Chapter 3 – Mass Relationships in Chemical Reactions
1. Balance the following equations:
a) C5H10O2 + O2  CO2 + H2O
b) PCl5 + H2O  H3PO4 + HCl
c) Al(OH)3 + H2SO4  ____________+
d) Na + ________  NaOH + H2
Albert Kweyete
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2. Write balanced chemical equations to correspond to each of the following descriptions:
a)
b)
c)
d)
Heptane, C7H16, is combusted in air
When sulfur trioxide gas reacts with water, a solution of sulfuric acid forms
Lithium metal is added to water
ZnCO3(s) is decomposed upon heating
3. Determine the formula weights of each of the following compounds:
a) Ca(C2H3O2)2
b) CH3CH2COOH
c) (NH4)3PO4
4. Calculate the percentage compositions in the following compounds;
a) Benzoic acid, C7H6O2
b) Urea, (NH2)2CO
c) Laughing gas, N2O
5. Gallium (Ga) consists of two naturally occurring isotopes with masses of 68.926 amu and
70.926 amu. Calculate the abundance of each isotope. The average atomic mass of Ga is
69.726 amu.
6. Complete the following conversions;
a) moles of 0.005 g water
c) grams mass of 2.50 mole O2
b) atoms in 3.50 mole NaOH
d) carbon atoms 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
c) 11.66g iron and 5.01g oxygen
8. Determine the molecular formula of each of the following compounds?
a) empirical formula HCO2, molar mass = 90.0 g/mol
b) 75.69% C, 8.80% H, and 15.51% O by mass; molar mass 206g
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9. Combustion analysis of toluene, a common organic solvent, produces 5.86 mg of CO2 and
1.37 mg of H2O. If the compound contains only carbon and hydrogen, what is its
molecular formula? Its molecular mass is 92 g/ mol.
10. A 0.1005 g sample of organic solvent is combusted, producing 0.2829 g of CO2 and
0.1159 g of water. If the compound has a molar mass of 156 g/mol, what is its
molecular formula?
11. 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 to form 90.0 g water?
12. In a certain experiment 2.50 g of NH3 reacts with 2.85 g of O2. Which reactant is the
limiting reactant? How many grams of NO form? How much excess reactant remains
after the liming reactant is completely consumed?
13. 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?
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