3.E: Exercises

Last updated
Save as PDF

Page ID: 39084

\( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

3.1: Chemical Equations

Conceptual Problems

How does a balanced chemical equation agree with the law of definite proportions?
What is the difference between S₈ and 8S? Use this example to explain why subscripts in a formula must not be changed.
What factors determine whether a chemical equation is balanced?
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.

3.2: Some Simple Patterns of Chemical Reactivity

3.3: Formula Masses

Conceptual Problems

What is the relationship between an empirical formula and a molecular formula
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
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

d. tetraethyllead

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?

Numerical Answers

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.

Describe the relationship between an atomic mass unit and a gram.
Is it correct to say that ethanol has a formula mass of 46? Why or why not?
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.
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.
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.

Conceptual Answer

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.

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

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

V₂O₄ (vanadium(IV) oxide)
CaSiO₃ (calcium silicate)
BiOCl (bismuth oxychloride)
CH₃COOH (acetic acid)
Ag₂SO₄ (silver sulfate)
Na₂CO₃ (sodium carbonate)
(CH₃)₂CHOH (isopropyl alcohol)

4. Calculate the molar mass of each compound.

5. Calculate the molar mass of each compound.

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

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

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.

There are more molecules in 0.5 mol of Cl₂than in 0.5 mol of H₂.
One mole of H₂ has 6.022 × 10²³ hydrogen atoms.
The molecular mass of H₂O is 18.0 amu.
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.

\(PbClF\)
\(Cu_2P_2O_7\)
\(BiONO3_\)
\(Tl_2SeO_4\)

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

\(MoCl_5\)
\(B_2O_3\)
\(UO_2CO_3\)
\(NH_4UO_2AsO_4\)

3.6: Empirical Formulas from Analysis

3.6: Quantitative Information from Balanced Equations

Conceptual Problems

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

Numerical Problems

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?
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?
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?
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?
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

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.
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?
What does it mean to say that a reaction is stoichiometric?
When sulfur is burned in air to produce sulfur dioxide, what is the limiting reactant? Explain your answer.
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

Numerical Answers

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

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.
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?
What does it mean to say that a reaction is stoichiometric?
When sulfur is burned in air to produce sulfur dioxide, what is the limiting reactant? Explain your answer.
Is it possible for the percent yield to be greater than the theoretical yield? Justify your answer.

Numerical Problems II