3. Cocaine is a weak organic base whose molecular formula is C17H21NO4. At 15 oC

Question

3. Cocaine is a weak organic base whose molecular formula is C17H21NO4. At 15 oC an aqueous solution of cocaine was found to have a pH of 8.53 and an osmotic pressure of 52.7 torr. a. b. C. What is the molarity of this solution? What is kb of cocaine? What concentration of NaOH solution would have the same pH as this solution of cocaine? 4. Consider a mixture of 25.0 mL of 0.100 M HCI and 75.0 mL of 0.100 M acetic acid. a. Construct an ICE table b. Determine the pH of the solution 5. Consider the reaction between hydrogen peroxide and iron in acidic solution h1,02(aq) + Fe+ (aq) Fe3+ (aq) + H2O(l) a. b. c. Balance the reaction in acidic solution Determine the standard potential for this reaction Determine the potential for this reaction if the concentrations of hydrogen peroxide, iron (II), and iron (III) are all 0.10 M and the solution is pH = 4

Explanation / Answer

= osmotic pressure = iCRT

van't hoff factor = degree of dissociation

C = osmolarity

R = gas constant

T = temperature in K

= 52.7 torr

1 torr = 133.322 Pa

52.7 torr = 7026.07 Pa

15 oC = 15 + 273 = 288K

7026.07 Pa = iC x 8.314 Pa.m3/mol.K x 288 K

iC = 2.934 osm

pH = 8.53

pOH = 14 - 8.53 = 5.47

Kb = 3.38844 x 10-6

C17H21NO4(aq) <-------------> C17H21NO4H + OH-

A 0 0 initially

A-x x x equilibrium

A-x + x +x = A + x = total osm = iC = 2.934

Kb = x2 / (2.934 - 2x)

=  

Kb = x2/[2.934 - 2x] = 3.38844 x 10-6

2.934 - 2x ~ 2.934

x = 0.00315 M

molarity of cocaine = A = 2.934 - x = 2.931 M

We want OH- = 0.00315 M

molarity of NaOH needed = 0.00315

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