Chapter 6

Reaction, \(2 \mathrm{Br}^{-}{ }_{(\mathrm{aq})}+\mathrm{Cl}_{2}(\mathrm{aq}) \longrightarrow 2 \mathrm{Cl}^{-}_{(\mathrm{aq} .)}+\mathrm{Br}_{2(\mathrm{aq} .)}\), is used for commercial preparation of bromine from its salts. Suppose we have \(50 \mathrm{~mL}\) of a \(0.060 \mathrm{M}\) solution of NaBr. What volume of a \(0.050 \mathrm{M}\) solution of \(\mathrm{Cl}_{2}\) is needed to react completely with the Br?

\(\mathrm{Mn}^{2+}(\) aq \()\) can be determined by titration with \(\mathrm{MnO}_{4}^{-}(\) aq \()\) $$ 3 \mathrm{Mn}^{2+}+2 \mathrm{MnO}_{4}^{-} \longrightarrow 6 \mathrm{MnO}_{2}+2 \mathrm{H}_{2} \mathrm{O} $$ A \(25.00 \mathrm{~mL}\) sample of \(\mathrm{Mn}^{2+}\) (aq) requires \(34.77 \mathrm{~mL}\) of \(0.05876 M\) \(\mathrm{KMnO}_{4}\) (aq) for its titration. What is the molarity of the \(\mathrm{Mn}^{2+}\) (aq)?

A \(1.100 \mathrm{~g}\) sample of copper ore is dissolved and the \(\mathrm{Cu}^{2+}(\mathrm{aq})\) is treated with excess \(\mathrm{KI}\). The liberated \(\mathrm{I}_{2}\) requires \(12.12 \mathrm{~mL}\) of \(0.10 \mathrm{M} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\) solution for titration. What is \(\%\) copper by mass in the ore?

A particular acid-rain water has \(\mathrm{SO}_{3}{ }^{2-}\). If a \(25.00 \mathrm{~mL}\) sample of this water requires \(34.08 \mathrm{~mL}\) of \(0.01964 \mathrm{M} \mathrm{KMnO}_{4}\) for its titration, what is the molarity of \(\mathrm{SO}_{3}{ }^{2-}\) in acid-rain? \(2 \mathrm{MnO}_{4}^{-}+5 \mathrm{SO}_{3}^{2-}+6 \mathrm{H}^{+} \longrightarrow 5 \mathrm{SO}_{4}^{2-}+2 \mathrm{Mn}^{2+}+3 \mathrm{H}_{2} \mathrm{O}\)

\(25 \mathrm{~mL}\) of \(0.017 \mathrm{H}_{2} \mathrm{SO}_{3}\) in strongly acidic medium required \(16.9 \mathrm{~mL}\) of \(0.01 \mathrm{M} \mathrm{KMnO}_{4}\) and in neutral medium required \(28.6 \mathrm{~mL}\) of \(0.01 M\) \(\mathrm{KMnO}_{4}\) for complete conversion of \(\mathrm{SO}_{3}{ }^{2-}\) to \(\mathrm{SO}_{4}^{2-}\). Assign the oxidation no. of Mn in the product formed in each case.