Effect of pH on Drug Solubility Experiment
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Questions and Answers

What is the equilibrium constant K defined by?

  • [H+] / S
  • S = [HA(aq)] + [A-(aq)]
  • [HA(s)] / [HA(aq)]
  • [HA(aq)] / [HA(s)] (correct)

    • What does the equilibrium constant Ka represent in the context of drug solubility?

  • Total concentration of solute
  • Rate of dissociation into ions (correct)
  • Equilibrium between HA(s) and HA(aq)
  • Dissolution rate of the drug

    • What does the equation S=K + KKa /[H+] represent in the context of drug solubility?

  • Concentration of ionic forms
  • Equilibrium between HA(s) and HA(aq)
  • Equilibrium constants K and Ka (correct)
  • Rate of drug solubility

    • What does a plot of S vs 1/[H+] yield in the context of drug solubility?

    <p>A straight line</p> Signup and view all the answers

    What is used to obtain the concentration of A- in the solution?

    <p>Beer-Lambert law</p> Signup and view all the answers

    What is the value of Ɛ in the Beer-Lambert law at a wavelength of 240nm?

    <p>10000 L mol-1 cm-1</p> Signup and view all the answers

    What is the purpose of scratching the side of the flask with a glass rod?

    <p>To encourage recrystallization of phenobarbitone</p> Signup and view all the answers

    What is added to the diluted filtrates for measurement of absorbance?

    <p>pH 10.0 buffer</p> Signup and view all the answers

    How much of each filtrate is accurately pipetted into clean 100mL volumetric flasks?

    <p>10mL</p> Signup and view all the answers

    What must be done if there are any spillages of phenobarbitone?

    <p>Staff must be notified</p> Signup and view all the answers

    What is used to transfer the solid phenobarbitone to a 100 mL conical flask?

    <p>Labelled sample vials</p> Signup and view all the answers

    What is used to make up the volumetric flasks to the line after adding 10mL of each filtrate?

    <p>Water</p> Signup and view all the answers

    What is the equilibrium constant K defined by in the context of drug solubility?

    <p>The concentration of solute in its non-ionic form</p> Signup and view all the answers

    What does the equilibrium constant Ka represent in the context of drug solubility?

    <p>The extent of dissociation of the weakly acidic drug</p> Signup and view all the answers

    What is the equation S=K + KKa /[H+] used to represent in the context of drug solubility?

    <p>The relationship between solubility and pH</p> Signup and view all the answers

    What does a plot of S vs 1/[H+] yield in the context of drug solubility?

    <p>A straight line with gradient KKa and intercept K</p> Signup and view all the answers

    What is the purpose of adding excess base in the form of a pH 10 buffer solution?

    <p>To convert all the dissolved phenobarbitone to A-</p> Signup and view all the answers

    What is the purpose of heating the phenobarbitone and buffer mixture on a hotplate?

    <p>To speed up the dissolution process</p> Signup and view all the answers

    What is the purpose of cooling the mixture in a water bath and thermostat at 25°C?

    <p>To encourage recrystallization of phenobarbitone</p> Signup and view all the answers

    What is the purpose of filtering off the crystals under gravity?

    <p>To separate the phenobarbitone from the buffer solution</p> Signup and view all the answers

    Why are 10mL of each filtrate accurately pipetted into clean 100mL volumetric flasks?

    <p>To make up to the line with water for dilution</p> Signup and view all the answers

    What is the purpose of adding 20mL of pH 10.0 buffer to the diluted filtrates?

    <p>To prepare the samples for absorbance measurement</p> Signup and view all the answers

    What is measured in the experimental method at a wavelength of 240nm?

    <p>The concentration of A- in solution</p> Signup and view all the answers

    What does the equilibrium constant K represent in the context of drug solubility?

    <p>The dissolution of the weakly acidic drug in water</p> Signup and view all the answers

    What is the equation S=K + KKa /[H+] used to represent in the context of drug solubility?

    <p>The solubility of the drug in terms of the total concentration of solute</p> Signup and view all the answers

    What does a plot of S vs 1/[H+] yield in the context of drug solubility?

    <p>A straight line of gradient KKa and intercept K</p> Signup and view all the answers

    What must be done if there are any spillages of phenobarbitone?

    <p>Notify the supervisor and leave the area</p> Signup and view all the answers

    What is the purpose of using a pH 10 buffer solution in the experiment?

    <p>To maintain a constant pH during the experiment</p> Signup and view all the answers

    What does the wavelength of 240nm represent in the experimental method?

    <p>Standard wavelength for Beer-Lambert law</p> Signup and view all the answers

    Why is it important to accurately pipette 10mL of each filtrate into clean 100mL volumetric flasks?

    <p>To ensure a precise concentration for further measurements</p> Signup and view all the answers

    What is the purpose of scratching the side of the flask with a glass rod?

    <p>To enhance crystallization of phenobarbitone</p> Signup and view all the answers

    What is used to transfer the solid phenobarbitone to a 100 mL conical flask?

    <p>Labelled sample vials</p> Signup and view all the answers

    What is the purpose of adding about 50 mL of the appropriate buffer to the solid phenobarbitone?

    <p>To increase the solubility of phenobarbitone</p> Signup and view all the answers

    What does the Beer-Lambert law help obtain in the experiment?

    <p>Concentration of phenobarbitone in solution</p> Signup and view all the answers

    Why must staff be notified of any spillages of phenobarbitone during the experiment?

    <p>To ensure proper safety measures are followed</p> Signup and view all the answers

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