# 8.E: Exercises

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#### 8.3:  Stoichiometry and the Molar Interpretation

1. What are all the conversion factors that can be constructed from the balanced chemical reaction:  2 S(s) + 3 O2(g) → 2 SO3(g)?

$$\dfrac{2\;\mathrm{mol}\;{\mathrm S}}{3\;\mathrm{mol}\;{\mathrm O}_2}$$; $$\dfrac{3\;\mathrm{mol}\;{\mathrm O}_2}{2\;\mathrm{mol}\;{\mathrm S}}$$; $$\dfrac{1\;\mathrm{mol}\;{\mathrm S}}{1\;\mathrm{mol}\;{\mathrm S}{\mathrm O}_3}$$; $$\dfrac{1\;\mathrm{mol}\;{\mathrm S}{\mathrm O}_3}{1\;\mathrm{mol}\;{\mathrm S}}$$; $$\dfrac{3\;\mathrm{mol}\;{\mathrm O}_2}{2\;\mathrm{mol}\;{\mathrm S}{\mathrm O}_3}$$; $$\dfrac{2\;\mathrm{mol}\;{\mathrm S}{\mathrm O}_3}{3\;\mathrm{mol}\;{\mathrm O}_2}$$

1. Construct the three independent conversion factors possible for these two reactions:
1. 2 H2 + O2 → 2 H2O
2. H2 + O2 → H2O2

Why are the ratios between H2 and O2 different?

The conversion factors are different because the stoichiometries of the balanced chemical reactions are different.

#### 8.4:  Molar Ratios and Mole-to-Mole Conversions

1. Given the chemical equation:  Na(s) + H2O(l) → NaOH(aq) + H2(g)
1. Balance the equation.
2. How many moles of H2 are produced when 332 moles of Na react?
1. 2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g)
2. 166 mol H2

1. Given the chemical equation:  S(s) + O2(g) → SO3(g)
1. Balance the equation.
2. How many moles of O2 are needed when 38 moles of S react?
1. 2 S(s) + 3 O2(g) → 2 SO3(g)
2. 57 mol O2

1. For the balanced chemical equation:

6 H+(aq) + 2 MnO4(aq) + 5 H2O2(l) → 2 Mn2+(aq) + 5 O2(g) + 8 H2O(l)

how many moles of H2O are produced when 75 moles of H2O2 react?

120 mol H2O

1. For the balanced chemical reaction:

2 C6H6(l) + 15 O2(g) → 12 CO2(g) + 6 H2O(l)

how many moles of CO2 are produced when 56 moles of C6H6 react?

3.4 × 102 mol CO2

1. For the balanced chemical equation:

Fe2O3 + 3 SO3 → Fe2(SO4)3

suppose we need to make 145 moles of Fe2(SO4)3. How many moles of SO3 do we need?

435 mol SO3

1. One way to make sulfur hexafluoride is to react thioformaldehyde, CH2S, with elemental fluorine:

CH2S + 6 F2 → CF4 + 2 HF + SF6

If 45.8 moles of SF6 are needed, how many moles of F2 are required?

275 mol F2

1. For the balanced chemical equation:

3 Cu(s) + 2 NO3(aq) + 8 H+(aq) → 3 Cu2+(aq) + 4 H2O(l) + 2 NO(g)

how many moles of Cu2+ are formed when 55.7 mol of H+ are reacted?

20.9 mol Cu2+

1. For the balanced chemical equation:

Al(s) + 3 Ag+(aq) → Al3+(aq) + 3 Ag(s)

how many moles of Ag are produced when 0.661 mol of Al are reacted?

1.98 mol Ag

1. For the balanced chemical reaction:

4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(l)

how many moles of H2O are produced when 0.669 mol of NH3 react?

1.00 mol H2O

1. For the balanced chemical reaction:

4 NaOH(aq) + 2 S(s) + 3 O2(g) → 2 Na2SO4(aq) + 2 H2O(l)

how many moles of Na2SO4 are formed when 1.22 mol of O2 react?

0.813 mol Na2SO4

1. For the balanced chemical reaction:

4 KO2(s) + 2 CO2(g) → 2 K2CO3(s) + 3 O2(g)

determine the number of moles of both products formed when 6.88 mol of KO2 react.

