35 Questions
What is the equilibrium constant K defined by?
[HA(aq)] / [HA(s)]
What does the equilibrium constant Ka represent in the context of drug solubility?
Rate of dissociation into ions
What does the equation S=K + KKa /[H+] represent in the context of drug solubility?
Equilibrium constants K and Ka
What does a plot of S vs 1/[H+] yield in the context of drug solubility?
A straight line
What is used to obtain the concentration of A- in the solution?
Beer-Lambert law
What is the value of Ɛ in the Beer-Lambert law at a wavelength of 240nm?
10000 L mol-1 cm-1
What is the purpose of scratching the side of the flask with a glass rod?
To encourage recrystallization of phenobarbitone
What is added to the diluted filtrates for measurement of absorbance?
pH 10.0 buffer
How much of each filtrate is accurately pipetted into clean 100mL volumetric flasks?
10mL
What must be done if there are any spillages of phenobarbitone?
Staff must be notified
What is used to transfer the solid phenobarbitone to a 100 mL conical flask?
Labelled sample vials
What is used to make up the volumetric flasks to the line after adding 10mL of each filtrate?
Water
What is the equilibrium constant K defined by in the context of drug solubility?
The concentration of solute in its non-ionic form
What does the equilibrium constant Ka represent in the context of drug solubility?
The extent of dissociation of the weakly acidic drug
What is the equation S=K + KKa /[H+] used to represent in the context of drug solubility?
The relationship between solubility and pH
What does a plot of S vs 1/[H+] yield in the context of drug solubility?
A straight line with gradient KKa and intercept K
What is the purpose of adding excess base in the form of a pH 10 buffer solution?
To convert all the dissolved phenobarbitone to A-
What is the purpose of heating the phenobarbitone and buffer mixture on a hotplate?
To speed up the dissolution process
What is the purpose of cooling the mixture in a water bath and thermostat at 25°C?
To encourage recrystallization of phenobarbitone
What is the purpose of filtering off the crystals under gravity?
To separate the phenobarbitone from the buffer solution
Why are 10mL of each filtrate accurately pipetted into clean 100mL volumetric flasks?
To make up to the line with water for dilution
What is the purpose of adding 20mL of pH 10.0 buffer to the diluted filtrates?
To prepare the samples for absorbance measurement
What is measured in the experimental method at a wavelength of 240nm?
The concentration of A- in solution
What does the equilibrium constant K represent in the context of drug solubility?
The dissolution of the weakly acidic drug in water
What is the equation S=K + KKa /[H+] used to represent in the context of drug solubility?
The solubility of the drug in terms of the total concentration of solute
What does a plot of S vs 1/[H+] yield in the context of drug solubility?
A straight line of gradient KKa and intercept K
What must be done if there are any spillages of phenobarbitone?
Notify the supervisor and leave the area
What is the purpose of using a pH 10 buffer solution in the experiment?
To maintain a constant pH during the experiment
What does the wavelength of 240nm represent in the experimental method?
Standard wavelength for Beer-Lambert law
Why is it important to accurately pipette 10mL of each filtrate into clean 100mL volumetric flasks?
To ensure a precise concentration for further measurements
What is the purpose of scratching the side of the flask with a glass rod?
To enhance crystallization of phenobarbitone
What is used to transfer the solid phenobarbitone to a 100 mL conical flask?
Labelled sample vials
What is the purpose of adding about 50 mL of the appropriate buffer to the solid phenobarbitone?
To increase the solubility of phenobarbitone
What does the Beer-Lambert law help obtain in the experiment?
Concentration of phenobarbitone in solution
Why must staff be notified of any spillages of phenobarbitone during the experiment?
To ensure proper safety measures are followed
Test your knowledge about the influence of pH on the aqueous solubility of weakly acidic drugs with this quiz. Explore the concepts of solubility, equilibrium constants, and the impact of pH on drug solubility.
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