Biochemistry: Chapter 3
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Questions and Answers

What is the pKa value of Cacodylic acid?

  • 6.2 (correct)
  • 6.5
  • 7.0
  • 6.0

    • What is the major role of the phosphate buffer system?

  • Regulating body temperature
  • Promoting enzymatic reactions
  • Facilitating respiration
  • Stabilizing blood pH (correct)

    • Which acid has a conjugate base with a pKa of 3.75?

  • Lactic acid
  • Propanoic acid
  • Formic acid (correct)
  • Acetic acid

    • In the phosphate buffer system, what is the ratio of HPO4^2- to H2PO4^- at pH 7.4?

    <p>4:1</p> Signup and view all the answers

    Which of the following is NOT a physiological buffer system mentioned?

    <p>Carbon dioxide system</p> Signup and view all the answers

    What is the pKa for the imidazole buffer?

    <p>7.0</p> Signup and view all the answers

    What is the correct expression for the equilibrium constant (Keq) in terms of acid dissociation constant (Ka)?

    <p>Keq = Ka = [HA]/([A-][H+])</p> Signup and view all the answers

    Which weak acid has a conjugate base that is involved in buffering at pKa 12.4?

    <p>H3PO4</p> Signup and view all the answers

    What is the effect of bicarbonate in the carbonic acid/bicarbonate system?

    <p>It can act as both a proton donor and acceptor.</p> Signup and view all the answers

    How would you describe a buffer system in terms of its components?

    <p>A weak acid and its conjugated base</p> Signup and view all the answers

    Which weak acid has a pKa value closest to 4.76?

    <p>Acetic acid</p> Signup and view all the answers

    What is the pH of a solution if the concentration of the proton donor is 0.01 M and the concentration of the conjugated base is also 0.01 M with pKa being 4.76?

    <p>4.76</p> Signup and view all the answers

    What is the primary component of the phosphate buffer system?

    <p>H2PO4-/HPO42-</p> Signup and view all the answers

    In calculating the pH of weak acid solutions, if the Ka for acetic acid (CH3COOH) is 1.74 x 10^-5, which aspect is crucial for determining the concentration of H+?

    <p>The values of both [A-] and [HA] in the reaction</p> Signup and view all the answers

    What is the primary function of buffers in biological systems?

    <p>To resist changes in pH</p> Signup and view all the answers

    Which of the following solutions would you expect to have a higher pH than the physiological pH of blood (7.4)?

    <p>Pancreatic secretions</p> Signup and view all the answers

    When utilizing the Henderson-Hasselbalch equation, what is the relationship between pH, pKa, and the ratios of acid and base forms?

    <p>pH = pKa + log([A-]/[HA])</p> Signup and view all the answers

    Which of the following statements accurately describes the effect of pH on biochemical processes?

    <p>Small changes in pH can significantly alter reaction rates.</p> Signup and view all the answers

    If the dissociation constant (Ka) of a weak acid is increased, what would be the expected impact on the pH of its solution?

    <p>pH would decrease</p> Signup and view all the answers

    When applying the Henderson-Hasselbalch equation, what does a lower pKa indicate about the acid?

    <p>The acid has a higher tendency to dissociate.</p> Signup and view all the answers

    What does a high concentration of hydronium ions ($H_3O^+$) indicate about a solution?

    <p>It is an acidic solution.</p> Signup and view all the answers

    Which of the following represents the correct relationship between pH and pOH in a solution?

    <p>pH + pOH = 14</p> Signup and view all the answers

    What term is used for a pair of compounds where one acts as a proton donor and the other as a proton acceptor?

    <p>Conjugate acid-base pair</p> Signup and view all the answers

    In the dissociation of acetic acid ($CH_3COOH$), what is the conjugate base formed?

    <p>$CH_3COO^-$</p> Signup and view all the answers

    Which of the following describes a characteristic of weak acids?

    <p>They partially dissociate in aqueous solutions.</p> Signup and view all the answers

    What is the ion product of water ($K_w$) at 25°C?

    <p>$1 x 10^{-14} M^2$</p> Signup and view all the answers

    In water, what is the concentration of hydroxide ions ($OH^-$) at pH 7?

    <p>$1 x 10^{-7} M$</p> Signup and view all the answers

    Which of the following substances is classified as a strong acid?

    <p>Hydrochloric acid</p> Signup and view all the answers

    What does the term 'proton hopping' refer to?

    <p>The rapid movement of protons in solutions.</p> Signup and view all the answers

    Which indicator dye is best for detecting pH changes in acidic solutions?

