Chapter 11

Challenge For each of the following, balance the chemical equation; interpret the equation in terms of particles, moles, and mass; and show that the law of conservation of mass is observed. a) ____\(\mathrm{Na}(\mathrm{s})+\)____\(\mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow\) ____\(\mathrm{NaOH}(\mathrm{aq})+\) ____\(\mathrm{H}_{2}(\mathrm{g})\) b) ____\(Z n(s)+\) ____\(\mathrm{HNO}_{3}(\mathrm{aq}) \rightarrow\) ____\(\mathrm{Zn}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+\) ____\(\mathrm{H}_{2} \mathrm{O}(\mathrm{l})\)

Determine all possible mole ratios for the following balanced chemical equations. a) \(4 \mathrm{Al}(\mathrm{s})+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{s})\) b) \(3 \mathrm{Fe}(\mathrm{s})+4 \mathrm{H}_{2} \mathrm{O}\left(\mathrm{l} \rightarrow \mathrm{Fe}_{3} \mathrm{O}_{4}(\mathrm{s})+4 \mathrm{H}_{2}(\mathrm{g})\right.\) c) \(2 \mathrm{HgO}(\mathrm{s}) \rightarrow 2 \mathrm{Hg}(\mathrm{l})+\mathrm{O}_{2}(\mathrm{g})\)

Challenge Balance the following equations, and determine the possible mole ratios. a. \(\mathrm{ZnO}(\mathrm{s})+\mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{ZnCl}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})\) b. butane \(\left(\mathrm{C}_{4} \mathrm{H}_{10}\right)+\) oxygen \(\rightarrow\) carbon dioxide \(+\) water

Compare the mass of the reactants and the mass of the products in a chemical reaction, and explain how these masses are related.

State how many mole ratios can be written for a chemical reaction involving three substances.

Categorize the ways in which a balanced chemical equation can be interpreted.

Apply The general form of a chemical reaction is \(x A+y B \rightarrow z A B\) . In the equation, A and \(B\) are elements, and \(x, y,\) and \(z\) are coefficients. State the mole ratios for this reaction.

Apply Hydrogen peroxide (H \(_{2} \mathrm{O}_{2} )\) decomposes to produce water and oxygen. Write a balanced chemical equation for this reaction, and determine the possible mole ratios.

Model Write the mole ratios for the reaction of hydrogen gas and oxygen gas, \(2 \mathrm{H}_{2}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{H}_{2} 0\) . Make a sketch of six hydrogen molecules reacting with the correct number of oxygen molecules. Show the water molecules produced.

Methane and sulfur react to produce carbon disulfide (C S 2), a liquid often used in the production of cellophane. ___\(\mathrm{CH}_{4}(\mathrm{g})+\) ___ \(\mathrm{S}_{8}(\mathrm{s}) \rightarrow\) ___\(\mathrm{CS}_{2}(\mathrm{l})+\) ___\(\mathrm{H}_{2} \mathrm{S}(\mathrm{g})\) a. Balance the equation. b. Calculate the moles of \(\mathrm{CS}_{2}\) produced when 1.50 \(\mathrm{mol} \mathrm{S}_{8}\) is used. c. How many moles of \(\mathrm{H}_{2} \mathrm{S}\) is produced?

Challenge Sulfuric acid \(\left(\mathrm{H}_{2} \mathrm{SO}_{4}\right)\) is formed when sulfur dioxide (SO_{2} ) reacts with oxygen and water. a. Write the balanced chemical equation for the reaction. b. How many moles of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) is produced from 12.5 \(\mathrm{moles}\) of \(\mathrm{SO}_{2} ?\) c. How many moles of \(\mathrm{O}_{2}\) are needed?

Challenge Titanium is a transition metal used in many alloys because it is extremely strong and lightweight. Titanium tetrachloride \(\left(\mathrm{TiCl}_{4}\right)\) is extracted from titanium oxide \(\left(\mathrm{TiO}_{2}\right)\) using chlorine and coke (carbon). $$\mathrm{TiO}_{2}(\mathrm{s})+\mathrm{C}(\mathrm{s})+2 \mathrm{Cl}_{2}(\mathrm{g}) \rightarrow \mathrm{TiCl}_{4}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{g})$$ a. What mass of \(\mathrm{Cl}_{2}\) gas is needed to react with 1.25 \(\mathrm{mol}\) of \(\mathrm{TiO}_{2} ?\) b. What mass of \(C\) is needed to react with 1.25 mol of TiO \(_{2} ?\) c. What is the mass of all of the products formed by reaction with 1.25 \(\mathrm{mol}\) of \(\mathrm{TiO}_{2} ?\)

One of the reactions used to inflate automobile air bags involves sodium azide \(\left(\mathrm{NaN}_{3}\right) : 2 \mathrm{NaN}_{3}(\mathrm{s}) \rightarrow 2 \mathrm{Na}(\mathrm{s})+3 \mathrm{N}_{2}(\mathrm{g})\) mass of \(\mathrm{N}_{2}\) produced from the decomposition of NaN \(_{3}\) shown at right.

