CLiC Problem Set #3 Autumn Quarter 2015

Problem 1

In last weeks problem set, we identified a hydrocarbon by combustion analysis. Similarly, begin this question by writing out and balancing the equation for the combustion of the epilepsy drug

phenobarbital, C12H12N2O3. (Note: When combusted in hydrocarbons, nitrogen forms N2). Then,

answer the following questions:

a.) Draw the Lewis dot structures for all products in this reaction, indicating the formal charge for each atom. For each molecule, state or indicate:

(1) Any dipole moments

(2) The steric number of the central atom (if applicable)

(3) The molecular geometry

(4) The overall molecular dipole moment (if applicable)

b.) One possible resonance structure of phenobarbital is given below. Would you expect this form to be stable? Why or why not? If not, give a more stable resonance structure. (Hint: if you are

stuck, try reviewing how calculating formal charges might be of assistance)

Problem 2

Refer to your balanced reaction for the combustion of phenobarbital. If 151g of phenobarbital are

combusted, what volume of gases are produced? You may assume the temperature of all gaseous products is 150 C, at a pressure of 1atm.

Problem 3

While volunteering at a hospital, you spill a tray of portioned-out pills on the counter. Oh no! You

quickly identify most pills by shape and color. However, phenobarbital and aspirin (C9H8O4) are both

white, round, 100mg1 tabletsone type unhelpfully labeled V, the other M. Recalling general chemistry, you quickly devise a way to identify which tablet is which drug. You burn 3 M pills and measure the temperature (150C) and volume (752mL) of gas produced from combustion. Just as you

are finishing up the experiment, your supervisor comes in and angrily asks you what you are doing.

Explain to her how your experiment works, and tell her which pills are which drug.

1 You may assume the tablets are pure and contain no filler agents.