Practice for Mass Spec, Gram-Mole-Particle, Empirical and Molecular Formulas
43. The mass spectrum of bromine (Br2) consists of three peaks with the following
characteristics:
Mass (amu)
157.84
159.84
161.84
Relative size
0.2534
0.5000
0.2466
44. The stable isotopes of iron are 54Fe, 56Fe, 57Fe and 58Fe. The mass spectrum of
iron is below. Use the data on the mass spectrum to estimate the average atomic mass
of iron and compare it to the value given on the periodic table.
72. Dimethylnitrosamine, (CH3)2N2O, is a carcinogenic substance that may be formed in
foods, beverages or gastric juices from the reaction of nitrite ion (a food preservative)
with other substances.
a. What is the molar mass of dimethylnitrosamine?
b. How many moles of (CH3)2N2O molecules are present in 250 mg of
dimethylnitrosamine?
c. What is the mass of 0.050 mole of dimethylnitrosamine?
d. How many atoms of hydrogen are in 1.0 mole of dimethylnitrosamine?
e. What is the mass of 1.0 x 106 molecules of dimethylnitrosamine?
f. What is the mass in grams of one molecule of dimethylnitrosamine?
76. Arrange the following substances in order of increasing mass percent of carbon.
a. caffeine, C8H10N4O2
b. sucrose, C12H22O11
c. ethanol, C2H5OH
86. A sample of urea contains 1.121g N, 0.161g H, 0.480g C and 0.640g O. What is
the empirical formula of urea?
88. Determine the molecular formula of a compound that contains 26.7% P, 12.1%N
and 61.2% Cl and has a molar mass of 580g/mol.