Chem 142, Autumn 2011
Name___________________
Section__________________
Group Activity 3: Molecular Formulas and Chemical Reactions
1. A sample of an organic molecular compound containing C, H, N and O was sent
off for analysis. The first laboratory analyzed a 7.48 mg sample of the compound,
using combustion analysis, and obtained 13.56 mg of CO2 and 3.47 mg H2O. A
second laboratory reported that the compound was 28.85% nitrogen. Determine
the empirical formula.
2. The combustion of solid caffeine (C8H10N4O2) results in the production of gaseous CO2,
H2O, and NO2.
A) Write the balanced reaction for the combustion of caffeine.
B) If 0.0385 moles of caffeine are burned, determine the moles of water that are
formed.
C) If 7.48 grams of caffeine are burned, how many grams of water will be formed?
D) How many moles of molecular oxygen are consumed in order to burn 7.48 grams of
caffeine?
3. DDT (C14H9Cl5) is an insecticide that is harmful to just about everything. It is produced
from the reaction of chlorobenzene (C6H5Cl) with chloral (C2HOCl3) through the
following reaction:
2C6 H5Cl (l )  C2HOCl3 (l ) 
 C14H9Cl5 ( s)  H 2O ( g )
Consider the reaction between 1140 g of chlorobenzene and 485 g of chloral.
A) Identify the limiting reactant.
B) What mass of DDT is formed?
C) Calculate the mass of the non-limiting reactant remaining.
Useful Information
Avogadro’s number: 6.022 x 1023 particles = 1 mol
Atomic Mass Unit (amu) = 1.661 x 10-24 g
1 mg = 0.001 g