Lab 3 Flashcards
Name 2 uses for the Henderson-Hasselbach Equation
1.Calculating ratio of ionized to unionized species of a molecule when preparing buffer solutions
- To predict absorption, distribution, and excretion properties of a drug
What does pKa determine?
Gives the relative acid strength of a molecule
As pKa decreases, acidity _____
increases
As Ka increases, acidity______
increases
Are drugs in their ionized or nonionized form? Why?
Non ionized because they are lipophilic and will cross the cell membrane
The distribution of a drug can be manipulated by____
changing the pH
If you want a basic drug to be excreted from the body you should ____ the pH of the urine
decrease
What 2 things does solubility depend on?
- Molecular properties of the solute and solvent
- Temperature
What is intrinsic solubility?
Maximum amount of solute that can dissolve in a specified volume of solvent
Water-soluble compounds dissolve in water primarily via which two bonds?
Hydrogen and ionic
For weak acids, ionization _____ with increasing pH
increases
For weak bases, ionization ____ with decreasing pH
increases
Degree of ionization can be calculated using ______
Hendersen-Hasselbach equation
How to find [HA] if using a base??
plug in absorbance value for buffer into the standard curve equation as “y.” solving for x will give [A-]. To find [HA] subtract [A-] from C2
What is the formula for calculating molar extinction coefficient if using an acid?
E = absorbance/ 1cm * [HA]M
How to calculate intrinsic aqueous solubility?
Given intrinsic solubility (mg/mL) * final volume in mL
concentration could be measured in _____ or _____
g/L or mg/mL
How to calculate non intrinsic solubility??
mg solute - mg intrinsic aqueous solubility
How to calculate critical solubilizing pH??
pka + log [insoluble]/[intrinsically soluble]
The formation of a solution in a solute and solvent system is a _____ process
physical
When is a solution considered saturated?
Once the compound reaches maximum solubility
The interactions that determine the solubility of a substance in a liquid depends largely on ______
The ability of the solute to interact and form bonds with the solvent
Name 3 ways supersaturated aqueous solutions can be prepared
Manipulating pH, temperature, and mixing solvents
What 2 terms describe the phenomenon by which excess solute falls out of solution
crystallization and precipitation
What is the difference between solubility and intrinsic solubility?
solubility is defined as the ability of a substance called a solute to interact and form bonds with the solvent and thus physically dissolve in the solvent to form a solution. intrinsic solubility is defined as the MAXIMUM amount of solute that can dissolve in a given amount of solvent at specified temperature and pressure.
The absorbance of a sample solution measured by a Spectrophotometer is 0.65 (pathlength = 1cm). The concentration of the solution is 4 * 10-6 µM. Calculate the molar extinction coefficient (2 decimal places and write unit).
410-6 micromolar = 410-12 molar
0.65=4*10-12x
= 1.6310^11 Lmol^-1*cm^-1
Does pH affect solubility of benzoic acid in water? How does solubility change (increase or decrease) when NaOH is added to the solution of Benzoic acid? Explain
Yes. When NaOH is added to the solution of benzoic acid, the solubility of benzoic acid increases in the solution. Benzoic acid is a weak acid and will readily donate its proton to NaOH (strong base) and become ionized. Ionized benzoic acid is more soluble in a solution because it carries a full charge
The pH of the phosphate buffer is 7. The concentration of the free form of Bromothymol blue (HBTB) is 700 µM and the ionized concentration of bromothymol blue in phosphate buffer is 6 M. Calculate the pKa of bromothymol blue.
pKa= pH- log[ionized]/[not ionized]
7-log[6]/[0.0007]
pka= 7-3.933
pka=3.067
The pKa of benzoic acid is 4.2. The intrinsic aqueous solubility of benzoic acid in 0.05 M NaOH solution is 20.4 and insoluble amount is 10.4. Calculate the critical pH for solubilization of benzoic acid.
pH = pKa + log [A-]/[HA]
pH = pKa + log [insoluble]/[intrinsically soluble]
pH= 4.2 + log[10.4]/[20.4]
pH= 4.2 + -0.292597
pH=3.9
