# 3.E: Exercises

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## 3.1: Chemical Equations

### Conceptual Problems

1. How does a balanced chemical equation agree with the law of definite proportions?
2. What is the difference between S8 and 8S? Use this example to explain why subscripts in a formula must not be changed.
3. What factors determine whether a chemical equation is balanced?
4. What information can be obtained from a balanced chemical equation? Does a balanced chemical equation give information about the rate of a reaction?

### Numerical Problems

1. Balance each chemical equation.

a. KI(aq) + Br2(l) → KBr(aq) + I2(s)

b. MnO2(s) + HCl(aq) → MnCl2(aq) + Cl2(g) + H2O(l)

c. Na2O(s) + H2O(l) → NaOH(aq)

d. Cu(s) + AgNO3(aq) → Cu(NO3)2(aq) + Ag(s)

e. SO2(g) + H2O(l) → H2SO3(aq)

f. S2Cl2(l) + NH3(l) → S4N4(s) + S8(s) + NH4Cl(s)

2. Balance each chemical equation.

a. Be(s) + O2(g) → BeO(s)

b. N2O3(g) + H2O(l) → HNO2(aq)

c. Na(s) + H2O(l) → NaOH(aq) + H2(g)

d. CaO(s) + HCl(aq) → CaCl2(aq) + H2O(l)

e. CH3NH2(g) + O2(g) → H2O(g) + CO2(g) + N2(g)

f. Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)

3. Balance each chemical equation.

a. N2O5(g) → NO2(g) + O2(g)

b. NaNO3(s) → NaNO2(s) + O2(g)

c. Al(s) + NH4NO3(s) → N2(g) + H2O(l) + Al2O3(s)

d. C3H5N3O9(l) → CO2(g) + N2(g) + H2O(g) + O2(g)

e. reaction of butane with excess oxygen

f. IO2F(s) + BrF3(l) → IF5(l) + Br2(l) + O2(g)

4. Balance each chemical equation.

a. H2S(g) + O2(g) → H2O(l) + S8(s)

b. KCl(aq) + HNO3(aq) + O2(g) → KNO3(aq) + Cl2(g) + H2O(l)

c. NH3(g) + O2(g) → NO(g) + H2O(g)

d. CH4(g) + O2(g) → CO(g) + H2(g)

e. NaF(aq) + Th(NO3)4(aq) → NaNO3(aq) + ThF4(s)

f. Ca5(PO4)3F(s) + H2SO4(aq) + H2O(l) → H3PO4(aq) + CaSO4•2H2O(s) + HF(aq)

5. Balance each chemical equation.

a. NaCl(aq) + H2SO4(aq) → Na2SO4(aq) + HCl(g)

b. K(s) + H2O(l) → KOH(aq) + H2(g)

c. reaction of octane with excess oxygen

d. S8(s) + Cl2(g) → S2Cl2(l)

e. CH3OH(l) + I2(s) + P4(s) → CH3I(l) + H3PO4(aq) + H2O(l)

f. (CH3)3Al(s) + H2O(l) → CH4(g) + Al(OH)3(s)

6. Write a balanced chemical equation for each reaction.

a. Aluminum reacts with bromine.

b. Sodium reacts with chlorine.

c. Aluminum hydroxide and acetic acid react to produce aluminum acetate and water.

d. Ammonia and oxygen react to produce nitrogen monoxide and water.

e. Nitrogen and hydrogen react at elevated temperature and pressure to produce ammonia.

f. An aqueous solution of barium chloride reacts with a solution of sodium sulfate.

7. Write a balanced chemical equation for each reaction.

a. Magnesium burns in oxygen.

b. Carbon dioxide and sodium oxide react to produce sodium carbonate.

c. Aluminum reacts with hydrochloric acid.

d. An aqueous solution of silver nitrate reacts with a solution of potassium chloride.

e. Methane burns in oxygen.

f. Sodium nitrate and sulfuric acid react to produce sodium sulfate and nitric acid.

