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Fractional Compositions and Concentrations quiz

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  • What happens to the fractional composition of a weak acid solution as pH decreases?
    As pH decreases, the fraction of the acid form increases and the solution becomes more acidic.
  • At what pH are the concentrations of a weak acid and its conjugate base equal?
    The concentrations are equal when pH equals the pKa of the acid.
  • Which equation describes the relationship between pH, pKa, and the ratio of conjugate base to acid?
    The Henderson-Hasselbalch equation: pH = pKa + log([conjugate base]/[acid]).
  • How is the fraction of acid molecules (α) in a monoprotic system calculated?
    It is calculated as [H+]/([H+] + Ka).
  • How is the fraction of conjugate base molecules (α_A-) in a monoprotic system calculated?
    It is calculated as Ka/([H+] + Ka).
  • What is the sum of the fractions of acid and conjugate base forms in a monoprotic system?
    The sum is always 1, representing 100% of the molecules present.
  • How does the fraction of conjugate base change as pH increases in a weak acid solution?
    As pH increases, the fraction of conjugate base increases while the fraction of acid decreases.
  • What are the three possible forms in a diprotic acid system?
    The three forms are the acidic form, the intermediate form, and the basic form.
  • What marks the intersection point between the acid and intermediate forms in a diprotic system?
    The intersection occurs at pH = pKa1, where the concentrations of acid and intermediate forms are equal.
  • What marks the intersection point between the intermediate and basic forms in a diprotic system?
    The intersection occurs at pH = pKa2, where the concentrations of intermediate and basic forms are equal.
  • How is the concentration of the intermediate form in a diprotic system calculated after losing the first acidic hydrogen?
    It is calculated as the concentration of the acid form times Ka1 divided by [H+].
  • How is the concentration of the basic form in a diprotic system calculated after losing both acidic hydrogens?
    It is calculated as the acid form concentration times Ka1 times Ka2 divided by [H+] squared.
  • What happens to the fraction of the basic form in a diprotic system as pH increases?
    The fraction of the basic form increases as pH increases.
  • How can the actual concentrations of acid and conjugate base in a monoprotic system be determined?
    Multiply the fraction of each form by the formal concentration of the solution.
  • What does a graphical representation of fractional composition versus pH show in both mono- and diprotic systems?
    It shows how the proportions of different forms change with pH, with intersections at pKa values where concentrations of forms are equal.