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# A10 Heavy Metals – Environmental Impact

1. Heavy metals can be present in water supplies and can be highly toxic. i. Why are high doses of these metals toxic? ii. Suggest and briefly explain three different methods in which heavy metals can be removed from polluted water supplies.
2. EDTA is a molecule which is a source of the polydentate ligand
$\textsf{EDTA}{^\textsf{4-}}$
i. Explain how polydentate ligands form complexes with heavy metal atoms. ii. Complete the following equation:
$\textsf{Ni(H}_\textsf2\textsf{O)}_\textsf{6}{^\textsf{2+}}\textsf{ + EDTA}{^\textsf{4-}}$
iii. Explain, in terms of entropy changes, why the formation of an EDTA chelate is favourable in equations like the example in part ii.
3. i. Write down the formula of ethane-1,2-diamine. ii. Why is this molecule able to act as a ligand? iii. Explain how many coordinate bonds one molecule of this compound can form with a heavy metal ion. iv. Write the formula of the complex formed between this molecule and an ion of
$\textsf{ Co}{^\textsf{2+}}$
4. Calculate the solubility of
$\textsf{CaSO}_\textsf4$
in
$\textsf{g dm}^\textsf{-3}$
in pure water if Ksp =
$\textsf{4.93}\times\textsf{10}^\textsf{-5}$
5. Calculate the maximum solubility of
$\textsf{CaSO}_\textsf4$
in
$\textsf{g dm}^\textsf{-3}$
$\textsf{ 0.5 mol dm}^\textsf{-3}$
solution of
$\textsf{H}_\textsf2\textsf{SO}_\textsf4$