Challenge In the formation of acid rain, sulfur dioxide \(\left(\mathrm{SO}_{2}\right)\) reacts with oxygen and water in the air to form sulfuric acid \(\left(\mathrm{H}_{2} \mathrm{SO}_{4}\right)\) Write the balanced chemical equation for the reaction. If 2.50 g of \(\mathrm{SO}_{2}\) reacts with excess oxygen and water, how much \(\mathrm{H}_{2} \mathrm{SO}_{4}\) in grams, is produced?

Explain why a balanced chemical equation is needed to solve a stoichiometric problem.

List the four steps used in solving stoichiometric problems.

Describe how a mole ratio is correctly expressed when it is used to solve a stoichiometric problem.

Calculate Hydrogen reacts with excess nitrogen as follows: $$\mathrm{N}_{2}(\mathrm{g})+3 \mathrm{H}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{NH}_{3}(\mathrm{g})$$ If 2.70 g of \(\mathrm{H}_{2}\) reacts, how many grams of \(\mathrm{NH}_{3}\) is formed?

Design a concept map for the following reaction. $$\mathrm{CaCO}_{3}(\mathrm{s})+2 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{CaCl}_{2}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(1)+\mathrm{CO}_{2}(\mathrm{g})$$ The concept map should explain how to determine the mass of \(\mathrm{CaCl}_{2}\) produced from a given mass of HCl.

The reaction between solid sodium and iron(III) oxide is one in a series of reactions that inflates an automobile airbag: \(6 \mathrm{Na}(\mathrm{s})+\mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{s}) \rightarrow 3 \mathrm{Na}_{2} \mathrm{O}(\mathrm{s})+2 \mathrm{Fe}(\mathrm{s}) .\) If 100.0 \(\mathrm{g}\) of \(\mathrm{Na}\) and 100.0 \(\mathrm{g}\) of \(\mathrm{Fe}_{2} \mathrm{O}_{3}\) are used in this reaction, determine the following. a. limiting reactant b. reactant in excess c. mass of solid iron produced d. mass of excess reactant that remains after the reaction is complete

Challenge Photosynthesis reactions in green plants use carbon dioxide and water to produce glucose \(\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right)\) and oxygen. A plant has 88.0 g of carbon dioxide and 64.0 g of water available for photosynthesis. a. Write the balanced chemical equation for the reaction. b. Determine the limiting reactant. c. Determine the excess reactant. d. Determine the mass in excess. e. Determine the mass of glucose produced.

Describe the reason why a reaction between two substances comes to an end.

Analyze Tetraphosphorus trisulphide \(\left(\mathrm{P}_{4} \mathrm{S}_{3}\right)\) is used in the match heads of some matches. It is produced in the reaction \(8 \mathrm{P}_{4}+3 \mathrm{S}_{8} \rightarrow 8 \mathrm{P}_{4} \mathrm{S}_{3}\) Determine which of the following statements are incorrect, and rewrite the incorrect statements to make them correct. a. 4 mol \(P_{4}\) reacts with 1.5 mol \(S_{8}\) to form 4 mol \(P_{4} S_{3}\) b. Sulfur is the limiting reactant when 4 \(\mathrm{mol} \mathrm{P}_{4}\) and 4 \(\mathrm{mol} \mathrm{S}_{8}\) react. c. 6 mol \(P_{4}\) reacts with 6 mol \(S_{8},\) forming 1320 \(\mathrm{g} \mathrm{P}_{4} \mathrm{S}_{3}\)

Aluminum hydroxide \(\left(\mathrm{Al}(\mathrm{OH})_{3}\right)\) is often present in antacids to neutralize stomach acid \((\mathrm{HCl})\) The reaction occurs as follows: \(\mathrm{Al}(\mathrm{OH})_{3}(\mathrm{s})+3 \mathrm{HCl}(\mathrm{aq}) \rightarrow \mathrm{AlCl}_{3}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{D}) .\) If 14.0 \(\mathrm{g}\) of \(\mathrm{Al}(\mathrm{OH})_{3}\) is present in an antacid tablet, determine the theoretical yield of \(\mathrm{AlCl}_{3}\) produced when the tablet reacts with \(\mathrm{HCl}\)

Challenge When copper wire is placed into a silver nitrate solution \(\left(\mathrm{AgNO}_{3}\right)\), silver crystals and copper(II) nitrate \(\left(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}\right)\) solution form. a. Write the balanced chemical equation for the reaction. b. If a 20.0-g sample of copper is used, determine the theoretical yield of silver. c. If 60.0 g of silver is recovered from the reaction, determine the percent yield of the reaction.

Identify which type of yield- theoretical yield, actual yield, or percent yield - is a measure of the efficiency of a chemical reaction.

List several reasons why the actual yield from a chemical reaction is not usually equal to the theoretical yield.

Explain how percent yield is calculated.