3.44 mol K2CO3; 5.16 mol O2

1. For the balanced chemical reaction
2 AlCl3 + 3 H2O → Al2O3 + 6 HCl

determine the number of moles of both products formed when 0.0552 mol of AlCl3 react.

0.0276 mol Al2O3; 0.166 mol HCl

#### 8.5:  Mass-to-Mass Conversions

1. What mass of CO2 is produced by the combustion of 1.00 mol of CH4?

CH4(g) + 2 O2(g) → CO2(g) +  2H2O(l)

44.0 g CO2

1. What mass of H2O is produced by the combustion of 1.00 mol of CH4?

CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)

36.0 g H2O

1. What mass of HgO is required to produce 0.692 mol of O2?

2 HgO(s) → 2 Hg(l) + O2(g)

3.00 × 102 g HgO

1. What mass of NaHCO3 is needed to produce 2.659 mol of CO2?

2 NaHCO3(s) → Na2CO3(s) + H2O(l) + CO2(g)

446.8 g NaHCO3

1. How many moles of Al can be produced from 10.87 g of Ag?

Al(NO3)3(aq)+ 3 Ag(s) → Al(s) + 3 AgNO3(aq)

0.03359 mol Al

1. How many moles of HCl can be produced from 0.226 g of SOCl2?

SOCl2(l) + H2O(l) → SO2(g) + 2 HCl(g)

3.80 × 10−3 mol HCl

1. How many moles of O2 are needed to prepare 1.00 g of Ca(NO3)2?

Ca(s) + N2(g) + 3 O2(g) → Ca(NO3)2(s)

0.0183 mol O2

1. How many moles of C2H5OH are needed to generate 106.7 g of H2O?

C2H5OH(l) + 3 O2(g) → 2 CO2(g) + 3 H2O(l)

1.974 mol C2H5OH

1. What mass of O2 can be generated by the decomposition of 100.0 g of NaClO3?

2 NaClO3(s) → 2 NaCl(s) + 3 O2(g)

45.10 g O2

1. What mass of Li2O is needed to react with 1,060 g of CO2?

Li2O(aq) + CO2(g) → Li2CO3(aq)

7.20 × 102 g Li2O

1. What mass of Fe2O3 must be reacted to generate 324 g of Al2O3?

Fe2O3(s) + 2 Al(s) → 2 Fe(s) + Al2O3(s)

507 g Fe2O3

1. What mass of Fe is generated when 100.0 g of Al are reacted?

Fe2O3(s) + 2 Al(s) → 2 Fe(s) + Al2O3(s)

207.0 g Fe

1. What mass of MnO2 is produced when 445 g of H2O are reacted?

H2O(l) + 2 MnO4(aq) + Br(aq) → BrO3(aq) + 2 MnO2(s) + 2 OH(aq)

4290 g MnO2

1. What mass of PbSO4 is produced when 29.6 g of H2SO4 are reacted?

Pb(s) + PbO2(s) + 2 H2SO4(aq) → 2 PbSO4(s) + 2 H2O(l)

91.5 g PbSO4

1. If 83.9 g of ZnO are formed, what mass of Mn2O3 is formed with it?

Zn(s) + 2 MnO2(s) → ZnO(s) + Mn2O3(s)

163 g Mn2O3

1. If 14.7 g of NO2 are reacted, what mass of H2O is reacted with it?

3 NO2(g) + H2O(l) → 2 HNO3(aq) + NO(g)

1.92 g H2O

1. If 88.4 g of CH2S are reacted, what mass of HF is produced?

CH2S + 6 F2 → CF4 + 2 HF + SF6

76.7 g HF

1. If 100.0 g of Cl2 are needed, what mass of NaOCl must be reacted?

NaOCl + HCl → NaOH + Cl2

105.0 g NaOCl

1. Calculate the mass of each product when 100.0 g of CuCl react according to the reaction

2 CuCl(aq) → CuCl2(aq) + Cu(s)

What do you notice about the sum of the masses of the products? What concept is being illustrated here?

67.90 g CuCl2; 32.10 g Cu; the sum is 100.0 g; this agrees with the Law of Conservation of Mass

1. Calculate the mass of each product when 500.0 g of SnCl2 react according to the reaction

2 SnCl2(aq) → SnCl4(aq) + Sn(s)

What do you notice about the sum of the masses of the products? What concept is being illustrated here?

