Chapter 4

Write balanced equations for the following reactions in basic solution. (a) \(\mathrm{SO}_{2}(g)+\mathrm{I}_{2}(a q) \longrightarrow \mathrm{SO}_{3}(g)+\mathrm{I}^{-}(a q)\) (b) \(\mathrm{Zn}(s)+\mathrm{NO}_{3}^{-}(a q) \longrightarrow \mathrm{NH}_{3}(a q)+\mathrm{Zn}^{2+}(a q)\) (c) \(\mathrm{ClO}^{-}(a q)+\mathrm{CrO}_{2}^{-}(a q) \longrightarrow \mathrm{Cl}^{-}(a q)+\mathrm{CrO}_{4}^{2-}(a q)\) (d) \(\mathrm{K}(s)+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{K}^{+}(a q)+\mathrm{H}_{2}(g)\)

Write balanced equations for the following reactions in basic solution. (a) \(\mathrm{Ni}(\mathrm{OH})_{2}(s)+\mathrm{N}_{2} \mathrm{H}_{4}(a q) \longrightarrow \mathrm{Ni}(s)+\mathrm{N}_{2}(g)\) (b) \(\mathrm{Fe}(\mathrm{OH})_{3}(s)+\mathrm{Cr}^{3+}(a q) \longrightarrow \mathrm{Fe}(\mathrm{OH})_{2}(s)+\mathrm{CrO}_{4}{\underline{\phantom{xx}}}^{2-}(a q)\) (c) \(\mathrm{MnO}_{4}^{-}(a q)+\mathrm{BrO}_{3}^{-}(a q) \longrightarrow \mathrm{MnO}_{2}(s)+\mathrm{BrO}_{4}^{-}(a q)\) (d) \(\mathrm{H}_{2} \mathrm{O}_{2}(a q)+\mathrm{IO}_{4}^{-}(a q) \longrightarrow \mathrm{IO}_{2}^{-}(a q)+\mathrm{O}_{2}(g)\)

Write balanced net ionic equations for the following reactions in acid solution. (a) Liquid hydrazine reacts with an aqueous solution of sodium bromate. Nitrogen gas and bromide ions are formed. (b) Solid phosphorus \(\left(P_{4}\right)\) reacts with an aqueous solution of nitrate to form nitrogen oxide gas and dihydrogen phosphate \(\left(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\right)\) ions. (c) Aqueous solutions of potassium sulfite and potassium permanganate react. Sulfate and manganese(II) ions are formed.

Write balanced net ionic equations for the following reactions in acid solution. (a) Nitrogen oxide and hydrogen gases react to form ammonia gas and steam. (b) Hydrogen peroxide reacts with an aqueous solution of sodium hypochlorite to form oxygen and chlorine gases. (c) Zinc metal reduces the vanadyl ion \(\left(\mathrm{VO}^{2+}\right)\) to vanadium(III) ions. Zinc ions are also formed.

A solution of potassium permanganate reacts with oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\) to form carbon dioxide and solid manganese(IV) oxide \(\left(\mathrm{MnO}_{2}\right)\). (a) Write a balanced net ionic equation for the reaction. (b) If \(20.0 \mathrm{~mL}\) of \(0.300 M\) potassium permanganate is required to react with \(13.7 \mathrm{~mL}\) of oxalic acid, what is the molarity of the oxalic acid? (c) What is the mass of manganese(IV) oxide formed?

Iodine reacts with thiosulfate ion, \(\mathrm{S}_{2} \mathrm{O}_{3}{\underline{\phantom{xx}}}^{2-}\), to give iodide ion and the tetrathionate ion, \(\mathrm{S}_{4} \mathrm{O}_{6}{\underline{\phantom{xx}}}^{2-}\). (a) Write a balanced net ionic equation for the reaction. (b) If \(25.0 \mathrm{~g}\) of iodine is dissolved in enough water to make \(1.50 \mathrm{~L}\) of solution, what volume of \(0.244 M\) sodium thiosulfate will be needed for complete reaction?

Hydrogen gas is bubbled into a solution of barium hydroxide that has sulfur in it. The unbalanced equation for the reaction that takes place is $$ \mathrm{H}_{2}(g)+\mathrm{S}(s)+\mathrm{OH}^{-}(a q) \longrightarrow \mathrm{S}^{2-}(a q)+\mathrm{H}_{2} \mathrm{O} $$ (a) Balance the equation. (b) What volume of \(0.349 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}\) is required to react completely with \(3.00 \mathrm{~g}\) of sulfur?

