Chapter 3

What information does a balanced chemical equation provide?

For each of the following, does the oxidation number increase or decrease in the course of a redox reaction? (a) An oxidizing agent (b) A reducing agent (c) A substance undergoing oxidation (d) A substance undergoing reduction

What is meant by the statement, "The reactants were present in stoichiometric amounts"?

Write all the possible mole ratios for the reaction $$3 \mathrm{MgO}(\mathrm{s})+2 \mathrm{Fe}(\mathrm{s}) \longrightarrow \mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{~s})+3 \mathrm{Mg}(\mathrm{s})$$

When asked, "What is the limiting reactant?" you might be tempted to choose the reactant with the smallest mass. Why is this not a good strategy?

Does the limiting reactant determine the theoretical yield, actual yield, or both? Explain.

For this reaction, fill in the table with the indicated quantities for the balanced equation. $$4 \mathrm{NH}_{3}(\mathrm{~g})+5 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 4 \mathrm{NO}(\mathrm{g})+6\mathrm{H}_{2} \mathrm{O}(\mathrm{g})$$ $$\begin{array}{|l|l|l|l|l|}\hline & \mathrm{NH}_{3} & \mathrm{O}_{2} & \mathrm{NO} & \mathrm{H}_{2} \mathrm{O} \\\\\hline \text { No. of molecules } & & & & \\ \hline \text { No. of atoms } & & & & \\\\\hline \begin{array}{l}\text { Amount of } \\\\\text { molecules }\end{array} & & & & \\\\\hline \text { Mass } & & & & \\\\\hline \begin{array}{l}\text { Total mass } \\\\\text { of reactants }\end{array} & & & \\\\\hline \begin{array}{l}\text { Total mass } \\\\\text { of products }\end{array} & & & & \\\\\hline\end{array}$$

Given this equation, $$4 \mathrm{~A}_{2}+3 \mathrm{~B} \longrightarrow \mathrm{B}_{3} \mathrm{~A}_{8}$$ use a diagram to illustrate the number of molecules of reactant A and product \(\mathrm{B}_{3} \mathrm{~A}_{8}\) that would be needed/produced from the reaction of six atoms of \(\mathrm{B}\).

Balance this equation and determine which box represents reactants and which box represents products. $$\mathrm{Sb}(\mathrm{g})+\mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow \mathrm{SbCl}_{3}(\mathrm{~g})$$

Balance these equations. (a) \(\mathrm{UO}_{2}(\mathrm{~s})+\mathrm{HF}(\ell) \longrightarrow \mathrm{UF}_{4}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(\ell)\) (b) \(\mathrm{B}_{2} \mathrm{O}_{3}(\mathrm{~s})+\mathrm{HF}(\ell) \longrightarrow \mathrm{BF}_{3}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\ell)\) (c) \(\mathrm{BF}_{3}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow \mathrm{HF}(\ell)+\mathrm{H}_{3} \mathrm{BO}_{3}(\mathrm{~s})\)

Balance these equations. (a) \(\mathrm{MgO}(\mathrm{s})+\mathrm{Fe}(\mathrm{s}) \longrightarrow \mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{~s})+\mathrm{Mg}(\mathrm{s})\) (b) \(\mathrm{H}_{3} \mathrm{BO}_{3}(\mathrm{~s}) \longrightarrow \mathrm{B}_{2} \mathrm{O}_{3}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(\ell)\) (c) \(\mathrm{NaNO}_{3}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})+\mathrm{HNO}_{3}(\mathrm{~g})\)

Balance these equations. (a) Reaction to produce hydrazine, \(\mathrm{N}_{2} \mathrm{H}_{4}:$$$ \mathrm{H}_{2} \mathrm{NCl}(\mathrm{aq})+\mathrm{NH}_{3}(\mathrm{~g}) \longrightarrow \mathrm{NH}_{4}\mathrm{Cl}(\mathrm{aq})+\mathrm{N}_{2} \mathrm{H}_{4}(\mathrm{aq})$$ (b) Reaction of the fuels (dimethylhydrazine and dinitrogen tetraoxide) used in the Space Shuttle: \)\left(\mathrm{CH}_{3}\right)_{2} \mathrm{~N}_{2} \mathrm{H}_{2}(\ell)+\mathrm{N}_{2} \mathrm{O}_{4}(\mathrm{~g}) \longrightarrow\( $$\mathrm{N}_{2}(\mathrm{~g})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g})+\mathrm{CO}_{2}(\mathrm{~g})$$ (c) Reaction of calcium carbide with water to produce acetylene, \)\mathrm{C}_{2} \mathrm{H}_{2}$ $$\mathrm{CaC}_{2}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2(\mathrm{~s})+\mathrm{C}_{2} \mathrm{H}_{2}(\mathrm{~g})$$

