475

19 4. Calculate the concentration of Co  3+ ions in a 0.1 M solution of [Co (NH3) 6 ] Cl 3. K inst. = 6,17×10 –36. Answer : 1,446×10 –6 mol/l. 5. Calculate the molarity of Cd  2+ ions in 1 liter of a 0.01 M solution of K 2 [Cd (CN) 4 ], in which 1 mole KCN is additionally dissolved. (K inst [Cd (CN) 4 ]  2– = 1.4×10 –19 ). Answer : 1,4×10 –21 mol/l. 6. Calculate the instability constant of the complex ion [Cu (CN) 2 ]  – if at 25  0 C the Gibbs energy change is 137 kJ/mol. Answer : 9,41×10 –24. 7. 0.1 mol of KCN was further dissolved in 1 liter of a 0.05 M solution of K 2 [Cd (CN) 4 ]. What is the molarity of the sulfide ions, which leads to the precipitation of CdS from this dissolution? K S (CdS)= 3.6×10 –29 ; K inst . ([Cd (CN) 4 ]  2– ) = 1.4×10 –17. Answer : 5,14×10 –15. 8. Write the structure of the Trilon B complex with: a) Cu  2+ ; b) Co  3+ ; c) Pt  4+ if it is known that Trilon B forms a complex of composition 1: 1 (in moles) with ions of these metals. Questions for self-study. 1. The idea of ​the concrements formed in the body, their types, approximate composition. 2. Representations on the structure of metalloenzymes and other biocomplex compounds. Laboratory work Experience 1. Trilonometric determination of the total hardness of water H (H 2 O) The total hardness of water is due to the presence of dissolved calcium and magnesium salts and is expressed by the total content of Ca  2+ and Mg  2+ ions in mmol per liter of water. 100 ml of water pour to the flask using a graduated cylinder, 5 ml of am- monia buffer solution is added, a small amount of the crystal indicator of the black ichorochrom T. The mixture is titrated with a solution of Trilon B to the transition of the wine red color to blue. The titration ends at the moment when from one drop of Trilon B solution the violet color turns blue. Titration is re- peated twice. The total hardness of water (number of Ca 2+ and Mg2+ ions) is 2 2 (Tr B) (Tr B) (H O)= 1000 (H O) eq C V H V ⋅ ⋅ , mmol/l where C eq (Tr B) – normality of the Trilon B solution, mol/l; V (Tr B) – volume of the Trilon B solution, consumed for titration, ml; V (H 2 O) – volume of water, which underwent the analysis, ml.