Consider the reaction between silver and nitric acid for which the unbalanced equation is $$ \mathrm{Ag}(s)+\mathrm{H}^{+}(a q)+\mathrm{NO}_{3}^{-}(a q) \longrightarrow \mathrm{Ag}^{+}(a q)+\mathrm{NO}_{2}(g)+\mathrm{H}_{2} \mathrm{O} $$ (a) Balance the equation. (b) If \(42.50 \mathrm{~mL}\) of \(12.0 \mathrm{M}\) nitric acid furnishes enough \(\mathrm{H}^{+}\) to react with silver, how many grams of silver react?

Limonite, an ore of iron, is brought into solution in acidic medium and titrated with \(\mathrm{KMnO}_{4}\). The unbalanced equation for the reaction is $$ \mathrm{MnO}_{4}^{-}(a q)+\mathrm{Fe}^{2+}(a q) \longrightarrow \mathrm{Fe}^{3+}(a q)+\mathrm{Mn}^{2+}(a q) $$ It is found that a \(1.000-\mathrm{g}\) sample of the ore requires \(75.52 \mathrm{~mL}\) of \(0.0205 \mathrm{M}\) \(\mathrm{KMnO}_{4}\). What is the percent of Fe in the sample?

Laundry bleach is a solution of sodium hypochlorite (NaClO). To determine the hypochlorite (ClO \(^{-}\) ) content of bleach (which is responsible for its bleaching action), sulfide ion is added in basic solution. The balanced equation for the reaction is $$ \mathrm{ClO}^{-}(a q)+\mathrm{S}^{2-}(a q)+\mathrm{H}_{2} \mathrm{O} \longrightarrow \mathrm{Cl}^{-}(a q)+\mathrm{S}(s)+2 \mathrm{OH}^{-}(a q) $$ The chloride ion resulting from the reduction of HClO is precipitated as \(\mathrm{AgCl}\). When \(50.0 \mathrm{~mL}\) of laundry bleach \(\left(d=1.02 \mathrm{~g} / \mathrm{cm}^{3}\right)\) is treated as described above, \(4.95 \mathrm{~g}\) of \(\mathrm{AgCl}\) is obtained. What is the mass percent of \(\mathrm{NaClO}\) in the bleach?

Laws passed in some states define a drunk driver as one who drives with a blood alcohol level of \(0.10 \%\) by mass or higher. The level of alcohol can be determined by titrating blood plasma with potassium dichromate according to the unbalanced equation $$ \mathrm{H}^{+}(a q)+\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}(a q) \longrightarrow \mathrm{Cr}^{3+}(a q)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O} $$ Assuming that the only substance that reacts with dichromate in blood plasma is alcohol, is a person legally drunk if \(38.94 \mathrm{~mL}\) of \(0.0723 \mathrm{M}\) potassium dichromate is required to titrate a \(50.0\) -g sample of blood plasma?

A sample of limestone weighing \(1.005 \mathrm{~g}\) is dissolved in \(75.00 \mathrm{~mL}\) of \(0.2500 \mathrm{M}\) hydrochloric acid. The following reaction occurs: $$ \mathrm{CaCO}_{3}(s)+2 \mathrm{H}^{+}(a q) \longrightarrow \mathrm{Ca}^{2+}(a q)+\mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O} $$ It is found that \(19.26 \mathrm{~mL}\) of \(0.150 \mathrm{M} \mathrm{NaOH}\) is required to titrate the excess \(\mathrm{HCl}\) left after reaction with the limestone. What is the mass percent of \(\mathrm{CaCO}_{3}\) in the limestone?

The standard set by OSHA for the maximum amount of ammonia permitted in the workplace is \(5.00 \times 10^{-3} \%\) by mass. To determine a factory's compliance, \(10.00 \mathrm{~L}\) of air \((d=1.19 \mathrm{~g} / \mathrm{L})\) is bubbled into \(100.0 \mathrm{~mL}\) of \(0.02500 \mathrm{M} \mathrm{HCl}\) at the same temperature and pressure. Ammonia in the air bubbled in reacts with \(\mathrm{H}^{+}\) as follows: $$ \mathrm{NH}_{3}(a q)+\mathrm{H}^{+}(a q) \longrightarrow \mathrm{NH}_{4}^{+}(a q) $$ The unreacted hydrogen ions required \(57.00 \mathrm{~mL}\) of \(0.03500 \mathrm{M} \mathrm{NaOH}\) for complete neutralization. Is the factory compliant with the OSHA standards for ammonia in the workplace?