343.5 g SnCl4; 156.5 g Sn; the sum is 500.0 g; this agrees with the Law of Conservation of Mass

1. Write the balanced equation and then determine the number of moles and the mass of chlorine, Cl2, required to react with 10.0 g of sodium metal, Na, to produce sodium chloride, NaCl.

2 Na + Cl2 → 2 NaCl; 0.217 mol Cl2; 15.4 g Cl2

1. Write the balanced equation and then determine the number of moles and the mass of oxygen formed by the decomposition of 1.252 g of mercury(II) oxide.

2 HgO → 2 Hg + O2; 2.851 × 10−3 mol O2; 0.09122 g O2

1. Write the balanced equation and then determine the number of moles and the mass of sodium nitrate, NaNO3, required to produce 128 g of oxygen. (NaNO2 is the other product.)

2 NaNO3 → O2 + 2 NaNO2; 8.00 mol NaNO3; 6.80 × 102 g NaNO3

1. Write the balanced equation and then determine the number of moles and the mass of carbon dioxide formed by the combustion of 20.0 g of carbon in an excess of oxygen.

C + O2 → CO2; 1.67 mol CO2; 73.3 g CO2

1. Write the balanced equation and then determine the number of moles and the mass of Mg required to react with 5.00 g of HCl and produce MgCl2 and H2.

Mg + 2 HCl → MgCl2 + H2; 0.0686 mol Mg; 1.67 g Mg

1. Write the balanced equation and then determine the number of moles and the mass of oxygen formed by the decomposition of 1.252 g of silver(I) oxide.

2 Ag2→ O2 + 4 Ag; 2.902 × 10−3 mol O2; 0.09285 g O2

1. Write the balanced equation and then determine the number of moles and the mass of water formed by the combustion of 20.0 g of acetylene, C2H2, in an excess of oxygen.

2 C2H2 + 5 O2 → 4 CO2 + 2 H2O; 0.768 g H2O; 13.8 g H2O

1. Write the balanced equation and then determine the number of moles and the mass of barium peroxide, BaO2, needed to produce 2.500 g of barium oxide, BaO (O2 is the other product.)

2 BaO2 → 2 BaO + O2; 0.01630 mol BaO2; 2.761 g BaO2

1. I2 is produced by the reaction of 0.4235 mol of CuCl2 according to the following equation:  2 CuCl2 + 4 KI → 2 CuI + 4 KCl + I2
1. How many moles of I2 are produced?
2. What mass of I2 is produced?
1. 0.2118 mol I2
2. 53.74 g I2

1. Silver is often extracted from ores as K[Ag(CN)2] and then recovered by the reaction:  2 K[Ag(CN)2] + Zn → 2 Ag + Zn(CN)2 + 2 KCN
1. How many moles of Zn(CN)2 are produced by the reaction of 35.27 g of K[Ag(CN)2]?
2. What mass of Zn(CN)2 is produced?
1. 0.08861 mol Zn(CN)2
2. 10.41 g Zn(CN)2

#### 8.6:  Limiting Reactants and Excess Reactants

1. Given the statement “20.0 g of methane is burned in excess oxygen,” is it obvious which reactant is the limiting reactant?

Yes. If oxygen is in excess, the methane must be the limiting reactant.

1. Given the statement “the metal is heated in the presence of excess hydrogen,” is it obvious which substance is the limiting reactant despite not specifying any quantity of reactant?

Yes. If the hydrogen is in excess, the metal must be the limiting reactant.

1. Acetylene (C2H2) is formed by reacting 7.08 g of C and 4.92 g of H2.

2 C(s) + H2(g) → C2H2(g)

What is the limiting reactant? How many grams of C2H2 are produced?

Limiting reactant = C; 7.67 g C2H2

1. Ethane (C2H6) is formed by reacting 7.08 g of C and 4.92 g of H2.

2 C(s) + 3 H2(g) → C2H6(g)

What is the limiting reactant? How many grams of C2H6 are produced?

Limiting reactant = C; 8.86 g C2H6

1. If 35.6 g of P4O6 is reacted with 4.77 g of H2O, what is the limiting reactant, and what mass of H3PO3 is produced?

P4O6(s) + 6 H2O(l→ 4 H3PO3(aq)

Limiting reactant = H2O; 14.5 g H3PO3

1. If 377 g of NO2 is reacted with 244 g of H2O, what is the limiting reactant, and how many grams of HNO3 and NO are produced?