## 3.3: Formula Masses

### Conceptual Problems

1. What is the relationship between an empirical formula and a molecular formula
2. Construct a flowchart showing how you would determine the empirical formula of a compound from its percent composition.

### Numerical Problems

Please be sure you are familiar with the topics discussed in Essential Skills 2 (Section 3.7 "Essential Skills 2") before proceeding to the Numerical Problems.

a. What is the formula mass of each species?

a. ammonium chloride

b. sodium cyanide

c. magnesium hydroxide

d. calcium phosphate

e. lithium carbonate

f. hydrogen sulfite ion

b. What is the molecular or formula mass of each compound?

a. potassium permanganate

b. sodium sulfate

c. hydrogen cyanide

d. potassium thiocyanate

e. ammonium oxalate

f. lithium acetate

1. What is the mass percentage of water in each hydrate?

a. H3AsO4·0·5H2O

b. NH4NiCl3·6H2O

c. Al(NO3)3·9H2O

2. What is the mass percentage of water in each hydrate?

a. CaSO4·2H2O

b. Fe(NO3)3·9H2O

c. (NH4)3ZrOH(CO3)3·2H2O

3. Which of the following has the greatest mass percentage of oxygen—KMnO4, K2Cr2O7, or Fe2O3?

4. Which of the following has the greatest mass percentage of oxygen—ThOCl2, MgCO3, or NO2Cl?

5. Calculate the percent composition of the element shown in bold in each compound.

a. SbBr3

b. As2I4

c. AlPO4

d. C6H10O

6. Calculate the percent composition of the element shown in bold in each compound.

a. HBrO3

b CsReO4

c. C3H8O

d. FeSO4

7. A sample of a chromium compound has a molar mass of 151.99 g/mol. Elemental analysis of the compound shows that it contains 68.43% chromium and 31.57% oxygen. What is the identity of the compound?

8. The percentages of iron and oxygen in the three most common binary compounds of iron and oxygen are given in the following table. Write the empirical formulas of these three compounds.

Compound % Iron % Oxygen Empirical Formula
1 69.9 30.1
2 77.7 22.3
3 72.4 27.6

9. What is the mass percentage of water in each hydrate?

a. LiCl·H2O

b. MgSO4·7H2O

c. Sr(NO3)2·4H2O

10. What is the mass percentage of water in each hydrate?

a. CaHPO4·2H2O

b. FeCl2·4H2O

c. Mg(NO3)2·4H2O

11. Two hydrates were weighed, heated to drive off the waters of hydration, and then cooled. The residues were then reweighed. Based on the following results, what are the formulas of the hydrates?

Compound Initial Mass (g) Mass after Cooling (g)
NiSO4·xH2O 2.08 1.22
CoCl2·xH2O 1.62 0.88

12. Which contains the greatest mass percentage of sulfur—FeS2, Na2S2O4, or Na2S?

13. Given equal masses of each, which contains the greatest mass percentage of sulfur—NaHSO4 or K2SO4?

14. Calculate the mass percentage of oxygen in each polyatomic ion.

a. bicarbonate

b. chromate

c. acetate

d. sulfite

15. Calculate the mass percentage of oxygen in each polyatomic ion.

a. oxalate

b. nitrite

c. dihydrogen phosphate

d. thiocyanate

16. The empirical formula of garnet, a gemstone, is Fe3Al2Si3O12. An analysis of a sample of garnet gave a value of 13.8% for the mass percentage of silicon. Is this consistent with the empirical formula?

17. A compound has the empirical formula C2H4O, and its formula mass is 88 g. What is its molecular formula?

18. Mirex is an insecticide that contains 22.01% carbon and 77.99% chlorine. It has a molecular mass of 545.59 g. What is its empirical formula? What is its molecular formula?

