This document contains 7 problems related to general chemistry. It provides chemical equations to balance, asks students to calculate formula weights and percent compositions of substances, defines key concepts like moles and molar mass, and has multi-step calculations involving moles, molar mass, and grams. The problems cover topics like stoichiometry, formula weights, percent composition, gas laws, and molar conversions.

1. KEY
GENERAL CHEMISTRY-I (1411)
S.I. # 10
1. Balance the following equations:
a. 6 Li (s) + __1__ N2 (g)  ___2__ Li3N (s)
b. __1 La2O3 (s) + __3__ H2O (l)  ___2__ La(OH)3 (aq)
c. __2 NH4NO3 (s)  __2__ N2 (g) + ___1__ O2 (g) + ___4__ H2O (g)
d. __1 Ca3P2 (s) + __6__ H2O (l)  ___3__ Ca(OH)2 (aq) + ___2__ PH3 (g)
e. __3 Ca(OH)2 (aq) + __2__ H3PO4 (aq) ___1_ Ca3(PO4)2 (s) + _6__ H2O (l)
f. __2 AgNO3 (aq) + __1_Na2SO4 (aq)  ___1__ Ag2SO4 (s) + __2_ NaNO3 (aq)
g. _4 CH3NH2 (g) + _9_O2 (g) _4__ CO2 (g) + __10__ H2O (g) + ___2__ N2 (g)
2. Determine the formula weights (FW) of each of the following:
a. Nitrous Oxide, N2O ____44 amu_____
b. benzoic acid, HC7H5O2 ____122 amu _____
c. Magnesium Hydroxide, Mg(OH)2____58.3 amu _____
d. Urea (NH2)2CO ____60 amu _____
e. isopentyl acetate CH3CO2C5H11 ____130 amu _____
3. Calculate the percent by mass of:
a. carbon in acetylene, C2H2
FW = 26 %C = [(2)(12.0 amu) / (26.0 amu)] x 100 = 92.3%
b. Hydrogen in ascorbic acid HC6H7O6
FW = 176 %H = [(8)(1.0 amu) / (176.0 amu)] x 100 = 4.5%
c. Hydrogen in ammonium sulfate (NH4)2SO4
FW = 132.1 %H = [(8)(1.0 amu) / (132.1 amu)] x 100 = 6.1%
d. Platinum in PtCl2(NH3)2
FW = 300.1 %Pt = [(1)(195.1 amu) / (300.1 amu)] x 100 = 65.01%
e. Oxygen in C18H24O2
FW = 272.0 %O = [(2)(16.0 amu) / (272.0 amu)] x 100 = 11.8%
f. carbon in C18H27NO3
FW = 305.0 %C = [(18)(12.0 amu) / (305.0 amu)] x 100 = 70.8%
4. a. What is Avogadro’s number, and how is it related to the mole? b. What is the
relationship between the formula weight of a substance and its molar mass?
a. 6.022x1023. This is the number of objects in a mole of anything
b. The formula weight of a substance in amu has the same numerical value as the
molar mass expressed in grams.
5. a. what is the mass, in grams, of a mole of 12C? b. How many carbon atoms are

2. KEY
present in a mole of 12C?
a. exactly 12 g b. 6.0221421x1023, Avogadro’s number
6. a. What is the mass, in grams, of 0.0714 mol of iron(III) sulfate?
Fe2(SO4)3 FW=Molar Mass= 399.9 g / mol
0.0714 mol Fe2(SO4)3 x (399.9 g Fe2(SO4)3) = 28.6 g Fe2(SO4)3
1 mol
b. How many moles of ammonium ions are in 8.776 g of ammonium carbonate?
(NH4)2CO3 MM = 96.087 g / mol
8.776 g (NH4)2CO3 x ( 1 mol (NH4)2CO3 )x( 2 mol NH4+) = 0.1827 mol NH4+
(96.087g (NH4)2CO3) (1 mol (NH4)2CO3)
c. What is the mass, in grams, of 6.52x1021 molecules of aspirin, C9H8O4?
C9H8O4 MM=180.2 g / mol
6.52x1021molecules x (1 mol) x (180.2 g C9H8O4)= 1.95 g
(6.022x1023molecules) (1 mol aspirin)
7. A sample of the male sex hormone testosterone, C19H28O2, contains 7.08x1020
atoms of hydrogen. a. How many atoms of carbon does it contain? b. How many
molecules of testosterone does it contain? c. How many moles of testosterone does it
contain? d. What is the mass of this sample in grams?
a. 7.08x1020 H atoms x (19 C atoms) = 4.80x1020 C atoms
(28 H atoms)
b. 7.08x1020 H atoms x (1 C19H28O2 molecule) = 2.53x1019 C19H28O2 molecules
(28 H atoms)
c. 2.529x1019 C19H28O2 molecules x ( 1 mol ) = 4.199x10-5 mol C19H28O2
(6.022x1023 molecules)
d. C19H28O2 MM = 288.4 g / mol
4.199x10-5 mol C19H28O2 x (288.4 g C19H28O2) = 0.0121 g C19H28O2
(1 mol)