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9 2. Colligative properties of solutions of electrolytes. Isotonic coefficient. 3. Ebullioscopy and cryoscopy. 4. Study of the colligative properties of biological fluids as important char- acteristics of the state of the organism. The role of osmotic pressure in biologi- cal systems. 5. Isotonic, hyper- and hypotonic solutions and their application in medicine. 6. Osmolality and osmolarity of biological fluids. The output test-control on the themes «Buffer systems» and «Colligative properties». Homework exercises. 1. Calculate the vapor pressure of water over a solution containing 45 g of glucose (C 6 H 12 O 6 ) in 720 ml of water at 25  0 C. The water vapor pressure at 25 °C is 3168 Pa. Answer : 3148 Pa. 2. Determine the molar mass of the non-electrolyte if its mass fraction in the solution is 1.96% and the solution freezes at –0.2480 °C. Answer : 150.4 g/mol. 3. Calculate the freezing temperature of an aqueous solution of ribose (C 5 H 10 O 5 ) with a mass fraction of 2%. Answer : –0.253 0 С. 4. Calculate the osmotic pressure at 310 K of the 20% aqueous solution of glucose (ρ = 1.08 g/ml). What is this solution in comparison with blood: isotonic, hypertonic or hypotonic? (π osm of blood 740–780 kPa)? Answer : 3091.3 kPa, hypertonic. 5. A solution obtained by dissolving 10.11 g of potassium nitrate in distilled water weighing 246 g boils at 100.40 °C. Calculate the isotonic coefficient of potassium nitrate in this solution. Answer : 1,9. 6. Prove that 0.9% NaCl solution (ρ = 1.005 g/ml) is isotonic to blood. 7. The solution contains 6.33 g of the hematin in 100 ml. The osmotic pressure of this solution is 243.4 kPa at 20 °C. Determine the molar mass of hematin. Answer : 633.2 g/mol. Laboratory work: Determination of the molecular weight of non-electrolyte (urea). Calculate the molecular mass of the solute according to Raoul’s formula: ∆t freezing = K k ×b (X), where b (X) is the molality of solution. Determination of the molecular weight by the cryometric method is reduced to the determination of freezing point ∆t. Pour 1 ml of solution in the test tube