19. How many moles of CO2 and H2O will be produced by combustion analysis of 0.010 mol of styrene?

20. How many moles of CO2, H2O, and N2 will be produced by combustion analysis of 0.0080 mol of aniline?

21. How many moles of CO2, H2O, and N2 will be produced by combustion analysis of 0.0074 mol of aspartame?

22. How many moles of CO2, H2O, N2, and SO2 will be produced by combustion analysis of 0.0060 mol of penicillin G?

23. Combustion of a 34.8 mg sample of benzaldehyde, which contains only carbon, hydrogen, and oxygen, produced 101 mg of CO2 and 17.7 mg of H2O.

a. What was the mass of carbon and hydrogen in the sample?

b. Assuming that the original sample contained only carbon, hydrogen, and oxygen, what was the mass of oxygen in the sample?

c. What was the mass percentage of oxygen in the sample?

d. What is the empirical formula of benzaldehyde?

e. The molar mass of benzaldehyde is 106.12 g/mol. What is its molecular formula?

24. Salicylic acid is used to make aspirin. It contains only carbon, oxygen, and hydrogen. Combustion of a 43.5 mg sample of this compound produced 97.1 mg of CO2 and 17.0 mg of H2O.

a. What is the mass of oxygen in the sample?

b. What is the mass percentage of oxygen in the sample?

c. What is the empirical formula of salicylic acid?

d. The molar mass of salicylic acid is 138.12 g/mol. What is its molecular formula?

25. Given equal masses of the following acids, which contains the greatest amount of hydrogen that can dissociate to form H+—nitric acid, hydroiodic acid, hydrocyanic acid, or chloric acid?

26. Calculate the formula mass or the molecular mass of each compound.

a. heptanoic acid (a seven-carbon carboxylic acid)

b. 2-propanol (a three-carbon alcohol)

c. KMnO4

e. sulfurous acid

f. ethylbenzene (an eight-carbon aromatic hydrocarbon)

27. Calculate the formula mass or the molecular mass of each compound.

a. MoCl5

b. B2O3

c. bromobenzene

d. cyclohexene

e. phosphoric acid

f. ethylamine

28. Given equal masses of butane, cyclobutane, and propene, which contains the greatest mass of carbon?

29. Given equal masses of urea [(NH2)2CO] and ammonium sulfate, which contains the most nitrogen for use as a fertilizer?

1. To two decimal places, the percentages are:

a. 5.97%

b. 37.12%

c. 43.22%

3. % oxygen: KMnO4, 40.50%; K2Cr2O7, 38.07%; Fe2O3, 30.06%

5. To two decimal places, the percentages are:

a. 66.32% Br

b. 22.79% As

c. 25.40% P

d. 73.43% C

7. Cr2O3.

9. To two decimal places, the percentages are:

a. 29.82%

b. 51.16%

c. 25.40%

11. NiSO4 · 6H2O and CoCl2 · 6H2O

13. NaHSO4

15.

a. 72.71%

b. 69.55%

c. 65.99%

d. 0%

17. C4H8O2

23.

a. 27.6 mg C and 1.98 mg H

b. 5.2 mg O

c. 15%

d. C7H6O

e. C7H6O

25. hydrocyanic acid, HCN

27. To two decimal places, the values are:

a. 273.23 amu

b. 69.62 amu

c. 157.01 amu

d. 82.14 amu

e. 98.00 amu

f. 45.08 amu

29. Urea

## 3.4: Avogadro's Number and the Mole

### Conceptual Problems

Please be sure you are familiar with the topics discussed in Essential Skills 2 before proceeding to the Conceptual Problems.

1. Describe the relationship between an atomic mass unit and a gram.
2. Is it correct to say that ethanol has a formula mass of 46? Why or why not?
3. If 2 mol of sodium react completely with 1 mol of chlorine to produce sodium chloride, does this mean that 2 g of sodium reacts completely with 1 g of chlorine to give the same product? Explain your answer.
4. Construct a flowchart to show how you would calculate the number of moles of silicon in a 37.0 g sample of orthoclase (KAlSi3O8), a mineral used in the manufacture of porcelain.
5. Construct a flowchart to show how you would calculate the number of moles of nitrogen in a 22.4 g sample of nitroglycerin that contains 18.5% nitrogen by mass.

