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Magazine Problem 4
Why are standard solutions of reductants less often used for titrations than standard solutions of oxidants?
Problem 5
Why are \(\mathrm{Ce}^{4+}\) solutions never used for the titration of reductants in basic solutions?
Problem 6
Why are \(\mathrm{KMnO}_{4}\) solutions filtered before they are standardized?
Problem 7
Why are solutions of \(\mathrm{KMnO}_{4}\) and \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\) generally stored in dark reagent bottles?
Problem 8
What is the primary use of standard \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) solutions?
Problem 10
Suggest a way in which a solution of \(\mathrm{KIO}_{3}\) could be used as a source of known quantities of \(\mathrm{I}_{2}\).
Problem 12
In the titration of \(\mathrm{I}_{2}\) solutions with \(\mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\), the starch indicator is never added until just before chemical equivalence. Why?
Problem 14
How would you prepare \(1.000 \mathrm{~L}\) of \(0.05000 \mathrm{M}\) \(\mathrm{KBrO}_{3}\) ?
Problem 18
Calculate the percentage of \(\mathrm{MnO}_{2}\) in a mineral specimen if the \(\mathrm{I}_{2}\) liberated by a \(0.1267-\mathrm{g}\) sample in the net reaction $$ \mathrm{MnO}_{2}(s)+4 \mathrm{H}^{+}+2 \mathrm{I}^{-} \rightarrow \mathrm{Mn}^{2+}+\mathrm{I}_{2}+2 \mathrm{H}_{2} \mathrm{O} $$ required \(29.62 \mathrm{~mL}\) of \(0.08041 \mathrm{M} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}\).
Problem 19
A 0.7120-g specimen of iron ore was dissolved and passed through a Jones reductor. Titration of the \(\mathrm{Fe}\) (II) produced required \(41.63 \mathrm{~mL}\) of \(0.01926 \mathrm{M}\) \(\mathrm{KMnO}_{4}\). Express the results of this analysis in terms of (a) percent Fe and (b) percent \(\mathrm{Fe}_{2} \mathrm{O}_{3}\).