Balance these equations. (a) Reaction of calcium cyanamide to produce ammonia: $$\mathrm{CaNCN}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow \mathrm{CaCO}_{3}(\mathrm{~s})+\mathrm{NH}_{3}(\mathrm{~g}) $$ (b) Reaction to produce diborane, \(\mathrm{B}_{2} \mathrm{H}_{6}:\) $$ \mathrm{NaBH}_{4}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow \mathrm{B}_{2} \mathrm{H}_{6}(\mathrm{~g})+\mathrm{H}_{2}(\mathrm{~g})+\mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq}) $$ (c) Reaction to rid water of hydrogen sulfide, \(\mathrm{H}_{2} \mathrm{~S},\) a foulsmelling compound: $$ \mathrm{H}_{2} \mathrm{~S}(\mathrm{aq})+\mathrm{Cl}_{2}(\mathrm{aq}) \longrightarrow \mathrm{S}_{8}(\mathrm{~s})+\mathrm{HCl}(\mathrm{aq}) $$

Balance these combustion reactions. (a) \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}+\mathrm{O}_{2} \longrightarrow \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\) (b) \(\mathrm{C}_{5} \mathrm{H}_{12}+\mathrm{O}_{2} \longrightarrow \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{C}_{7} \mathrm{H}_{14} \mathrm{O}_{2}+\mathrm{O}_{2} \longrightarrow \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\) (d) \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{O}_{2}+\mathrm{O}_{2} \longrightarrow \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\)

For each substance, what ions are present in an aqueous solution? (a) \(\mathrm{KOH}\) (b) \(\mathrm{K}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{NaNO}_{3}\) (d) \(\mathrm{NH}_{4} \mathrm{Cl}\)

For each substance, what ions are present in an aqueous solution? (a) \(\mathrm{CaI}_{2}\) (b) \(\mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right)_{2}\) (c) NiS (d) \(\mathrm{MgBr}_{2}\)

Which substance conducts electricity when dissolved in water? (a) \(\mathrm{NaCl}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (propane) (c) \(\mathrm{CH}_{3} \mathrm{OH}\) (methanol) (d) \(\mathrm{Ca}\left(\mathrm{NO}_{3}\right)_{2}\)

Which substance conducts electricity when dissolved in water? (a) \(\mathrm{NH}_{4} \mathrm{Cl}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (butane) (c) \(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\) (table sugar) (d) \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\)

Predict whether each compound is soluble in water. Indicate which ions are present in solution for the watersoluble compounds. (a) Potassium monohydrogen phosphate (b) Sodium hypochlorite (c) Magnesium chloride (d) Calcium hydroxide (e) Aluminum bromide

Predict whether each compound is soluble in water. Indicate which ions are present in solution for the watersoluble compounds. (a) Ammonium nitrate (b) Barium sulfate (c) Potassium acetate (d) Calcium carbonate (e) Sodium perchlorate

If aqueous solutions of potassium carbonate and copper(II) nitrate are mixed, a precipitate is formed. Write the complete and net ionic equations for this reaction, and name the precipitate.

If aqueous solutions of potassium sulfide and iron(III) chloride are mixed, a precipitate is formed. Write the complete and net ionic equations for this reaction, and name the precipitate.

Aluminum is obtained from bauxite, which is not a specific mineral but a name applied to a mixture of minerals. One of those minerals, which can dissolve in acids, is gibbsite, \(\mathrm{Al}(\mathrm{OH})_{3} .\) Write balanced overall and net ionic equations for the reaction of gibbsite with sulfuric acid.

