Lab 3

Question 1

Name 2 uses for the Henderson-Hasselbach Equation

Answer 1

1.Calculating ratio of ionized to unionized species of a molecule when preparing buffer solutions

2. To predict absorption, distribution, and excretion properties of a drug

Question 2

What does pKa determine?

Answer 2

Gives the relative acid strength of a molecule

Question 3

As pKa decreases, acidity _____

Answer 3

increases

Question 4

As Ka increases, acidity______

Answer 4

increases

Question 5

Are drugs in their ionized or nonionized form? Why?

Answer 5

Non ionized because they are lipophilic and will cross the cell membrane

Question 6

The distribution of a drug can be manipulated by____

Answer 6

changing the pH

Question 7

If you want a basic drug to be excreted from the body you should ____ the pH of the urine

Answer 7

decrease

Question 8

What 2 things does solubility depend on?

Answer 8

1. Molecular properties of the solute and solvent
2. Temperature

Question 9

What is intrinsic solubility?

Answer 9

Maximum amount of solute that can dissolve in a specified volume of solvent

Question 10

Water-soluble compounds dissolve in water primarily via which two bonds?

Answer 10

Hydrogen and ionic

Question 11

For weak acids, ionization _____ with increasing pH

Answer 11

increases

Question 12

For weak bases, ionization ____ with decreasing pH

Answer 12

increases

Question 13

Degree of ionization can be calculated using ______

Answer 13

Hendersen-Hasselbach equation

Question 14

How to find [HA] if using a base??

Answer 14

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

Question 15

What is the formula for calculating molar extinction coefficient if using an acid?

Answer 15

E = absorbance/ 1cm * [HA]M

Question 16

How to calculate intrinsic aqueous solubility?

Answer 16

Given intrinsic solubility (mg/mL) * final volume in mL

Question 17

concentration could be measured in _____ or _____

Answer 17

g/L or mg/mL

Question 18

How to calculate non intrinsic solubility??

Answer 18

mg solute - mg intrinsic aqueous solubility

Question 19

How to calculate critical solubilizing pH??

Answer 19

pka + log [insoluble]/[intrinsically soluble]

Question 20

The formation of a solution in a solute and solvent system is a _____ process

Answer 20

physical

Question 21

When is a solution considered saturated?

Answer 21

Once the compound reaches maximum solubility

Question 22

The interactions that determine the solubility of a substance in a liquid depends largely on ______

Answer 22

The ability of the solute to interact and form bonds with the solvent

Question 23

Name 3 ways supersaturated aqueous solutions can be prepared

Answer 23

Manipulating pH, temperature, and mixing solvents

Question 24

What 2 terms describe the phenomenon by which excess solute falls out of solution

Answer 24

crystallization and precipitation

Question 25

What is the difference between solubility and intrinsic solubility?

Answer 25

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.

Question 26

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).

Answer 26

410-6 micromolar = 410-12 molar

0.65=4*10-12x

= 1.6310^11 Lmol^-1*cm^-1

Question 27

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

Answer 27

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

Question 28

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.

Answer 28

pKa= pH- log[ionized]/[not ionized]

7-log[6]/[0.0007]
pka= 7-3.933
pka=3.067

Question 29

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]

Answer 29

pH= 4.2 + log[10.4]/[20.4]

pH= 4.2 + -0.292597

pH=3.9