Chapter 12

Impure phosphoric acid for use in the manufacture of fertilizers is produced by the reaction of sulfuric acid on phosphate rock, of which a principal component is \(\mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)\). The reaction is $$ \begin{aligned} \mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}(\mathrm{~s}) &+3 \mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \longrightarrow \\ & 3 \mathrm{CaSO}_{4}(\mathrm{~s})+2 \mathrm{H}_{3} \mathrm{PO}_{4}(\mathrm{aq}) \end{aligned} $$ (a) How many moles of \(\mathrm{H}_{3} \mathrm{PO}_{4}\) can be produced from the reaction of \(200 \mathrm{~kg}\) of \(\mathrm{H}_{2} \mathrm{SO}_{4}\) ? (b) Determine the mass of calcium sulfate that is produced as a by. product of the reaction of \(200 \mathrm{~mol} \mathrm{Ca}_{3}\left(\mathrm{PO}_{4}\right)_{2}\).

\(\mathbf{L} .4\) The compound diborane, \(\mathrm{B}_{2} \mathrm{H}_{6}\), was at one time considered for use as a rocket fuel. Its combustion reaction is $$ \mathrm{B}_{2} \mathrm{H}_{6}(\mathrm{~g})+3 \mathrm{O}_{2}(\mathrm{l}) \rightarrow 2 \mathrm{HBO}_{2}(\mathrm{~g})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) $$ The fact that \(\mathrm{HBO}_{2}\), a reactive compound, was produced rather than the relatively inert \(\mathrm{B}_{2} \mathrm{O}_{3}\) was a factor in the discontinuation of the investigation of diborane as a fuel. (a) What mass of liquid oxygen (LOX) would be needed to burn \(50.0 \mathrm{~g}\) of \(\mathrm{B}_{2} \mathrm{H}_{6}\) ? (b) Determine the mass of \(\mathrm{HBO}_{2}\) produced from the combustion of \(30.0 \mathrm{~g}\) of \(\mathrm{B}_{2} \mathrm{H}_{6}\).

Potassium superoxide, \(\mathrm{KO}_{2}\), is utilized in closedsystem breathing apparatus to remove carbon dioxide and water from exhaled air. The removal of water generates oxygen for breathing by the reaction $$ 4 \mathrm{KO}_{2}(\mathrm{~s})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \longrightarrow 3 \mathrm{O}_{2}(\mathrm{~g})+4 \mathrm{KOH}(\mathrm{s}) $$ The potassium hydroxide removes carbon dioxide from the apparatus by the reaction $$ \mathrm{KOH}(\mathrm{s})+\mathrm{CO}_{2}(\mathrm{~g}) \longrightarrow \mathrm{KHCO}_{3}(\mathrm{~s}) $$ (a) What mass of potassium superoxide generates \(20.0 \mathrm{~g}\) of \(\mathrm{O}_{2}\) ? (b) What mass of \(\mathrm{CO}_{2}\) can be removed from the apparatus by \(100 \mathrm{~g}\) of \(\mathrm{KO}_{2}\) ?

When a hydrocarbon burns, water is produced as well as carbon dioxide. (For this reason, clouds of condensed water droplets are often seen coming from automobile exhausts, especially on a cold day.) The density of gasoline is \(0.79 \mathrm{~g} \cdot \mathrm{mL}^{-1}\). Assume gasoline to be represented by octane, \(\mathrm{C}_{8} \mathrm{H}_{18}\), for which the combustion reaction is $$ \begin{aligned} 2 \mathrm{C}_{\mathrm{g}} \mathrm{H}_{18}(\mathrm{l}) &+25 \mathrm{O}_{2}(\mathrm{~g}) \longrightarrow \\ & 16 \mathrm{CO}_{2}(\mathrm{~g})+18 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \end{aligned} $$ Calculate the mass of water produced from the combustion of \(1.0 \mathrm{~L}\) of gasoline.

A 15.00-mL. sample of sodium hydroxide was titrated to the stoichiometric point with \(17.40 \mathrm{~mL}\). of \(0.234 \mathrm{M} \mathrm{HCl}(\mathrm{aq})\). (a) What is the initial molarity of \(\mathrm{NaOH}\) in the solution? (b) Calculate the mass of \(\mathrm{NaOH}\) in the solution.

A 15.00-mL. sample of oxalic acid, \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}\) (with two acidic protons), was titrated to the stoichiometric point with \(17.02 \mathrm{~mL}\) of \(0.288 \mathrm{M} \mathrm{NaOH}(a q)\). (a) What is the molarity of the oxalic acid? (b) Dctermine the mass of oxalic acid in the solution.

A 10.0-mL volume of \(3.0 \mathrm{M} \mathrm{KOH}(\mathrm{aq})\) is transferred to a \(250-\mathrm{mL}\) volumetric flask and diluted to the mark. It was found that \(38.5 \mathrm{~mL}\) of this diluted solution was needed to reach the stoichiometric point in a titration of \(10.0 \mathrm{~mL}\) of a phosphoric acid solution according to the reaction $$ \begin{aligned} 3 \mathrm{KOH}(\mathrm{aq})+& \mathrm{H}_{3} \mathrm{PO}_{4}(\mathrm{aq}) \longrightarrow \\ & \mathrm{K}_{3} \mathrm{PO}_{4}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(1) \end{aligned} $$ (a) Calculate the molarity of \(\mathrm{H}_{3} \mathrm{PO}_{4}\) in the solution. (b) What mass of \(\mathrm{H}_{3} \mathrm{PO}_{4}\) is in the initial solution?

In a titration, a \(3.25 \mathrm{~g}\) sample of an acid, HX, requires \(68.8 \mathrm{~mL}\) of a \(0.750 \mathrm{M} \mathrm{NaOH}(\mathrm{aq})\) solution for complete reaction. What is the molar mass of the acid?

In a titration, \(16.02 \mathrm{~mL}\) of \(0.100 \mathrm{M} \mathrm{NaOH}(\mathrm{aq})\) was required to titrate \(0.2011 \mathrm{~g}\) of an unknown acid, \(\mathrm{HX}\). What is the molar mass of the acid?

A vitamin C tablet was analyzed to detcrmine whether it did in fact contain, as the manufacturer claimed, \(1.0 \mathrm{~g}\) of the vitamin. A tablet was dissolved in water to form a \(100.00-\mathrm{mL}\). solution, and a \(10.0-\mathrm{mL}\). sample was titrated with iodine (as potassium triiodide). It required \(10.1 \mathrm{~mL}\) of \(0.0521 \mathrm{MI}_{3}\) (aq) to reach the stoichiometric point in the titration, Given that \(1 \mathrm{~mol} \mathrm{I}_{3}^{-}-1 \mathrm{~mol}\) vitamin \(\mathrm{C}\) in the reaction, is the manufacturer's claim correct? The molar mass of vitamin \(\mathrm{C}\) is \(176 \mathrm{~g} \cdot \mathrm{mol}^{-1}\).