Podcast
Questions and Answers
The Henderson-Hasselbalch equation is most useful for estimating the pH of solutions containing which of the following?
The Henderson-Hasselbalch equation is most useful for estimating the pH of solutions containing which of the following?
- A strong base and its conjugate acid.
- A strong acid and its conjugate base.
- A mixture of a strong acid and strong base.
- A weak acid and its conjugate base. (correct)
What is the primary reason the Henderson-Hasselbalch equation may not provide accurate pH values for strong acids or bases?
What is the primary reason the Henderson-Hasselbalch equation may not provide accurate pH values for strong acids or bases?
- It assumes the concentrations of the acid and conjugate base at equilibrium are the same as their formal concentrations. (correct)
- It does not account for the self-dissociation of water.
- It requires the use of activity coefficients, which are difficult to determine.
- It is only applicable at very high concentrations.
Which of the following is a limitation of the Henderson-Hasselbalch equation?
Which of the following is a limitation of the Henderson-Hasselbalch equation?
- It does not account for the effect of temperature on pH.
- It cannot be used for buffer solutions with pH values close to 7.
- It is only applicable when the concentrations of the acid and base are equal.
- It fails to provide accurate pH values for extremely dilute buffer solutions. (correct)
If the concentration of a weak acid (HA) is equal to the concentration of its conjugate base (A-), what does the Henderson-Hasselbalch equation predict about the pH of the solution?
If the concentration of a weak acid (HA) is equal to the concentration of its conjugate base (A-), what does the Henderson-Hasselbalch equation predict about the pH of the solution?
According to equilibrium principles, how does dissolving chlorine gas in a condensed solution of sodium hydroxide exemplify acid-base chemistry?
According to equilibrium principles, how does dissolving chlorine gas in a condensed solution of sodium hydroxide exemplify acid-base chemistry?
How are Ka (acid dissociation constant) and pKa related?
How are Ka (acid dissociation constant) and pKa related?
What does the Henderson-Hasselbalch equation help to determine besides the pH of a buffer solution?
What does the Henderson-Hasselbalch equation help to determine besides the pH of a buffer solution?
How would you best describe the behavior of a solid base like sodium hydroxide (NaOH) in solution?
How would you best describe the behavior of a solid base like sodium hydroxide (NaOH) in solution?
How does the precision of pKa compare to that of pH for determining the behavior of a molecule in solution?
How does the precision of pKa compare to that of pH for determining the behavior of a molecule in solution?
For calculating the pH of a buffer solution using the Henderson-Hasselbalch equation, which concentrations are required?
For calculating the pH of a buffer solution using the Henderson-Hasselbalch equation, which concentrations are required?
Flashcards
Henderson-Hasselbalch Equation
Henderson-Hasselbalch Equation
A mathematical expression relating pH, pKa, and the concentrations of acid and conjugate base in a solution.
pKa
pKa
The negative logarithm of the acid dissociation constant (Ka), indicating acid strength.
Buffer Solution
Buffer Solution
A solution that resists changes in pH upon addition of small amounts of acid or base.
pH
pH
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Acid Dissociation Constant (Ka)
Acid Dissociation Constant (Ka)
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Formal Concentration
Formal Concentration
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pKb
pKb
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Study Notes
- The Henderson-Hasselbalch equation relates the pH of solutions to their pKa.
- It can estimate a buffer solution's pH when the concentration of the acid and its conjugate base are known.
- The equation is written as: pH = pKa + log([A–]/[HA]), where [A–] is the molar concentration of the conjugate base and [HA] is the molar concentration of the weak acid.
- The equation can also be written as: pOH = pKb + log([HB+]/[B]), where [HB+] corresponds to the molar concentration of the conjugate acid and [B] corresponds to the molar concentration of the weak base.
- Lawrence Joseph Henderson first derived the equation to calculate a buffer solution's pH.
- Karl Albert Hasselbalch re-expressed the equation in logarithmic terms.
- Direct methods can easily calculate the ionization constants of strong acids and bases.
- The Henderson-Hasselbalch Equation is used to approximate the pH of weak acid and base solutions.
- It is useful for estimating the pH of a buffer solution and finding the equilibrium pH in acid-base reactions.
- The equation fails to predict accurate values for strong acids and bases because it assumes the concentration of the acid and its conjugate base at chemical equilibrium will remain the same as the formal concentration.
- It fails to offer accurate pH values for extremely dilute buffer solutions as it doesn't consider water's self-dissociation.
- Example: A buffer solution is made from 0.4M CH3COOH and 0.6M CH3COO–, with CH3COOH's acid dissociation constant at 1.8*10-5, its pH is 4.87.
- The Henderson-Hasselbalch equation is valid when it includes equilibrium concentrations of an acid and conjugate base.
- Equilibrium concentrations can differ from those expected by neutralization stoichiometry in solutions containing not-so-weak acids or bases.
- A solid base, like sodium hydroxide or potassium hydroxide, is fully ionic.
- In solution, these compounds dissociate 100% into metal ions and hydroxide ions.
- Each mole of sodium hydroxide that dissolves yields a mole of hydroxide ions in the solution.
- Ka is the acid dissociation constant, and pKa is its negative logarithm.
- Kb is the base dissociation constant, and pKb is its negative logarithm.
- Acid and base dissociation constants are usually expressed in moles per liter (mol / L).
- Chlorine bleach is formed by dissolving chlorine gas in a condensed solution of sodium hydroxide, producing sodium hypochlorite and sodium chloride.
- pH measures the hydrogen ion concentration of an aqueous solution.
- pKa is more precise than pH because it determines what a molecule at a given pH would do.
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