A = %N by mass, expressed as a decimal

$B = {1 \over \text {molar mass of nitrogen in g} }$

$g \text {nitroglycerin} \underrightarrow {xA} gN \underrightarrow {xB} mol \, N$

### Numerical Problems

Please be sure you are familiar with the topics discussed in Essential Skills 2 before proceeding to the Numerical Problems.

1. Derive an expression that relates the number of molecules in a sample of a substance to its mass and molecular mass.

2. Calculate the molecular mass or formula mass of each compound.

1. KCl (potassium chloride)
2. NaCN (sodium cyanide)
3. H2S (hydrogen sulfide)
4. NaN3 (sodium azide)
5. H2CO3 (carbonic acid)
6. K2O (potassium oxide)
7. Al(NO3)3 (aluminum nitrate)
8. Cu(ClO4)2 [copper(II) perchlorate]

3. Calculate the molecular mass or formula mass of each compound.

1. V2O4 (vanadium(IV) oxide)
2. CaSiO3 (calcium silicate)
3. BiOCl (bismuth oxychloride)
4. CH3COOH (acetic acid)
5. Ag2SO4 (silver sulfate)
6. Na2CO3 (sodium carbonate)
7. (CH3)2CHOH (isopropyl alcohol)

4. Calculate the molar mass of each compound.

a.

b.

c.

d.

e.

5. Calculate the molar mass of each compound.

a.

b.

c.

d.

6. For each compound, write the condensed formula, name the compound, and give its molar mass.

a.

b.

7. For each compound, write the condensed formula, name the compound, and give its molar mass.

a.

b.

8. Calculate the number of moles in 5.00 × 102 g of each substance. How many molecules or formula units are present in each sample?

a. CaO (lime)

b. CaCO3(chalk)

c. C12H22O11 [sucrose (cane sugar)]

d. NaOCl (bleach)

e. CO2 (dry ice)

9. Calculate the mass in grams of each sample.

a. 0.520 mol of N2O4

b. 1.63 mol of C6H4Br2

c. 4.62 mol of (NH4)2SO3

10. Give the number of molecules or formula units in each sample.

a. 1.30 × 10−2 mol of SCl2

b. 1.03 mol of N2O5

c. 0.265 mol of Ag2Cr2O7

11. Give the number of moles in each sample.

a. 9.58 × 1026 molecules of Cl2

b. 3.62 × 1027 formula units of KCl

c. 6.94 × 1028 formula units of Fe(OH)2

12. Solutions of iodine are used as antiseptics and disinfectants. How many iodine atoms correspond to 11.0 g of molecular iodine (I2)?

13. What is the total number of atoms in each sample?

a. 0.431 mol of Li

b. 2.783 mol of methanol (CH3OH)

c. 0.0361 mol of CoCO3

d. 1.002 mol of SeBr2O

14. What is the total number of atoms in each sample?

a. 0.980 mol of Na

b. 2.35 mol of O2

c. 1.83 mol of Ag2S

d. 1.23 mol of propane (C3H8)

15. What is the total number of atoms in each sample?

a. 2.48 g of HBr

b. 4.77 g of CS2

c. 1.89 g of NaOH

d. 1.46 g of SrC2O4

16. Decide whether each statement is true or false and explain your reasoning.

1. There are more molecules in 0.5 mol of Cl2than in 0.5 mol of H2.
2. One mole of H2 has 6.022 × 1023 hydrogen atoms.
3. The molecular mass of H2O is 18.0 amu.
4. The formula mass of benzene is 78 amu.

