PHAR407: Physicochemical Properties of Drug Molecules
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Questions and Answers

What is the purpose of using low pH in weak acid extractions?

  • To extract B but not A-
  • To extract HA and BH+
  • To extract HA but not BH+ (correct)
  • To extract A- and B

    • What is the rate of a chemical reaction?

  • The number of moles transferred from reactant to product in unit time (correct)
  • The time required to complete the reaction
  • The concentration of the reactant
  • The number of moles transferred from product to reactant in unit time

    • What is the differential rate law?

  • A mathematical description of the rate of a reaction based on stoichiometry
  • A graphical representation of the rate of a reaction
  • A theoretical model of the rate of a reaction
  • An experimental determination of the rate of a reaction based on concentrations (correct)

    • What is the characteristic of a zero-order reaction?

    <p>The rate of reaction is constant and independent of concentration of the reactant</p> Signup and view all the answers

    What is the mathematical representation of the rate of decomposition of a zero-order reaction?

    <p>x = kt</p> Signup and view all the answers

    How can the order of a reaction be determined graphically?

    <p>All of the above</p> Signup and view all the answers

    What is the half-life period of a zero-order reaction?

    <p>t1/2 = a / 2k</p> Signup and view all the answers

    What is the characteristic of a first-order reaction?

    <p>The rate of reaction depends on the concentration of the reactant</p> Signup and view all the answers

    How can the order of a reaction be determined numerically?

    <p>By using the initial rate data</p> Signup and view all the answers

    What is the shelf-life period of a zero-order reaction?

    <p>t0.9 = a / 10k</p> Signup and view all the answers

    Study Notes

    Sample Purity and Chemical Separations

    • Many chemical analyses are not specific for one compound and respond to many potential interferences in the sample.
    • It is often necessary to first purify the compound of interest by removing interfering substances before a selective analysis is possible.
    • Techniques available for chemical separations include extraction, distillation, precipitation, chromatography, centrifugation, filtration, and others.

    Liquid-Liquid Extraction or Solvent Extraction

    • Diethyl ether, toluene, and hexane are common solvents that are immiscible with water, less dense than water, and form a separate phase that floats on top of the aqueous phase.
    • Chloroform, dichloromethane, and carbon tetrachloride are common solvents that are denser than water.
    • The distribution coefficient (K) is used to describe the ratio of the concentration of a compound in the organic phase to its concentration in the aqueous phase.
    • Formulae used in extraction:
      • q = fraction of compound remaining in aqueous phase = naq/nt
      • p = fraction of compound extracted to organic phase = norg/nt
      • q + p = 1
      • q and p after single extraction can be determined by the formulae:
        • q = KVR + 1
        • p = 1 / (KVR + 1)
      • % remaining in aqueous phase = qx100
      • % extracted = px100
      • After multiple (n) extractions, the formula: qn = (1 / (KVR + 1))^n is used

    Influence of Ionization on Partitioning

    • The ability to change the distribution ratio of a weak acid or weak base with pH is useful in selecting conditions that will extract some compounds but not others.
    • Use low pH to extract HA but not BH+ (weak acid extractions)
    • Use high pH to extract B but not A- (weak base extractions)

    Chemical Kinetics

    • Chemical kinetics is concerned with the rate of chemical reactions and the mechanism by which they proceed.
    • The rate of chemical reaction (its velocity or speed) is the number of moles transferred from reactant to product in unit time.
    • The rate law shows how the rate of a reaction depends on concentrations of various species in the reaction.
    • The rate constant (k) is a measure of the rate of reaction.

    Orders of Reaction

    • Zero-order reaction: the reaction rate is constant and independent of the concentration of the reactant.
    • First-order reaction: the rate of reaction depends on the concentration of the reactant.
    • Second-order reaction: the rate of reaction depends on the concentration of the reactant squared.
    • Third-order reaction: the rate of reaction depends on the concentration of the reactant cubed.
    • Determination of the order of reaction can be done numerically or graphically.

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    Description

    This quiz covers the introduction to physicochemical properties of drug molecules, specifically sample purity and removal of interfering substances for selective analysis.

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