Apply In an experiment, you combine 83.77 g of iron with an excess of sulfur and then heat the mixture to obtain iron(lill) sulfide. $$2 \mathrm{Fe}(\mathrm{s})+3 \mathrm{S}(\mathrm{s}) \rightarrow \mathrm{Fe}_{2} \mathrm{S}_{3}(\mathrm{s})$$ What is the theoretical yield, in grams, of iron(III) sulfide?

Why must a chemical equation be balanced before you can determine mole ratios?

What relationships can be determined from a balanced chemical equation?

Explain why mole ratios are central to stoichiometric calculations.

Why are coefficients used in mole ratios instead of subscripts?

Explain how the conservation of mass allows you to interpret a balanced chemical equation in terms of mass.

When heated by a flame, ammonium dichromate decomposes, producing nitrogen gas, solid chromium(III) oxide, and water vapor. $$\left(\mathrm{NH}_{4}\right) 2 \mathrm{Cr}_{2} \mathrm{O}_{7} \rightarrow \mathrm{N}_{2}+\mathrm{Cr}_{2} \mathrm{O}_{3}+4 \mathrm{H}_{2} \mathrm{O}$$ Write the mole ratios for this reaction that relate ammonium dichromate to the products.

Interpret the following equation in terms of particles, moles, and mass. $$4 \mathrm{Al}(\mathrm{s})+3 \mathrm{O}_{2}(\mathrm{g}) \rightarrow 2 \mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{s})$$

Smelting When tin(IV) oxide is heated with carbon in a process called smelting, the element tin can be extracted. $$\mathrm{SnO}_{2}(\mathrm{s})+2 \mathrm{C}(\mathrm{s}) \rightarrow \mathrm{Sn}(1)+2 \mathrm{CO}(\mathrm{g})$$ Interpret the chemical equation in terms of particles, moles, and mass.

When solid copper is added to nitric acid, copper(II) nitrate, nitrogen dioxide, and water are produced. Write the balanced chemical equation for the reaction. List six mole ratios for the reaction.

When hydrochloric acid solution reacts with lead(II) nitrate solution, lead(II) chloride precipitates and a solution of nitric acid is produced. a. Write the balanced chemical equation for the reaction. b. Interpret the equation in terms of molecules and formula units, moles, and mass.

When aluminum is mixed with iron(III) oxide, iron metal and aluminum oxide are produced, along with a large quantity of heat. What mole ratio would you use to determine moles of Fe if moles of Fe_ \(\mathrm{O}_{3}\) is known? \(\mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{s})+2 \mathrm{Al}(\mathrm{s}) \rightarrow 2 \mathrm{Fe}(\mathrm{s})+\mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{s})+\) heat

Solid silicon dioxide, often called silica, reacts with hydrofluoric acid (HF) solution to produce the gas silicon tetrafluoride and water. a. Write the balanced chemical equation for the reaction. b. List three mole ratios, and explain how you would use them in stoichiometric calculations.

The most important commercial ore of chromium is chromite \(\left(\mathrm{FeCr}_{2} \mathrm{O}_{4}\right)\) One of the steps in the process used to extract chromium from the ore is the reaction of chromite with coke (carbon) to produce ferrochrome \(\left(\mathrm{FeCr}_{2}\right)\) $$2 \mathrm{C}(\mathrm{s})+\mathrm{Fe} \mathrm{Cr}_{2} \mathrm{O}_{4}(\mathrm{s}) \rightarrow \mathrm{FeCr}_{2}(\mathrm{s})+2 \mathrm{CO}_{2}(\mathrm{g})$$ What mole ratio would you use to convert from moles of chromite to moles of ferrochrome?

Air Pollution The pollutant \(\mathrm{SO}_{2}\) is removed from the air by in a reaction that also involves calcium carbonate and oxygen. The products of this reaction are calcium sulfate and carbon dioxide. Determine the mole ratio you would use to convert moles of \(\mathrm{SO}_{2}\) to moles of \(\mathrm{CaSO}_{4}\)

Two substances, W and X, react to form the products Y and Z. Table 11.2 shows the moles of the reactants and products involved when the reaction was carried out. Use the data to determine the coefficients that will balance the equation \(\mathrm{W}+\mathrm{X} \rightarrow \mathrm{Y}+\mathrm{Z}\)

Antacids Magnesium hydroxide is an ingredient in some antacids. Antacids react with excess hydrochloric acid in the stomach to relieve indigestion. ___ \(\mathrm{Mg}(\mathrm{OH})_{2}+\) ___ \(\mathrm{HCl} \rightarrow\) ___ \(\mathrm{MgCl}_{2}+\) ___ \(\mathrm{H}_{2} \mathrm{O}\) a. Balance the reaction of \(\mathrm{Mg}(\mathrm{OH})_{2}\) with \(\mathrm{HCl}\) . b. Write the mole ratio that would be used to determine the number of moles of MgCl_ produced when HCl reacts with \(\mathrm{Mg}(\mathrm{OH})_{2}\)

What is the first step in all stoichiometric calculations?

What information does a balanced equation provide?

On what law is stoichometry based, and how do the calculations support this law?

How is molar mass used in some stoichiometric calculations?

What information must you have in order to calculate the mass of product formed in a chemical reaction?