17. Complete the following table.

Substance Mass (g) Number of Moles Number of Molecules or Formula Units Number of Atoms or Ions
MgCl2 37.62
AgNO3 2.84
BH4Cl 8.93 × 1025
K2S 7.69 × 1026
H2SO4 1.29
C6H14 11.84
HClO3 2.45 × 1026

18. Give the formula mass or the molecular mass of each substance.

1. $$PbClF$$
2. $$Cu_2P_2O_7$$
3. $$BiONO3_$$
4. $$Tl_2SeO_4$$

19. Give the formula mass or the molecular mass of each substance.

1. $$MoCl_5$$
2. $$B_2O_3$$
3. $$UO_2CO_3$$
4. $$NH_4UO_2AsO_4$$

## 3.6: Quantitative Information from Balanced Equations

### Conceptual Problems

1. What information is required to determine the mass of solute in a solution if you know the molar concentration of the solution?

### Numerical Problems

1. Refer to the Breathalyzer test described in Example 8. How much ethanol must be present in 89.5 mL of a person’s breath to consume all the potassium dichromate in a Breathalyzer ampul containing 3.0 mL of a 0.40 mg/mL solution of potassium dichromate?
2. Phosphoric acid and magnesium hydroxide react to produce magnesium phosphate and water. If 45.00 mL of 1.50 M phosphoric acid are used in the reaction, how many grams of magnesium hydroxide are needed for the reaction to go to completion?
3. Barium chloride and sodium sulfate react to produce sodium chloride and barium sulfate. If 50.00 mL of 2.55 M barium chloride are used in the reaction, how many grams of sodium sulfate are needed for the reaction to go to completion?
4. How many grams of sodium phosphate are obtained in solution from the reaction of 75.00 mL of 2.80 M sodium carbonate with a stoichiometric amount of phosphoric acid? A second product is water; what is the third product? How many grams of the third product are obtained?
5. How many grams of ammonium bromide are produced from the reaction of 50.00 mL of 2.08 M iron(II) bromide with a stoichiometric amount of ammonium sulfide? What is the second product? How many grams of the second product are produced?

## 3.7: LIMITING REACTANTS

### Conceptual Problems

1. Engineers use conservation of mass, called a “mass balance,” to determine the amount of product that can be obtained from a chemical reaction. Mass balance assumes that the total mass of reactants is equal to the total mass of products. Is this a chemically valid practice? Explain your answer.
2. Given the equation $2H_{2\;(g)} + O_{2\;(g)} \rightarrow 2H+2O_{(g)},$ is it correct to say that 10 g of hydrogen will react with 10 g of oxygen to produce 20 g of water vapor?
3. What does it mean to say that a reaction is stoichiometric?
4. When sulfur is burned in air to produce sulfur dioxide, what is the limiting reactant? Explain your answer.
5. Is it possible for the percent yield to be greater than the theoretical yield? Justify your answer.

### Numerical Problems

Please be sure you are familiar with the topics discussed in Essential Skills 2 () before proceeding to the Numerical Problems.

12. Write a balanced chemical equation for each reaction and then determine which reactant is in excess.

a. 2.46 g barium(s) plus 3.89 g bromine(l) in water to give barium bromide

b. 1.44 g bromine(l) plus 2.42 g potassium iodide(s) in water to give potassium bromide and iodine

c. 1.852 g of Zn metal plus 3.62 g of sulfuric acid in water to give zinc sulfate and hydrogen gas

d. 0.147 g of iron metal reacts with 0.924 g of silver acetate in water to give iron(II) acetate and silver metal

e. 3.142 g of ammonium phosphate reacts with 1.648 g of barium hydroxide in water to give ammonium hydroxide and barium phosphate

13. Under the proper conditions, ammonia and oxygen will react to form dinitrogen monoxide (nitrous oxide, also called laughing gas) and water. Write a balanced chemical equation for this reaction. Determine which reactant is in excess for each combination of reactants.

