CHEM 1411 - Chapter 3
STOICHIOMETRY
1. Balance the following equations:
a) C5H10O2 + O2  CO2 + H2O
b) PCl5 + H2O  H3PO4 + HCl
c) Al(OH)3 + H2SO4  ____________+
d) Na + ________  NaOH + H2
____________
2. Write balanced chemical equations to correspond to each of the following descriptions:
a)
b)
c)
d)
Heptane, C7H16, is burnt in air
When sulfur trioxide gas reacts with water.
Lithium metal is added to water
ZnCO3(s) is decomposed upon heating
3. Determine the formula weights ( Molecular mass) of each of the following compounds:
a) Ca(C2H3O2)2
b) CH3CH2COOH
c) (NH4)3PO4
4. Calculate the percentage composition of elements in the following compounds;
a) Benzoic acid, C7H6O2
b) Urea, (NH2)2CO
c) Laughing gas, N2O
5. Naturally occurring magnesium has the following isotopic abundances:
Isotope
Mg-24
Mg-25
Mg-26
Abundance
78.70%
10.13%
11.17%
Mass
23.98504
24.98584
25.98259
Calculate the average atomic mass of magnesium.
6. Complete the following conversions;
a) Number of moles in 0.005 g water
c) Mass in grams of 2.50 mole O2
b) Number of molecules in 3.50 mole NaOH
d) Number of moles in 10.5 g C6H12O6
7. Determine the empirical formulas of each of the compounds if a sample contains the
following compositions:
a) 62.1% C, 5.21% H, 12.1% N, and 20.7% O
b) 0.104 mol K, 0.052 mol C, and 0.152 mol O
8. Determine the molecular formula of each of the following compounds?
a) Empirical formula HCO2, molar mass = 90.0 g/mol
b) The composition of adipic acid is 49.3% C, 6.9% H, and 43.8% O (by mass). The molar mass
of the compound is about 146 g/mol. Find the Empirical formula and Molecular formula.
9. The complete combustion of octane, C8H18, a component of gasoline, proceeds as
follows:
2 C8H18 + 25 O2  16 CO2 + 18 H2O
a) How many moles of CO2 are produced when 1.50-mol octane reacted?
b) How many grams water produced in this reaction?
c) How many moles oxygen required forming 90.0 g water?
10. In a certain experiment 2.50 g of NH3 reacts with 2.85 g of O2. Identify the limiting reactant? How
many grams of NO form? How much excess of reactant remain after the liming reactant is
completely consumed?
11. Given 30.0 g benzene and 65.0 g bromine in the following reaction:
C6H6 + Br2  C6H5Br + HBr
If the actual yield of C6H5Br, Bromobenzene, is 56.7 g, what is the percentage yield?