Write an overall balanced equation for the precipitation reaction that occurs when aqueous lead(II) nitrate is mixed with an aqueous solution of potassium chloride. Name each reactant and product. Indicate the state of each substance \((\mathrm{s}, \ell, \mathrm{g},\) or aq \()\).

Write an overall balanced equation for the precipitation reaction that occurs when aqueous copper(II) nitrate is mixed with an aqueous solution of sodium carbonate. Name each reactant and product. Indicate the state of each substance \((\mathrm{s}, \ell, \mathrm{g},\) or aq \()\).

Classify each of these as an acid or a base. Which are strong and which are weak? What ions are produced when each is dissolved in water? (a) \(\mathrm{KOH}\) (b) \(\mathrm{Mg}(\mathrm{OH})_{2}\) (c) \(\mathrm{HClO}\) (d) \(\mathrm{HBr}\) (e) \(\mathrm{LiOH}\) (f) \(\mathrm{H}_{2} \mathrm{SO}_{3}\)

Classify each of these as an acid or a base. Which are strong and which are weak? What ions are produced when each is dissolved in water? (a) \(\mathrm{HNO}_{3}\) (b) \(\mathrm{Ca}(\mathrm{OH})_{2}\) (c) \(\mathrm{NH}_{3}\) (d) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) (e) \(\mathrm{KOH}\) (f) \(\mathrm{CH}_{3} \mathrm{COOH}\)

Identify the acid and base used to form these salts, and write the overall neutralization reaction in both complete and net ionic form. (a) \(\mathrm{NaNO}_{2}\) (b) \(\mathrm{CaSO}_{4}\) (c) NaI (d) \(\mathrm{Mg}_{3}\left(\mathrm{PO}_{4}\right)_{2}\)

Identify the acid and base used to form these salts, and write the overall neutralization reaction in both complete and net ionic form. (a) \(\mathrm{NaCH}_{3} \mathrm{COO}\) (b) \(\mathrm{CaCl}_{2}\) (c) \(\mathrm{LiBr}\) (d) \(\mathrm{Ba}\left(\mathrm{NO}_{3}\right)_{2}\)

Classify each of these exchange reactions as an acid-base reaction, a precipitation reaction, or a gas-forming reaction. Predict the products of the reaction and then balance the completed equation. (a) \(\mathrm{MnCl}_{2}(\mathrm{aq})+\mathrm{Na}_{2} \mathrm{~S}(\mathrm{aq}) \longrightarrow\) (b) \(\mathrm{Na}_{2} \mathrm{CO}_{3}(\mathrm{aq})+\mathrm{ZnCl}_{2}(\mathrm{aq}) \longrightarrow\) (c) \(\mathrm{K}_{2} \mathrm{CO}_{3}(\mathrm{aq})+\mathrm{HClO}_{4}(\mathrm{aq}) \longrightarrow\)

Classify each of these exchange reactions as an acid-base reaction, a precipitation reaction, or a gas-forming reaction. Predict the products of the reaction and then balance the completed equation. (a) \(\mathrm{Fe}(\mathrm{OH})_{3}(\mathrm{~s})+\mathrm{HNO}_{3}(\mathrm{aq}) \longrightarrow\) (b) \(\mathrm{FeCO}_{3}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow\) (c) \(\mathrm{FeCl}_{2}(\mathrm{aq})+\left(\mathrm{NH}_{4}\right)_{2} \mathrm{~S}(\mathrm{aq}) \longrightarrow\) (d) \(\mathrm{Fe}\left(\mathrm{NO}_{3}\right)_{2}(\mathrm{aq})+\mathrm{Na}_{2} \mathrm{CO}_{3}(\mathrm{aq}) \longrightarrow\)

The beautiful mineral rhodochrosite is manganese(II) carbonate. Write an overall balanced equation for the reaction of the mineral with hydrochloric acid. Name each reactant and product.