a. 24.6 g of ammonia and 21.4 g of oxygen

b. 3.8 mol of ammonia and 84.2 g of oxygen

c. 3.6 × 1024 molecules of ammonia and 318 g of oxygen

d. 2.1 mol of ammonia and 36.4 g of oxygen

14. When a piece of zinc metal is placed in aqueous hydrochloric acid, zinc chloride is produced, and hydrogen gas is evolved. Write a balanced chemical equation for this reaction. Determine which reactant is in excess for each combination of reactants.

a. 12.5 g of HCl and 7.3 g of Zn

b. 6.2 mol of HCl and 100 g of Zn

c. 2.1 × 1023 molecules of Zn and 26.0 g of HCl

d. 3.1 mol of Zn and 97.4 g of HCl

15. Determine the mass of each reactant needed to give the indicated amount of product. Be sure that the chemical equations are balanced.

a. NaI(aq) + Cl2(g) → NaCl(aq) + I2(s); 1.0 mol of NaCl

b. NaCl(aq) + H2SO4(aq) → HCl(g) + Na2SO4(aq); 0.50 mol of HCl

c. NO2(g) + H2O(l) → HNO2(aq) + HNO3(aq); 1.5 mol of HNO3

16. Determine the mass of each reactant needed to give the indicated amount of product. Be sure that the chemical equations are balanced.

a. AgNO3(aq) + CaCl2(s) → AgCl(s) + Ca(NO3)2(aq); 1.25 mol of AgCl

b. Pb(s) + PbO2(s) + H2SO4(aq) → PbSO4(s) + H2O(l); 3.8 g of PbSO4

c. H3PO4(aq) + MgCO3(s) → Mg3(PO4)2(s) + CO2(g) + H2O(l); 6.41 g of Mg3(PO4)2

17. Determine the percent yield of each reaction. Be sure that the chemical equations are balanced. Assume that any reactants for which amounts are not given are in excess. (The symbol Δ indicates that the reactants are heated.)

a. KClO3(s) $$\underrightarrow {\Delta}$$ KCl(s)+O2(g);2.14 g of KClO3 produces 0.67 g of O2

b. Cu(s) + H2SO4(aq) → CuSO4(aq) + SO2(g) + H2O(l); 4.00 g of copper gives 1.2 g of sulfur dioxide

c. AgC2H3O2(aq) + Na3PO4(aq) → Ag3PO4(s) + NaC2H3O2(aq); 5.298 g of silver acetate produces 1.583 g of silver phosphate

18. Each step of a four-step reaction has a yield of 95%. What is the percent yield for the overall reaction?

19. A three-step reaction yields of 87% for the first step, 94% for the second, and 55% for the third. What is the percent yield of the overall reaction?

20. Give a general expression relating the theoretical yield (in grams) of product that can be obtained from x grams of B, assuming neither A nor B is limiting.

A + 3B → 2C

21. Under certain conditions, the reaction of hydrogen with carbon monoxide can produce methanol.

a. Write a balanced chemical equation for this reaction.

b. Calculate the percent yield if exactly 200 g of methanol is produced from exactly 300 g of carbon monoxide.

22. Chlorine dioxide is a bleaching agent used in the paper industry. It can be prepared by the following reaction:

NaClO2(s) + Cl2(g) → ClO2(aq) + NaCl(aq)

a. What mass of chlorine is needed for the complete reaction of 30.5 g of NaClO2?

b. Give a general equation for the conversion of x grams of sodium chlorite to chlorine dioxide.

23. The reaction of propane gas (CH3CH2CH3) with chlorine gas (Cl2) produces two monochloride products: CH3CH2CH2Cl and CH3CHClCH3. The first is obtained in a 43% yield and the second in a 57% yield.

a. If you use 2.78 g of propane gas, how much chlorine gas would you need for the reaction to go to completion?

b. How many grams of each product could theoretically be obtained from the reaction starting with 2.78 g of propane?

c. Use the actual percent yield to calculate how many grams of each product would actually be obtained.