Consider the following balanced redox reaction in basic medium. \(3 \mathrm{Sn}^{2+}(a q)+\mathrm{Cr}_{2} \mathrm{O}_{7}^{2-}(a q)+4 \mathrm{H}_{2} \mathrm{O} \longrightarrow\) \(3 \mathrm{Sn}^{4+}(a q)+\mathrm{Cr}_{2} \mathrm{O}_{3}(s)+8 \mathrm{OH}^{-}(a q)\) (a) What is the oxidizing agent? (b) What species has the element that increases its oxidation number? (c) What species contains the element with the highest oxidation number? (d) If the reaction were to take place in acidic medium, what species would not be included in the reaction?

Identify the type of aqueous reaction using the symbols PPT for precipitation, SA/SB for strong acid-strong base, SA/WB for strong acid-weak base, WA/SB for weak acid-strong base, and NR for no reaction. (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}+\mathrm{HCl}\) (b) \(\mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{HF}\) (c) \(\mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{Na}_{3} \mathrm{PO}_{4}\) (d) \(\mathrm{Ag}_{2} \mathrm{SO}_{4}+\mathrm{BaCl}_{2}\) (e) \(\mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}+\mathrm{NaCl}\)

Using circles to represent cations and squares to represent anions, show pictorially the reactions that occur between aqueous solutions of (a) \(\mathrm{Ba}^{2+}\) and \(\mathrm{OH}^{-}\) (b) \(\mathrm{Co}^{3+}\) and \(\mathrm{PO}_{4}^{3-}\)

Using squares to represent atoms of one element (or cations) and circles to represent the atoms of the other element (or anions), represent the principal species in the following pictorially. (You may represent the hydroxide anion as a single circle.) (a) a solution of \(\mathrm{HCl}\) (b) a solution of HF (c) a solution of \(\mathrm{KOH}\) (d) a solution of \(\mathrm{HNO}_{2}\)

A student is asked to identify the metal nitrate present in an aqueous solution. The cation in the solution can either be \(\mathrm{Na}^{+}, \mathrm{Ba}^{2+}, \mathrm{Ag}^{+}\), or \(\mathrm{Ni}^{2+}\). Results of solubility experiments are as follows: unknown + chloride ions-no precipitate unknown + carbonate ions-precipitate unknown + sulfate ions-precipitate What is the cation in the solution?

Use the following reactions to arrange the cations \(\mathrm{W}^{+}, \mathrm{X}^{+}, \mathrm{Y}^{+}\), and \(\mathrm{Z}^{+}\) in order of their increasing ability as oxidizing agents. $$ \begin{aligned} &\mathrm{W}^{+}+\mathrm{Z} \longrightarrow \text { no reaction } \\ &\mathrm{X}^{+}+\mathrm{W} \longrightarrow \text { no reaction } \\ &\mathrm{Y}^{+}+\mathrm{X} \longrightarrow \mathrm{X}^{+}+\mathrm{Y} \\ &\mathrm{Y}^{+}+\mathrm{Z} \longrightarrow \mathrm{Z}^{+}+\mathrm{Y} \end{aligned} $$

Three students titrate different samples of the same solution of \(\mathrm{HCl}\) to obtain its molarity. Below are their data. Student \(\mathrm{A}: \quad 20.00 \mathrm{~mL} \mathrm{HCl}+20.00 \mathrm{~mL} \mathrm{H}_{2} \mathrm{O}\) \(0.100 \mathrm{M} \mathrm{NaOH}\) used to titrate to the equivalence point Student B: \(\quad 20.00 \mathrm{~mL} \mathrm{HCl}+40.00 \mathrm{~mL} \mathrm{H}_{2} \mathrm{O}\) \(0.100 \mathrm{M} \mathrm{NaOH}\) used to titrate to the equivalence point Student C: \(\quad 20.00 \mathrm{~mL} \mathrm{HCl}+20.00 \mathrm{~mL} \mathrm{H}_{2} \mathrm{O}\) \(0.100 \mathrm{M} \mathrm{Ba}(\mathrm{OH})_{2}\) used to titrate to the equivalence point. All the students calculated the molarities correctly. Which (if any) of the following statements are true? (a) The molarity calculated by \(A\) is half that calculated by \(B\). (b) The molarity calculated by \(\mathrm{A}\) is equal to that calculated by \(\mathrm{C}\). (c) The molarity calculated by B is twice that calculated by C. (d) The molarity calculated by \(\mathrm{A}\) is twice that calculated by \(\mathrm{B}\). (e) The molarity calculated by \(\mathrm{A}\) is equal to that calculated by \(\mathrm{B}\). Challenge Problems

