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Titrations of Diprotic and Polyprotic Acids quiz

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Terms in this set (15)

  • What is the main difference between monoprotic and diprotic buffers in terms of Ka values?
    Monoprotic buffers have one Ka value, while diprotic buffers have two Ka values because they have two acidic hydrogens.
  • How many major forms does a diprotic acid have, and what are they called?
    A diprotic acid has three major forms: the acidic form (both hydrogens), the intermediate form (one hydrogen lost), and the basic form (both hydrogens lost).
  • When using the Henderson-Hasselbalch equation for buffers, what units can be used for the concentrations?
    You can use either molarity or moles, depending on whether you are given just molarity or both volume and molarity.
  • How do you calculate moles from volume and molarity?
    Multiply the volume in liters by the molarity to get the number of moles.
  • Which Ka value do you use when calculating the pH of a buffer made from the acidic and intermediate forms of a diprotic acid?
    You use Ka1, which corresponds to the removal of the first acidic hydrogen.
  • What is the conjugate base in a buffer made from carbonic acid (H2CO3) and sodium bicarbonate (NaHCO3)?
    The conjugate base is sodium bicarbonate (NaHCO3), which has one less hydrogen than carbonic acid.
  • When calculating the pH of a buffer made from the intermediate and basic forms of a diprotic acid, which Ka value is used?
    Ka2 is used, as it corresponds to the removal of the second acidic hydrogen.
  • How many Ka values does a triprotic acid have, and what does this mean for buffer calculations?
    A triprotic acid has three Ka values, meaning there are three steps of hydrogen removal and four possible forms.
  • What are the four forms of a triprotic acid like phosphoric acid?
    The four forms are: the fully protonated acid, the first intermediate (one hydrogen lost), the second intermediate (two hydrogens lost), and the fully deprotonated base.
  • Which form of a polyprotic acid is always used as the conjugate base in the Henderson-Hasselbalch equation?
    The conjugate base is always the form with one less hydrogen than the weak acid form.
  • What determines which Ka value to use in the Henderson-Hasselbalch equation for polyprotic acids?
    The forms of the acid and base present in the buffer determine which Ka value to use.
  • In a buffer made from potassium dihydrogen phosphate and potassium monohydrogen phosphate, which pKa is used?
    pKa2 is used, as these forms differ by the second hydrogen.
  • Why do calculations become more complicated with diprotic and polyprotic buffers compared to monoprotic buffers?
    Because there are multiple Ka values and more possible forms, you must carefully identify which forms are present to choose the correct Ka.
  • What is the general form of the Henderson-Hasselbalch equation for any buffer?
    pH = pKa + log (conjugate base / weak acid).
  • What should you always identify first when solving buffer problems involving polyprotic acids?
    You should first identify which forms of the acid and base are present to determine which Ka value to use.