06/30/16
CHEM 1A Quiz 3 (30 points)
ANSWER KEY
Name _________________________________
1. (6 points) Hydrazine is compound made up of molecules built of nitrogen and hydrogen atoms as
follows:
(a) Fill the blanks.
Molecular formula of hydrazine
N 2 H4
Empirical formula hydrazine
NH2
(b) Fill the blanks.
Numeric Value:
Unit:
Molecular weight of hydrazine
32.05
amu
Molar mass of hydrazine
32.05
g
5.32×10−23
g
Average mass of hydrazine
molecules in grams
2. (6 points) Fill the blanks in the following table.
Bromine
Diamond
Sodium
chloride
The number of molecules in 1.00 mole
6.02×1023
none
none
The number of atoms in 1.00 mole
1.20×1024
6.02×1023
1.20×1024
The number of elements in 1.00 mole
1
1
2
The number of substances in 1.00 mole
1
1
1
The number of compounds in 1.00 mole
none
none
1
The mass in grams of 1.00 mole
159.8
12.01
58.44
The volume in cm3 of 1.00 mole
51.5
3.41
26.9
PLEASE TURN OVER!!!
3. (8 points) In a chemical atomic mass determination, the tin content in 3.7692 g of tin
tetrachloride was found to be 1.7170 g. If the atomic weight of chlorine is taken as 35.453 amu,
what is the value for the atomic weight of the tin isolated during this experiment?
mass of Cl = 3.7692 g − 1.7170 g = 2.0522 g
moles of Cl = 2.0522 g / (35.453 g/mol) = 0.057885 mol
moles of Sn = 0.057885 mol / 4 = 0.014471 mol
molar mass of Sn = 1.7170 g / (0.014471 mol) = 118.65 g/mol
A.W. of Sn = 118.65 amu
4. (10 points) 0.487 grams of an organic compound (molar mass is approximately 320 g/mol)
is combusted and found to produce 1.321 g CO2, 0.325 g H2O and 0.0421 g N2. Determine
the empirical and molecular formulas of the compound.
1.321 g CO2
1 mol CO2
×
44.01 g CO2
1 mol H2O
0.325 g H2O ×
0.0421 g N2
18.01 g H2O
=
×
×
1 mol C
1 mol CO2
2 mol H
1 mol H2O
×
×
12.01 g C
= 0.360 g C
1 mol C
1.008 g H
1 mol H
= 0.03638 g
H
0.0421 g N
mass of O = 0.487 g − 0.360 g − 0.03638 g − 0.0421 g = 0.04852 g
C
0.360 g
×
H 0.03638 g
×
O 0.04852 g
×
N
×
0.0421 g
1 mol
12.01 g
1 mol
1.008 g
1 mol
16.00 g
1 mol
14.01 g
= 0.02998 mol
= 0.03609 mol
= 0.003033 mol
= 0.003005 mol
0.02998 mol
0.003005
0.03609 mol
0.003005
0.003033 mol
0.003005
0.003005 mol
0.003005
= 9.976 mol
≈ 10 mol
= 12.01 mol
≈ 12 mol
= 1.01 mol
≈ 1 mol
= 1.00 mol
≈ 1 mol
Molar Mass from Empirical Formula = 162 g/mol
Molecular Formula: (C10H12NO)n
n = (320 g/mol) / (162 g/mol) ≈ 2
C20H24N2O2