Calcium in blood or urine can be determined by precipitation as call cium oxalate, \(\mathrm{CaC}_{2} \mathrm{O}_{4}\). The precipitate is dissolved in strong acid and titrated with potassium permanganate. The products of the reaction are carbon dioxide and manganese(II) ion. A 24-hour urine sample is collected from an adult patient, reduced to a small volume, and titrated with \(26.2 \mathrm{~mL}\) of \(0.0946 \mathrm{M} \mathrm{KMnO}_{4}\). How many grams of calcium oxalate are in the sample? Normal range for \(\mathrm{Ca}^{2+}\) output for an adult is 100 to \(300 \mathrm{mg}\) per 24 hour. Is the sample within the normal range?

Stomach acid is approximately \(0.020 \mathrm{M} \mathrm{HCl}\). What volume of this acid is neutralized by an antacid tablet that weighs \(330 \mathrm{mg}\) and contains \(41.0 \% \mathrm{Mg}(\mathrm{OH})_{2}, 36.2 \% \mathrm{NaHCO}_{3}\), and \(22.8 \% \mathrm{NaCl} ?\) The reactions in- volved are $$ \begin{gathered} \mathrm{Mg}(\mathrm{OH})_{2}(s)+2 \mathrm{H}^{+}(a q) \longrightarrow \mathrm{Mg}^{2+}(a q)+2 \mathrm{H}_{2} \mathrm{O} \\ \mathrm{HCO}_{3}^{-}(a q)+\mathrm{H}^{+}(a q) \longrightarrow \mathrm{CO}_{2}(g)+\mathrm{H}_{2} \mathrm{O} \end{gathered} $$

Copper metal can reduce silver ions to metallic silver. The copper is oxidized to copper ions according to the reaction $$ 2 \mathrm{Ag}^{+}(a q)+\mathrm{Cu}(s) \longrightarrow \mathrm{Cu}^{2+}(a q)+2 \mathrm{Ag}(s) $$ A copper strip with a mass of \(2.00 \mathrm{~g}\) is dipped into a solution of \(\mathrm{AgNO}_{3}\). After some time has elapsed, the copper strip is coated with silver. The strip is removed from the solution, dried, and weighed. The coated strip has a mass of \(4.18 \mathrm{~g}\). What are the masses of copper and silver metals in the strip? (Hint: Remember that the copper metal is being used up as silver metal forms.)

A solution contains both iron(II) and iron(III) ions. A \(50.00-\mathrm{mL}\) sample of the solution is titrated with \(35.0 \mathrm{~mL}\) of \(0.0280 \mathrm{M} \mathrm{KMnO}_{4}\), which oxidizes \(\mathrm{Fe}^{2+}\) to \(\mathrm{Fe}^{3+} .\) The permanganate ion is reduced to manganese(II) ion. Another \(50.00-\mathrm{mL}\) sample of the solution is treated with zinc, which reduces all the \(\mathrm{Fe}^{3+}\) to \(\mathrm{Fe}^{2+}\). The resulting solution is again titrated with \(0.0280 \mathrm{M}\) \(\mathrm{KMnO}_{4} ;\) this time \(48.0 \mathrm{~mL}\) is required. What are the concentrations of \(\mathrm{Fe}^{2+}\) and \(\mathrm{Fe}^{3+}\) in the solution?

I A student is given \(0.930 \mathrm{~g}\) of an unknown acid, which can be either oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\), or citric acid, \(\mathrm{H}_{3} \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{O}_{7}\). To determine which acid she has, she titrates the unknown acid with \(0.615 \mathrm{M} \mathrm{NaOH}\). The equivalence point is reached when \(33.6 \mathrm{~mL}\) are added. What is the unknown acid?

Solid iron(III) hydroxide is added to \(625 \mathrm{~mL}\) of \(0.280 \mathrm{M} \mathrm{HCl}\). The resulting solution is acidic and titrated with \(238.2 \mathrm{~mL}\) of \(0.113 \mathrm{M} \mathrm{NaOH}\). What mass of iron(III) hydroxide was added to the HCl?