pH and Buffering in Biological Systems
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Questions and Answers

What is the primary function of buffers in the body?

  • To increase the pH of body fluids
  • To regulate the oxygen levels in the blood
  • To resist abrupt and large swings in the pH of body fluids (correct)
  • To generate acids in the body

    • Which of the following is NOT a source of acids in the body?

  • Breakdown of proteins
  • Ingestion of alkali-rich foods (correct)
  • Loading and transport of oxygen in the blood
  • Incomplete oxidation of fats or glucose

    • What is the normal pH range of blood?

  • 7.0-7.2
  • 7.2-7.4
  • 7.5-7.7
  • 7.35-7.45 (correct)

    • Which system in the body plays a crucial role in regulating acid-base balance?

    <p>Respiratory system</p> Signup and view all the answers

    What is the term for a condition where the blood pH is below 7.35?

    <p>Acidosis</p> Signup and view all the answers

    What is the function of hemoglobin in the body?

    <p>To act as a buffer for hydrogen ions</p> Signup and view all the answers

    What is the term for a condition where the blood pH is above 7.45?

    <p>Alkalosis</p> Signup and view all the answers

    What is the term that describes the ability of an acid to release H+ ions?

    <p>pKa</p> Signup and view all the answers

    What is the ionic product of water at neutrality?

    <p>10^-14 M2</p> Signup and view all the answers

    What is the pH of a solution with a hydrogen ion concentration of 10^-2 M?

    <p>2</p> Signup and view all the answers

    What is the percentage of water in the body of a healthy young woman?

    <p>50%</p> Signup and view all the answers

    What is the characteristic of a strong acid?

    <p>Dissociates completely in solution</p> Signup and view all the answers

    What is the pH of blood?

    <p>7.4</p> Signup and view all the answers

    What is the relationship between [H+] and [OH-] when [H+] = 10^-2 M?

    <p>[OH-] = 10^-12 M</p> Signup and view all the answers

    What is the characteristic of a weak base?

    <p>Is a less effective proton acceptor</p> Signup and view all the answers

    What is the pH of a solution when [H+] = 3.98 x 10^-8 M?

    <p>7.4</p> Signup and view all the answers

    What is the significance of pKa in the context of acid dissociation?

    <p>It represents the pH at which the acid is half dissociated</p> Signup and view all the answers

    What is the consequence of adding acid or alkali to a buffer solution at the pKa?

    <p>The pH of the solution remains relatively constant</p> Signup and view all the answers

    What is the relationship between the pKa of a weak acid and its strength?

    <p>The lower the pKa, the stronger the acid</p> Signup and view all the answers

    In a titration curve, what does the point of inflection represent?

    <p>The point at which the acid is half dissociated</p> Signup and view all the answers

    What is the purpose of the Henderson-Hasselbalch equation?

    <p>To relate the pH of a solution to the pKa of a weak acid</p> Signup and view all the answers

    At what pH does buffering occur best?

    <p>At a pH equal to the pKa</p> Signup and view all the answers

    What is the significance of the conjugate base in a buffer solution?

    <p>It is the basic form of the buffer</p> Signup and view all the answers

    What is the role of phosphoric acid in the context of acid-base chemistry?

    <p>It is a weak acid that partially dissociates in water</p> Signup and view all the answers

    What is the main reason why the pKa of histidine in Hb is different from that of free His?

    <p>Due to the presence of other groups in the vicinity</p> Signup and view all the answers

    Which of the following is a better buffer for H+ produced in metabolism and why?

    <p>Oxyhaemoglobin, because it has a pKa value closer to the pH of blood</p> Signup and view all the answers

    What is the ratio of base to acid in oxyhaemoglobin at a pH of 7.4?

    <p>3.98:1</p> Signup and view all the answers

    What can be predicted about the diffusion of aspirin across biological membranes?

    <p>It diffuses more easily at pH 2 than pH 7</p> Signup and view all the answers

    What is the relationship between the pH of blood and the pKa of oxyhaemoglobin?

    <p>The pH of blood is 0.6 units higher than the pKa of oxyhaemoglobin</p> Signup and view all the answers

    What is the significance of the Henderson-Hasselbalch equation in the context of acid-base balance?

    <p>It helps to calculate the pH of a buffer solution</p> Signup and view all the answers

    What is the role of the conjugate base in a buffer system?

    <p>To pick up excess H+ ions</p> Signup and view all the answers

    At what pH does a buffer system buffer best?

    <p>At a pH equal to the pKa</p> Signup and view all the answers

    What is the significance of the Henderson-Hasselbalch equation in buffer systems?

    <p>It is used to calculate the pH of a buffer system</p> Signup and view all the answers

    Why is glycine not a good candidate for physiological buffering?

    <p>Because it buffers best at pH 2.3 and 9.6</p> Signup and view all the answers

    What is the importance of histidine residues in haemoglobin?

    <p>They are important for the buffering capacity of haemoglobin</p> Signup and view all the answers

    What is the role of H2CO3 in physiological buffering?

    <p>It is a buffer that maintains the pH of blood</p> Signup and view all the answers

    Why are amino acid side chains not good physiological buffers?

    <p>Because their pKa is outside the physiological range</p> Signup and view all the answers

    What is the significance of the pKa value of an acid in a buffer system?

    <p>It determines the buffering capacity of the acid</p> Signup and view all the answers

    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.

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    Description

    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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