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

    What is the combined equilibrium constant (Kcombined) for the reactions involving carbonic acid and bicarbonate?

    <p>8.1 x 10-7</p> Signup and view all the answers

    How does the addition of 1 ml of 10 N NaOH affect the pH of the buffer made from NaH2PO4 and Na2HPO4?

    <p>It increases pH to 7.2</p> Signup and view all the answers

    What is the ratio of HCO3- to H2CO3 in the buffer system at a pH of 7.4?

    <p>20/1</p> Signup and view all the answers

    What is the expected final pH when 1 ml of 10 N NaOH is added to 1 liter of pure water with an initial pH of 7.0?

    <p>12</p> Signup and view all the answers

    What is the value of pKa given that pKa is 6.86 in the context of the buffer system?

    <p>6.86</p> Signup and view all the answers

    Which component of the buffer system represents the weak acid?

    <p>NaH2PO4</p> Signup and view all the answers

    What is the concentration of OH- produced when 1 ml of 10 N NaOH is added to pure water?

    <p>0.01 M</p> Signup and view all the answers

    What is the equilibrium constant for the dissociation of carbonic acid (Ka)?

    <p>2.7 x 10-4</p> Signup and view all the answers

    If the pKa of a buffer system is 6.86, what is the pH when the concentration of the conjugate base is twice that of the acid?

    <p>7.86</p> Signup and view all the answers

    What effect does increasing the concentration of the conjugate base have on the buffer system's pH?

    <p>Increases pH</p> Signup and view all the answers

    Study Notes

    Ionization/Dissociation of Water

    • Water dissociates into hydrogen ions (H+) and hydroxide ions (OH-)
    • The equilibrium constant (Keq) for the dissociation of water is 1.8 x 10^-16 M
    • The ion product of water (Kw) is 1 x 10^-14 M2
    • In pure water at 25°C, the concentration of [H+] and [OH-] are both 1 x 10^-7 M

    pH and pOH

    • pH is the negative logarithm of the hydrogen ion concentration: pH = -log10[H+]
    • pOH is the negative logarithm of the hydroxide ion concentration: pOH = -log10[OH-]
    • The sum of pH and pOH is always 14: pH + pOH = 14

    Weak Acids & Bases

    • Strong acids like hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3) are completely ionized in dilute aqueous solutions.
    • Strong bases like sodium hydroxide (NaOH) and potassium hydroxide (KOH) are completely ionized.
    • Weak acids and bases dissociate partially in solution, with a characteristic acid dissociation constant (Ka).
    • Stronger acids have a greater tendency to lose their proton.
    • The Henderson-Hasselbalch equation relates the pH of a solution to the pKa of the acid and the ratio of the concentrations of the acid and its conjugate base.

    Calculating the pH of Weak Acids

    • The Ka value is used to calculate the concentration of hydrogen ions ([H+])
    • The pH of a weak acid solution is calculated using the Henderson-Hasselbalch equation.

    Buffers

    • Buffers resist changes in pH when small amounts of acid or base are added.
    • A buffer system consists of a weak acid (proton donor) and its conjugate base (proton acceptor).
    • The pH of a buffer solution is calculated using the Henderson-Hasselbalch equation.

    Physiological Buffer Systems

    • Hemoglobin is a major buffer in the blood.
    • Proteins act as non-bicarbonate buffers.
    • Phosphate buffer system is important for intracellular buffering.
    • Carbonic acid-bicarbonate buffer system is the primary buffer system in blood.

    Phosphate Buffer System

    • The pKa of the phosphate buffer system is 6.86.
    • The ratio of HPO42- to H2PO4- in the blood is about 4:1.

    Carbonic Acid-Bicarbonate Buffer System

    • The carbonic acid-bicarbonate buffer system is responsible for maintaining blood pH.
    • This system involves the reversible reaction between CO2 and H2O to form carbonic acid (H2CO3).
    • The pKcombined for this buffer system is 6.1.
    • The ratio of HCO3- to H2CO3 in blood is about 20:1.

    Questions & Answers

    • Question 1: The pH of a mixture of 0.042 M NaH2PO4 and 0.058 M Na2HPO4 is 7.0.
    • Question 2: Adding 1 ml of 10 N NaOH to a liter of the buffer prepared in Question 1 increases the pH by 0.2 units, to 7.2.
    • Question 3: Adding 1 ml of 10 N NaOH to a liter of pure water increases the pH to 12.

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    Description

    Explore the concepts of water ionization, pH, and pOH through this quiz. Understand the dissociation of water and the behavior of strong and weak acids and bases. Test your knowledge on key equations and constants related to acid-base chemistry.

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