24. Protactinium (Pa), a highly toxic metal, is one of the rarest and most expensive elements. The following reaction is one method for preparing protactinium metal under relatively extreme conditions:

$2PaI_5 (s) \underrightarrow {\Delta} 2Pa (s) + 5I_2 (s)$

a. Given 15.8 mg of reactant, how many milligrams of protactinium could be synthesized?

b. If 3.4 mg of Pa was obtained, what was the percent yield of this reaction?

c. If you obtained 3.4 mg of Pa and the percent yield was 78.6%, how many grams of PaI5 were used in the preparation?

25. Aniline (C6H5NH2) can be produced from chlorobenzene (C6H5Cl) via the following reaction:

C6H5Cl(l) + 2NH3(g) → C6H5NH2(l) + NH4Cl(s)

Assume that 20.0 g of chlorobenzene at 92% purity is mixed with 8.30 g of ammonia.

a. Which is the limiting reactant?

b. Which reactant is present in excess?

c. What is the theoretical yield of ammonium chloride in grams?

d. If 4.78 g of NH4Cl was recovered, what was the percent yield?

e. Derive a general expression for the theoretical yield of ammonium chloride in terms of grams of chlorobenzene reactant, if ammonia is present in excess.

26. A stoichiometric quantity of chlorine gas is added to an aqueous solution of NaBr to produce an aqueous solution of sodium chloride and liquid bromine. Write the chemical equation for this reaction. Then assume an 89% yield and calculate the mass of chlorine given the following:

a. 9.36 × 1024 formula units of NaCl

b. 8.5 × 104 mol of Br2

c. 3.7 × 108 g of NaCl

13. The balanced chemical equation for this reaction is

2NH3 + 2O2 → N2O + 3H2O

a. NH3

b. NH3

c. O2

d. NH3

15.

a. 150 g NaI and 35 g Cl2

b. 29 g NaCl and 25 g H2SO4

c. 140 g NO2 and 27 g H2O

17.

a. 80%

b. 30%

c. 35.7%

19. 45%.

21.

a. CO + 2H2 → CH3OH

b. 58.28%

23.

a. 2.24 g Cl2

b. 4.95 g

c. 2.13 g CH3CH2CH2Cl plus 2.82 g CH3CHClCH3

25.

a. chlorobenzene

b. ammonia

c. 8.74 g ammonium chloride.

d. 55%

e. $$Theoretical \, yield \, (NH_4Cl) = {mass \, of \, chlorobenzene \, (g) \times 0.92 \times \times 53.49 \, g/mol \over 112.55 \, g/mol}$$

### Conceptual Problems II

1. Engineers use conservation of mass, called a “mass balance,” to determine the amount of product that can be obtained from a chemical reaction. Mass balance assumes that the total mass of reactants is equal to the total mass of products. Is this a chemically valid practice? Explain your answer.
2. Given the equation $2H_{2\;(g)} + O_{2\;(g)} \rightarrow 2H+2O_{(g)},$ is it correct to say that 10 g of hydrogen will react with 10 g of oxygen to produce 20 g of water vapor?
3. What does it mean to say that a reaction is stoichiometric?
4. When sulfur is burned in air to produce sulfur dioxide, what is the limiting reactant? Explain your answer.
5. Is it possible for the percent yield to be greater than the theoretical yield? Justify your answer.

### Numerical Problems II

Please be sure you are familiar with the topics discussed in Essential Skills 2 () before proceeding to the Numerical Problems.

17. Determine the percent yield of each reaction. Be sure that the chemical equations are balanced. Assume that any reactants for which amounts are not given are in excess. (The symbol Δ indicates that the reactants are heated.)

a. KClO3(s) $$\underrightarrow {\Delta}$$ KCl(s)+O2(g);2.14 g of KClO3 produces 0.67 g of O2

b. Cu(s) + H2SO4(aq) → CuSO4(aq) + SO2(g) + H2O(l); 4.00 g of copper gives 1.2 g of sulfur dioxide

c. AgC2H3O2(aq) + Na3PO4(aq) → Ag3PO4(s) + NaC2H3O2(aq); 5.298 g of silver acetate produces 1.583 g of silver phosphate

18. Each step of a four-step reaction has a yield of 95%. What is the percent yield for the overall reaction?

19. A three-step reaction yields of 87% for the first step, 94% for the second, and 55% for the third. What is the percent yield of the overall reaction?