3 NO2(g) + H2O(l 2 HNO3(aq) + NO(g)

Limiting reactant = NO2; 344 g HNO3 and 82.0 g NO

1. To form the precipitate PbCl2, 2.88 g of NaCl and 7.21 g of Pb(NO3)2 are mixed in solution. How much precipitate is formed? How much of which reactant is in excess?

2 NaCl(aq) + Pb(NO3)2(aq→ PbCl2(s) + 2 NaNO3(aq)

6.06 g PbCl2 formed; 0.34 g excess NaCl

1. In a neutralization reaction, 18.06 g of KOH are reacted with 13.43 g of HNO3. What mass of H2O is produced, and what mass of which reactant is in excess?

KOH(aq) + HNO3(aq→ KNO3(aq) + H2O(l)

3.839 g H2O formed; 6.10 g excess KOH

1. What is the limiting reactant in a reaction that produces sodium chloride from 8 g of sodium and 8 g of diatomic chlorine?

2 Na(s) + Cl2(g→ 2 NaCl(s)

Cl2

1. What is the limiting reactant when 30.0 g of propane, C3H8, is burned with 75.0 g of oxygen.

C3H8(g) + 5 O2(g→ 3 CO2(g) + 4 H2O(g)

O2

1. What is the limiting reactant when 0.50 g of Cr and 0.75 g of H3PO4 react according to the following chemical equation?

2 Cr(s) + 2 H3PO4(aq→ 2 CrPO4(s) + 3 H2(g)

H3PO4

1. What is the limiting reactant when 1.50 g of lithium and 1.50 g of nitrogen combine to form lithium nitride, a component of advanced batteries, according to the following unbalanced equation?

Li + N2 → Li3N

Li

#### 8.7:  Theoretical Yield and Percent Yield

1. What is the difference between the theoretical yield and the actual yield?

Theoretical yield is what you expect stoichiometrically from a chemical reaction; actual yield is what you actually get from a chemical reaction.

1. What is the difference between the actual yield and the percent yield?

Actual yield is the measured amount of product obtained from a chemical reaction; percent yield is the ratio of the actual yield to the amount predicted from stoichiometry.

1. A worker isolates 2.675 g of SiF4 after reacting 2.339 g of SiO2 with HF. What are the theoretical yield and the actual yield?

SiO2(s) + 4 HF(g) → SiF4(g) + 2 H2O(l)

Theoretical yield = 4.052 g; actual yield = 2.675 g

1. A worker synthesizes aspirin, C9H8O4, according to this chemical equation. If 12.66 g of C7H6O3 are reacted and 12.03 g of aspirin are isolated, what are the theoretical yield and the actual yield?

C7H6O3 + C4H6O3 → C9H8O4 + HC2H3O2

Theoretical yield = 16.51 g; actual yield = 12.03 g

1. A chemist decomposes 1.006 g of NaHCO3 and obtains 0.0334 g of Na2CO3. What are the theoretical yield and the actual yield?

2 NaHCO3(s) → Na2CO3(s) + H2O(l) + CO2(g)

Theoretical yield = 0.6346 g; actual yield = 0.0334 g

1. A chemist combusts a 3.009 g sample of C5H12 and obtains 3.774 g of H2O. What are the theoretical yield and the actual yield?

C5H12(l) + 8 O2(g) → 5 CO2(g)+ 6 H2O(l)

Theoretical yield = 4.508 g; actual yield = 3.774 g

1. What is the percent yield in Exercise 59?

66.02%

1. What is the percent yield in Exercise 60?

72.86%

1. What is the percent yield in Exercise 61?

5.26%

1. What is the percent yield in Exercise 62?

83.72%

1. A student isolated 25 g of a compound following a procedure that would theoretically yield 81 g. What was his percent yield?

31%

1. A sample of 0.53 g of carbon dioxide was obtained by heating 1.31 g of calcium carbonate. What is the percent yield for this reaction?

CaCO3(s→ CaO(s) + CO2(g)

91%

1. The phosphorus pentoxide used to produce phosphoric acid for cola soft drinks is prepared by burning phosphorus in oxygen.
1. What is the limiting reactant when 0.200 mol of P4 and 0.200 mol of O2 react according to the reaction:  P4 + 5 O2 → P4O10?
2. Calculate the percent yield if 10.0 g of P4O10 is isolated from the reaction.
1. O2
2. 87.7%

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