Identify each substance as a strong electrolyte, weak electrolyte, or nonelectrolyte. (a) \(\mathrm{Na}_{2} \mathrm{CO}_{3}\) (b) \(\mathrm{H}_{2} \mathrm{CO}_{3}\) (c) \(\mathrm{HNO}_{3}\) (d) \(\mathrm{KOH}\)

Identify each substance as a strong electrolyte, weak electrolyte, or nonelectrolyte. (a) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (b) \(\mathrm{HCOOH}\) (c) \(\mathrm{NH}_{3}\) (d) HI

Determine the oxidation number of \(\mathrm{Cl}\) in each formula. (a) \(\mathrm{HCl}\) (b) \(\mathrm{HClO}\) (c) \(\mathrm{HClO}_{2}\) (d) \(\mathrm{HClO}_{3}\) (e) \(\mathrm{HClO}_{4}\)

Determine the oxidation number of \(\mathrm{Mn}\) in each of thes species. (a) \(\left(\mathrm{MnF}_{6}\right)^{3-}\) (b) \(\mathrm{Mn}_{2} \mathrm{O}_{7}\) (c) \(\mathrm{MnO}_{4}^{-}\) (d) \(\mathrm{Mn}(\mathrm{CN})_{6}^{-}\) (e) \(\mathrm{MnO}_{2}\)

Sulfur can exist in many oxidation states. Determine the oxidation state of \(\mathrm{S}\) in each species. (a) \(\mathrm{H}_{2} \mathrm{~S}\) (b) \(\mathrm{S}_{8}\) (c) \(\mathrm{SCl}_{2}\) (d) \(\mathrm{SO}_{3}^{2-}\) (e) \(\mathrm{K}_{2} \mathrm{SO}\)

Classify each reaction as oxidation-reduction, acid-base, or precipitation. (a) \(\mathrm{CdCl}_{2}(\mathrm{aq})+\mathrm{Na}_{2} \mathrm{~S}(\mathrm{aq}) \longrightarrow \mathrm{CdS}(\mathrm{s})+2 \mathrm{NaCl}(\mathrm{aq})\) (b) \(2 \mathrm{Ca}(\mathrm{s})+\mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{CaO}(\mathrm{s})\) (c) \(\mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{~s})+2 \mathrm{HCl}(\mathrm{aq}) \longrightarrow \mathrm{CaCl}_{2}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\ell)\)

Classify each reaction as oxidation-reduction, acid-base, or precipitation. (a) \(\mathrm{Zn}(\mathrm{s})+2 \mathrm{NO}_{3}^{-}(\mathrm{aq})+4 \mathrm{H}^{+}(\mathrm{aq}) \longrightarrow\) $$\mathrm{Zn}^{2+}(\mathrm{aq})+2 \mathrm{NO}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\ell)$$ (b) \(\mathrm{Zn}(\mathrm{OH})_{2}(\mathrm{~s})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow \mathrm{ZnSO}_{4}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\ell)\) (c) \(\mathrm{Ca}(\mathrm{s})+2 \mathrm{H}_{2} \mathrm{O}(\ell) \longrightarrow \mathrm{Ca}(\mathrm{OH})_{2}(\mathrm{~s})+\mathrm{H}_{2}(\mathrm{~g})\)

Identify the region of the periodic table where the elements are good reducing agents. Identify the region where the elements are good oxidizing agents.

Which substances are oxidizing agents? (a) \(\mathrm{Zn}\) (b) \(\mathrm{O}_{2}\) (c) \(\mathrm{HNO}_{3}\) (d) \(\mathrm{MnO}_{4}^{-}\) (e) \(\mathrm{H}_{2}\) (f) \(\mathrm{H}^{+}\)

Which substances are reducing agents? (a) \(\mathrm{Ca}\) (b) \(\mathrm{Ca}^{2+}\) (c) \(\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}\) (d) \(\mathrm{Al}\) (e) \(\mathrm{Br}_{2}\) (f) \(\mathrm{H}_{2}\)

(a) In what groups of the periodic table are the most reactive metals found? Where do we find the least reactive metals? (b) Silver (Ag) does not react with 1-M HCl solution. Will Ag react with a solution of aluminum nitrate, \(\mathrm{Al}\left(\mathrm{NO}_{3}\right)_{3} ?\) If so, write a chemical equation for the reaction. (c) Lead (Pb) will react very slowly with 1-M HCl solution. Aluminum will react with lead(II) sulfate solution, \(\mathrm{PbSO}_{4}\). Will Pb react with an \(\mathrm{AgNO}_{3}\) solution? If so, write a chemical equation for the reaction. (d) On the basis of the information obtained in answering parts (a), (b), and (c), arrange \(\mathrm{Ag}, \mathrm{Al}\), and \(\mathrm{Pb}\) in decreasing order of reactivity.

