Sergey Bylikin, Gary Horner and, Brian Murphy Solutions for Chapter: Materials, Exercise 17: Questions

Hydroxyl free-radicals can be generated naturally in the body. This process is catalysed by iron in the following two steps:

Reaction 1: ${\mathrm{Fe}}^{3+}+·{{\mathrm{O}}_2}^{-}\to {\mathrm{Fe}}^{2+}+{\mathrm{O}}_2$.
Reaction 2: ${\mathrm{Fe}}^{2+}+{\mathrm{H}}_2{\mathrm{O}}_2\to {\mathrm{Fe}}^{3+}+·\mathrm{OH}+{\mathrm{OH}}^{-}$.

Deduce whether iron is acting as a heterogeneous or homogeneous catalyst and justify your answer.

Hydroxyl free-radicals can be generated naturally in the body. This process is catalysed by iron in the following two steps:

Reaction 1: ${\mathrm{Fe}}^{3+}+·{{\mathrm{O}}_2}^{-}\to {\mathrm{Fe}}^{2+}+{{\mathrm{O}}_2}^{-}$.
Reaction 2: ${\mathrm{Fe}}^{2+}+{\mathrm{H}}_2{\mathrm{O}}_2\to {\mathrm{Fe}}^{3+}+·\mathrm{OH}+\mathrm{OH}$.

Show that reactions 1 and 2 are redox equations by writing the oxidation half-equation and the reduction half-equation for each.

Heavy metals are often removed from solutions by precipitation. Use the Data booklet to calculate the concentration of sulphuric acid necessary to precipitate mercury($\mathrm{I}$) ions at a concentration of $3 \mathrm{\mu mol} {\mathrm{dm}}^{-3}$? [${\mathrm{Hg}}_2{\mathrm{SO}}_4, {\mathrm{K}}_{\mathrm{sp}}=6.5\times {10}^{-7}$].

Heavy metals are often removed from solutions by precipitation. Evaluate the effectiveness of this method for mercury removal and suggest improvements.

Heavy metals are often removed from solutions by precipitation. Magnesium ion concentrations can be determined by precipitation as magnesium hydroxide. Given that the solubility product, ${\mathrm{K}}_{\mathrm{sp}}$ of magnesium hydroxide is $1.20\times {10}^{-11}$. Calculate the concentration, in $\mathrm{mol} {\mathrm{dm}}^{-3}$ of magnesium ions required to form a precipitate in a solution where the final hydroxide ion concentration is $2.00 \mathrm{mol} {\mathrm{dm}}^{-3}$?

Chromium($\mathrm{III}$) ions form a hexa-aqua complex ion, $\left[\mathrm{Cr}{\left({\mathrm{H}}_2\mathrm{O}\right)}_6\right){]}^{3+}\left(\mathrm{aq}\right)$. Write a balanced equation for the reaction of this complex with ${\mathrm{EDTA}}^{4-}\left(\mathrm{aq}\right)$ and explain why $\mathrm{EDTA}$ will replace the water in the complex ion.

Explain the difference between precipitation, chelation, and adsorption as methods of removing heavy metal contamination.

Use the Data booklet to calculate the molar solubility of zinc at $\mathrm{pH} 11$ and explain why zinc ions are more soluble in acidic solutions.