher acid concentration compared to a base concentration at a blood pH of 7.4?

-0.4 Signup and view all the answers

What happens when H+ ions are added to a buffer system?

They can be picked up by the conjugate base. Signup and view all the answers

Which physiological buffer system has a pKa value closest to neutral pH?

H2PO4- → HPO42- Signup and view all the answers

Why is glycine a poor physiological buffer?

Its buffering occurs at too low a pH. Signup and view all the answers

What determines the buffering effectiveness of an acid at a specific pH?

The concentration of its conjugate base. Signup and view all the answers

What characteristic of hemoglobin contributes to its role as a buffer in blood?

The presence of a significant number of histidine residues. Signup and view all the answers

What does the Henderson-Hasselbalch equation primarily express?

The relationship between pH and pKa of a buffer system. Signup and view all the answers

Which amino acid group does not contribute effectively to physiological buffering?

Alpha carboxyl groups. Signup and view all the answers

Which form of carbonic acid is dominant when regulating blood pH?

HCO3- at neutral pH. Signup and view all the answers

Study Notes

pH and its Measurement

pH indicates the concentration of hydrogen ions in a solution, influencing its acidity or alkalinity.
True acidity is determined by free hydrogen ions, not those bound to anions.
Normal blood pH ranges from 7.35 to 7.45; levels outside this can be dangerous (acidosis <7.35, alkalosis >7.45).

Sources of Acids in the Body

Acids mainly originate from:
- Breakdown of proteins
- Incomplete oxidation of fats and glucose
- Transport of carbon dioxide in the blood
The body regulates acid-base balance through the lungs, kidneys, and chemical buffer systems.

Buffering System

Buffers stabilize pH by:
- Releasing hydrogen ions as acids when pH rises
- Binding hydrogen ions as bases when pH drops
Ideal buffering occurs at the pKa where acid and conjugate base are present in equal amounts.

Understanding Acids and Bases

Strong acids fully dissociate (e.g., HCl → H+ + Cl-), while weak acids partially dissociate (e.g., H2CO3 → H+ + HCO3-).
Strong bases are more effective proton acceptors than weak bases.

Water Ionization

Pure water is a 55.6M solution and dissociates slightly into H+ and OH- ions.
At neutrality, both [H+] and [OH-] equal 10^-7 M, yielding a pH of 7.

pKa and its Importance

pKa is the negative logarithm of the dissociation constant (Ka); it indicates the pH at which an acid is half dissociated.
The lower the pKa, the stronger the acid.

Henderson-Hasselbalch Equation

Formula: pH = pKa + log([A-]/[HA])
This equation connects pH, pKa, and the concentrations of an acid and its conjugate base, guiding buffer capacity.

Physiological Buffers

Key physiological buffers include:
- H2CO3 ↔ HCO3- (pKa 6.1)
- H2PO4- ↔ HPO42- (pKa 6.8)
- Proteins also function as buffers, with a specific dependence on amino acid side chains.

Role of Amino Acids

Glycine's buffering capacity is limited outside its pKa values (2.34 and 9.66).
The active buffering in physiological conditions is largely attributed to R groups of amino acids.

Hemoglobin as a Buffer

Hemoglobin effectively buffers H+ produced during metabolism due to its histidine residues.
The pKa of histidine in hemoglobin is altered by neighboring groups:
- Oxyhemoglobin has a pKa of 6.8
- Deoxyhemoglobin has a pKa of 7.8

Analyzing Hemoglobin's Buffering Capacity

For normal blood pH (7.4):
- OxyHb with pKa 6.8 provides a ratio of base/acid (3.98:1).
- DeoxyHb with pKa 7.8 has a ratio of 1:2.51, making oxyhemoglobin a better buffer for metabolic acid.

Diffusion of Lipid-soluble Molecules

Lipid-soluble substances can easily diffuse across biological membranes, while those strongly interacting with water struggle to do so.
Aspirin diffusion is affected by pH, diffusing more readily at pH 8 than at pH 2.

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Description

This quiz evaluates your understanding of pH and buffering, focusing on the differences between strong and weak acids, the significance of pKa, and the application of the Henderson-Hasselbalch equation. Additionally, it covers physiological buffers and the role of proteins and hemoglobin in buffering systems. Test your knowledge on these essential topics in biology and chemistry.