Skip to main content
Back

Polyprotic Acid quiz

Control buttons has been changed to "navigation" mode.
1/15

Terms in this set (15)

  • What is a triprotic acid and how is it generally represented?
    A triprotic acid is a polyprotic acid with three acidic hydrogens, generally represented as H3A.
  • What does Ka1 represent in the context of a triprotic acid?
    Ka1 is the acid dissociation constant for the loss of the first acidic hydrogen from the triprotic acid.
  • How does the value of Ka1 compare to Ka2 and Ka3 for a triprotic acid?
    Ka1 is always the largest, Ka2 is smaller than Ka1, and Ka3 is the smallest, as it becomes harder to remove each subsequent hydrogen.
  • What is the equilibrium expression for the first dissociation of a triprotic acid?
    The equilibrium expression is [H2A-][H3O+]/[H3A].
  • What is the basic form of a triprotic acid and how is it denoted?
    The basic form is when all acidic hydrogens are removed, denoted as A3-.
  • What does Kb1 represent for a polyprotic base derived from a triprotic acid?
    Kb1 is the base dissociation constant for the acceptance of the first hydrogen ion by the basic form (A3-).
  • How many different forms can a triprotic acid exist in, and what are they?
    A triprotic acid can exist in four forms: the fully acidic form (H3A), two intermediate forms (H2A- and HA2-), and the fully basic form (A3-).
  • How are the Ka and Kb values of a triprotic acid related to Kw?
    Ka1 × Kb3 = Kw, Ka2 × Kb2 = Kw, and Ka3 × Kb1 = Kw, where Kw is the ion product of water.
  • What is the value of Kw at 25°C?
    Kw is 1.0 × 10^-14 at 25°C.
  • When calculating pH for the fully acidic form of a triprotic acid, which constant do you use?
    You use Ka1 to calculate the pH of the fully acidic form (H3A).
  • Which constant is used to calculate pH for the fully basic form of a triprotic acid?
    You use Kb1 to calculate the pH of the fully basic form (A3-).
  • What is the formula to estimate [H+] for the first intermediate form of a triprotic acid?
    [H+] ≈ sqrt((Ka1 × Ka2 × initial concentration) / (Ka1 + initial concentration)).
  • What is the formula to estimate [H+] for the second intermediate form of a triprotic acid?
    [H+] ≈ sqrt((Ka2 × Ka3 × initial concentration) / (Ka2 + initial concentration)).
  • Why do the formulas for [H+] in the intermediate forms use two Ka values?
    Because each intermediate form is between two dissociation steps, so both relevant Ka values are involved in the calculation.
  • How do you calculate pH once you have determined [H+] for any form?
    pH is calculated as the negative logarithm of the hydrogen ion concentration: pH = -log[H+].