Chloride, forms complex ions with many metals. Rather than making the oxalate co
ID: 1029615 • Letter: C
Question
Chloride, forms complex ions with many metals. Rather than making the oxalate compound that you did this quarter, you could have prepared an iron chloride complex replacing the water ligands with chloride. The general formula for an iron (III) chloride complex ion is (a) Iron predominantly forms complexes with 6 ligands. Considering this, what stoichiometric situation would lead to a neutral chloride complex rather than an ion? (b) For your answer in (a), what weight of complex contains one mole of chloride (c) Explain why there is only one condition that satisfies part (a).Explanation / Answer
(a) The oxidation state of iron (III) in the complex is +3. The complex is electrically neutral, i.e, y = 0. The charge on a chloride ion is -1, i.e, the chloride ion is Cl-. The charge on a molecule of water, H2O is 0. Since the complex is neutral we must have three Cl- ions to balance the charge on Fe3+.
The co-ordination number of iron is 6, i.e, six ligands can be accommodated around the iron atom/ion in the complex. Since, we already have 3 Cl- ions in the complex (that counts as co-ordination number 3), hence, the number of H2O molecules will be 3. Therefore, the chemical formula for the complex is [FeCl3.3H2O].
(b) The molar mass of chloride ion is 35.453 g/mol.
1 mole of the complex contains three moles of chloride ions. Hence, one mole of chloride ion is present in 1/3 mole of the complex.
Molar mass of [FeCl3.3H2O] = [1*55.845 + 3*35.453 + 3*(2*1.008 + 1*15.999)] g/mol = 216.249 g/mol.
Mass of the complex corresponding to one mole of chloride ion = (1/3 mole)*(216.249 g/mol) = 72.083 g (ans).
(c) There is only one stoichiometric situation for which the charge on the complex is zero. This is due to the fact that the charges on both iron and chloride ions are fixed integers and only for a particular ratio of iron:chloride ions, the charges on the two ions balance each other and lead to a neutral complex.
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