38 Questions
What is the primary function of buffers in the body?
To resist abrupt and large swings in the pH of body fluids
Which of the following is NOT a source of acids in the body?
Ingestion of alkali-rich foods
What is the normal pH range of blood?
7.35-7.45
Which system in the body plays a crucial role in regulating acid-base balance?
Respiratory system
What is the term for a condition where the blood pH is below 7.35?
Acidosis
What is the function of hemoglobin in the body?
To act as a buffer for hydrogen ions
What is the term for a condition where the blood pH is above 7.45?
Alkalosis
What is the term that describes the ability of an acid to release H+ ions?
pKa
What is the ionic product of water at neutrality?
10^-14 M2
What is the pH of a solution with a hydrogen ion concentration of 10^-2 M?
2
What is the percentage of water in the body of a healthy young woman?
50%
What is the characteristic of a strong acid?
Dissociates completely in solution
What is the pH of blood?
7.4
What is the relationship between [H+] and [OH-] when [H+] = 10^-2 M?
[OH-] = 10^-12 M
What is the characteristic of a weak base?
Is a less effective proton acceptor
What is the pH of a solution when [H+] = 3.98 x 10^-8 M?
7.4
What is the significance of pKa in the context of acid dissociation?
It represents the pH at which the acid is half dissociated
What is the consequence of adding acid or alkali to a buffer solution at the pKa?
The pH of the solution remains relatively constant
What is the relationship between the pKa of a weak acid and its strength?
The lower the pKa, the stronger the acid
In a titration curve, what does the point of inflection represent?
The point at which the acid is half dissociated
What is the purpose of the Henderson-Hasselbalch equation?
To relate the pH of a solution to the pKa of a weak acid
At what pH does buffering occur best?
At a pH equal to the pKa
What is the significance of the conjugate base in a buffer solution?
It is the basic form of the buffer
What is the role of phosphoric acid in the context of acid-base chemistry?
It is a weak acid that partially dissociates in water
What is the main reason why the pKa of histidine in Hb is different from that of free His?
Due to the presence of other groups in the vicinity
Which of the following is a better buffer for H+ produced in metabolism and why?
Oxyhaemoglobin, because it has a pKa value closer to the pH of blood
What is the ratio of base to acid in oxyhaemoglobin at a pH of 7.4?
3.98:1
What can be predicted about the diffusion of aspirin across biological membranes?
It diffuses more easily at pH 2 than pH 7
What is the relationship between the pH of blood and the pKa of oxyhaemoglobin?
The pH of blood is 0.6 units higher than the pKa of oxyhaemoglobin
What is the significance of the Henderson-Hasselbalch equation in the context of acid-base balance?
It helps to calculate the pH of a buffer solution
What is the role of the conjugate base in a buffer system?
To pick up excess H+ ions
At what pH does a buffer system buffer best?
At a pH equal to the pKa
What is the significance of the Henderson-Hasselbalch equation in buffer systems?
It is used to calculate the pH of a buffer system
Why is glycine not a good candidate for physiological buffering?
Because it buffers best at pH 2.3 and 9.6
What is the importance of histidine residues in haemoglobin?
They are important for the buffering capacity of haemoglobin
What is the role of H2CO3 in physiological buffering?
It is a buffer that maintains the pH of blood
Why are amino acid side chains not good physiological buffers?
Because their pKa is outside the physiological range
What is the significance of the pKa value of an acid in a buffer system?
It determines the buffering capacity of the acid
Study Notes
pH and Buffering
- pH is a measure of hydrogen ion concentration in a solution, which determines the acidity or alkalinity of the solution.
- pH is a critical parameter in the body, with a normal range of 7.35 to 7.45 in blood, and a living range of 7.0 to 7.8.
Acidity in the Body
- Acids in the body come from food and the breakdown of proteins, incomplete oxidation of fats or glucose, and the loading and transport of carbon dioxide in the blood.
- Acid-base balance is regulated in the body by the lungs, kidneys, and chemical buffers in the blood.
Buffering
- Buffers resist abrupt and large swings in the pH of body fluids by releasing H+ (acting as acids) when the pH rises and binding H+ (acting as bases) when the pH drops.
- Buffers operate by releasing or binding H+ ions to maintain a stable pH.
Strong and Weak Acids and Bases
- Strong acids and bases are completely dissociated in solution, whereas weak acids and bases are only partially dissociated.
- The strength of an acid or base is determined by its dissociation constant (Ka).
pKa and its Importance
- pKa is the negative logarithm of the dissociation constant (Ka) of an acid.
- pKa is a measure of the strength of an acid, with lower pKa values indicating stronger acids.
- pKa is important in biological buffering because it determines the pH at which an acid is half-dissociated.
Henderson-Hasselbalch Equation
- The Henderson-Hasselbalch equation relates the pH of a solution, the pKa of a weak acid, and the relative amounts of dissociated and non-dissociated forms of the acid.
- The equation is: pH = pKa + log ([A-]/[HA])
Physiological Buffers
- Physiological buffers are mixtures of weak acids and their conjugate bases that help maintain a stable pH in the body.
- Examples of physiological buffers include H2CO3/HCO3-, H2PO4-/HPO42-, and proteins.
Haemoglobin as a Buffer
- Haemoglobin is an important buffer in the blood, particularly in the physiological range.
- The presence of histidine residues in haemoglobin makes it a good buffer for H+ ions produced in metabolism.
- The pKa of histidine in haemoglobin is different from that of free histidine, due to the presence of neighbouring groups.
Importance of Haemoglobin in Buffering
- Oxyhaemoglobin is a better buffer for H+ ions produced in metabolism than deoxyhaemoglobin, due to its lower pKa value.
- The ratio of base to acid in oxyhaemoglobin is 3.98:1, while in deoxyhaemoglobin it is 1:2.51.
Learn about pH, buffering and its importance in biological systems, including strong and weak acids, pKa, Henderson-Hasselbalch equation, and physiological buffers like Haemoglobin.
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