The Advanced Placement Examination in Chemistry s3
The Advanced Placement Examination in Chemistry
Part II - Free Response Questions & Answers
1970 to 2007
Ligands
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Ligands page 3
1972
EXPERIMENTAL MEASUREMENTS
COMPOUND / Moles of Chloride Precipitated by AgNO3 per mole CrCl3.6H2O / Moles of Water Removed by drying agent per mole of CrCl3.6H2O / Number of ions per “molecule” of complex (from electrical conductivity)Violet / 3 / 0 / 4
Light Green / 2 / 1 / 3
Dark Green / 1 / 2 / 2
For each of the three compounds having the same formula, CrCl3.6H2O, account for the experimental measurements given above. Show the structural formula for each of the compounds, and relate the structure to the measurements.
1983 C
The transition metal complex ion, [Co(NH2CH2CH2NH2)2Cl2]+, has an octahedral shape and exists as two geometrical isomers.
(a) Draw the structural formulas for the two geometrical isomers.
(b) One of the geometrical isomers exists as two optical isomers. Draw the structural formulas for the two optical isomers.
(c) How many moles of AgCl would be immediately precipitated when excess AgNO3 solution is added to an aqueous solution contain 1 mole of [Co(NH2CH2CH2NH2)2Cl2]Cl, the chloride salt of the transition metal complex? Explain your reasoning.
Answer:
(a) Representation of the cobalt complex as an octahedral complex.
Ethylenediamine shown as a bidentate ligand.
Representation of the cis isomer.
Representation of the trans isomer.
(b) The cis isomer has optical isomers.
Showing structures for the optical pair.
(c) One mole of AgCl precipitates. One chloride is shown as ionically bonded and precipitates as AgCl at once.
Each of the other chlorides shares a pair of electrons with the cobalt and thus does not readily form an AgCl precipitate.
N.B., This topic is no longer listed as part of the A.P. Chemistry Syllabus.
Copyright ⌐ 1972 to 1983 by Educational Testing Service, Princeton, NJ 08541. All rights reserved. For face-to-face teaching purposes, classroom teachers are permitted to reproduce the questions. Portions copyright ⌐ 1993-94 Unlimited Potential, Framingham, MA 01701-2619.