Nitrogen monoxide is oxidized in air to give brown nitrogen dioxide. $$2 \mathrm{NO}(\mathrm{g})+\mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{NO}_{2}(\mathrm{~g})$$ Starting with \(2.2 \mathrm{~mol} \mathrm{NO},\) calculate how many moles and how many grams of \(\mathrm{O}_{2}\) are required for complete reaction. Calculate what mass of \(\mathrm{NO}_{2}\), in grams, is produced.

Aluminum reacts with oxygen to give aluminum oxide. $$4 \mathrm{Al}(\mathrm{s})+3 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow 2 \mathrm{Al}_{2} \mathrm{O}_{3(\mathrm{~s})$$ If you have \(6.0 \mathrm{~mol} \mathrm{Al},\) calculate the amount (mol) and mass (g) of \(\mathrm{O}_{2}\) needed for complete reaction. Calculate the mass of \(\mathrm{Al}_{2} \mathrm{O}_{3},\) in grams, that is produced.

Iron reacts with oxygen to give iron(III) oxide, \(\mathrm{Fe}_{2} \mathrm{O}_{3}\). (a) Write a balanced equation for this reaction. (b) An ordinary iron nail (assumed to be pure iron) has a mass of \(5.58 \mathrm{~g} ;\) calculate the mass (in grams) of \(\mathrm{Fe}_{2} \mathrm{O}_{3}\) that is produced when the nail is converted completely to \(\mathrm{Fe}_{2} \mathrm{O}_{3}\) (c) Calculate the mass of \(\mathrm{O}_{2}\) (in grams) required for the reaction.

Nitroglycerin decomposes violently according to the equation $$4 \mathrm{C}_{3} \mathrm{H}_{5}\left(\mathrm{NO}_{3}\right)_{3}(\ell) \longrightarrow$$ \(12 \mathrm{CO}_{2}(\mathrm{~g})+10 \mathrm{H}_{2} \mathrm{O}(\ell)+6 \mathrm{~N}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g})\) Calculate the mass (in grams) of each gaseous product produced from \(1.00 \mathrm{~g}\) nitroglycerin.

In making iron from iron ore, this reaction occurs. $$\mathrm{Fe}_{2} \mathrm{O}_{3}(\mathrm{~s})+3 \mathrm{CO}(\mathrm{g}) \longrightarrow 2 \mathrm{Fe}(\mathrm{s})+3 \mathrm{CO}_{2}(\mathrm{~g}) $$ (a) Calculate the mass of iron (in grams) that can be obtained from \(1.00 \mathrm{~kg}\) iron(III) oxide. (b) Calculate the mass of CO required.

Cisplatin, \(\mathrm{Pt}\left(\mathrm{NH}_{3}\right)_{2} \mathrm{Cl}_{2}\), a drug used in the treatment of cancer, can be made by the reaction of \(\mathrm{K}_{2} \mathrm{PtCl}_{4}\) with ammonia, \(\mathrm{NH}_{3}\). Besides cisplatin, the other product is \(\mathrm{KCl}\) (a) Write a balanced equation for this reaction. (b) To obtain \(2.50 \mathrm{~g}\) cisplatin, calculate what masses (in grams) of \(\mathrm{K}_{2} \mathrm{PtCl}_{4}\) and ammonia you need.

Aluminum chloride, \(\mathrm{Al}_{2} \mathrm{Cl}_{6}\), is an inexpensive reagent used in many industrial processes. It is made by treating scrap aluminum with chlorine according to the balanced equation $$2 \mathrm{Al}(\mathrm{s})+3 \mathrm{Cl}_{2}(\mathrm{~g}) \longrightarrow \mathrm{Al}_{2} \mathrm{Cl}_{6}(\mathrm{~s})$$ (a) Determine which reactant is limiting if \(2.70 \mathrm{~g} \mathrm{Al}\) and \(4.05 \mathrm{~g} \mathrm{Cl}_{2}\) are mixed. (b) Calculate what mass of \(\mathrm{Al}_{2} \mathrm{Cl}_{6}\) can be produced. (c) Calculate what mass of the excess reactant remains when the reaction is complete.