Ch.21 - Transition Elements and Coordination Chemistry
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- In acidic aqueous solution, the complex trans-[Co(en)2Cl2]+ undergoes the following substitution reaction:
Problem 138
The reaction is first order in trans-[Co(en)2Cl2]+, and the rate constant at 25 °C is 3.2 × 10⁻⁵ s⁻¹. (a) What is the half-life of the reaction in hours? (b) If the initial concentration of trans-[Co(en)2Cl2]+ is 0.138 M, what is its molarity after a reaction time of 16.5 h? (c) Devise a possible reaction mechanism with a unimolecular rate-determining step. - Chromium forms three isomeric compounds A, B, and C with percent composition 19.52% Cr, 39.91% Cl, and 40.57% H2O. When a sample of each compound was dissolved in water and aqueous AgNO3 was added, a precipitate of AgCl formed immediately. A 0.225-g sample of compound A gave 0.363 g of AgCl, 0.263 g of B gave 0.283 g of AgCl, and 0.358 g of C gave 0.193 g of AgCl. One of the three compounds is violet, while the other two are green. In all three, chromium has a coordination number of 6. (a) What are the empirical formulas of A, B, and C? (b) What are the probable structural formulas of A, B, and C? Draw the structure of the cation in each compound. Which cation can exist as diastereoisomers? (c) What are the approximate freezing points of 0.25 m solutions of A, B, and C, assuming complete dissociation?
Problem 139