20. Give a general expression relating the theoretical yield (in grams) of product that can be obtained from x grams of B, assuming neither A nor B is limiting.

A + 3B → 2C

21. Under certain conditions, the reaction of hydrogen with carbon monoxide can produce methanol.

a. Write a balanced chemical equation for this reaction.

b. Calculate the percent yield if exactly 200 g of methanol is produced from exactly 300 g of carbon monoxide.

22. Chlorine dioxide is a bleaching agent used in the paper industry. It can be prepared by the following reaction:

NaClO2(s) + Cl2(g) → ClO2(aq) + NaCl(aq)

a. What mass of chlorine is needed for the complete reaction of 30.5 g of NaClO2?

b. Give a general equation for the conversion of x grams of sodium chlorite to chlorine dioxide.

23. The reaction of propane gas (CH3CH2CH3) with chlorine gas (Cl2) produces two monochloride products: CH3CH2CH2Cl and CH3CHClCH3. The first is obtained in a 43% yield and the second in a 57% yield.

a. If you use 2.78 g of propane gas, how much chlorine gas would you need for the reaction to go to completion?

b. How many grams of each product could theoretically be obtained from the reaction starting with 2.78 g of propane?

c. Use the actual percent yield to calculate how many grams of each product would actually be obtained.

24. Protactinium (Pa), a highly toxic metal, is one of the rarest and most expensive elements. The following reaction is one method for preparing protactinium metal under relatively extreme conditions:

$2PaI_5 (s) \underrightarrow {\Delta} 2Pa (s) + 5I_2 (s)$

a. Given 15.8 mg of reactant, how many milligrams of protactinium could be synthesized?

b. If 3.4 mg of Pa was obtained, what was the percent yield of this reaction?

c. If you obtained 3.4 mg of Pa and the percent yield was 78.6%, how many grams of PaI5 were used in the preparation?

25. Aniline (C6H5NH2) can be produced from chlorobenzene (C6H5Cl) via the following reaction:

C6H5Cl(l) + 2NH3(g) → C6H5NH2(l) + NH4Cl(s)

Assume that 20.0 g of chlorobenzene at 92% purity is mixed with 8.30 g of ammonia.

a. Which is the limiting reactant?

b. Which reactant is present in excess?

c. What is the theoretical yield of ammonium chloride in grams?

d. If 4.78 g of NH4Cl was recovered, what was the percent yield?

e. Derive a general expression for the theoretical yield of ammonium chloride in terms of grams of chlorobenzene reactant, if ammonia is present in excess.

26. A stoichiometric quantity of chlorine gas is added to an aqueous solution of NaBr to produce an aqueous solution of sodium chloride and liquid bromine. Write the chemical equation for this reaction. Then assume an 89% yield and calculate the mass of chlorine given the following:

a. 9.36 × 1024 formula units of NaCl

b. 8.5 × 104 mol of Br2

c. 3.7 × 108 g of NaCl

### Numerical Answers II

17.

a. 80%

b. 30%

c. 35.7%

19. 45%.

21.

a. CO + 2H2 → CH3OH

b. 58.28%

23.

a. 2.24 g Cl2

b. 4.95 g

c. 2.13 g CH3CH2CH2Cl plus 2.82 g CH3CHClCH3

25.

a. chlorobenzene

b. ammonia

c. 8.74 g ammonium chloride.

d. 55%

e. $$Theoretical \, yield \, (NH_4Cl) = {mass \, of \, chlorobenzene \, (g) \times 0.92 \times \times 53.49 \, g/mol \over 112.55 \, g/mol}$$

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