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27 9. Chromatography. The essence of the method. Classification of chromato- graphic methods of analysis 1) on the aggregate state; 2) on the mechanism of separation of the mixture of substances; 3) on the technique of analysis Input test control on the topic «Surface phenomena. Adsorption» Homework exercises. 1. Give surface tension isotherms for aqueous solutions of the following substances: sulfuric acid, propionic acid, valeric acid, glucose. Explain why iso- therms look like this. How many times does the surface activity of propionic and valeric acids differ? 2. Using the Gibbs equation, calculate the adsorption of ethyl alcohol from aqueous solution, if at 18 °C the surface tension of 0.1 M solution is 39.6×10 –3 j/m  2 , and the surface tension of water 75×10 –3 j/m  2 . Answer: 1,46×10 –5 mol/m  2 . 3. The following data were obtained from the aqueous solution during the adsorption of surface active substance on the porous adsorbent: C, mmol/l 6  25  53 G, mmol/g 0,44  0,72  1 Build the adsorption isotherm, determine graphically the constants in the equation Freundlich. 4. 2 g of activated carbon was placed in 80 ml of a 0.1 M acetic acid solution. After the adsorption equilibrium was established, the solution was filtered. The titration of 10 ml of the filtrate requires 12 ml of a 0.03 M solution of potassium hydroxide KOH. Determine the adsorption of acetic acid in mmol/g. Answer: 2.56 mmol/g 5. Calculate the adsorption of cholesterol from blood plasmausingthe equation of langmure, if the content of cholesterol in the plasma 4,6×10 –5 mol/l, constant k = 20, the value of the maximum adsorption is 9.2×10 –7 mol/m  2. Answer : 2,1×10 –12 mol/m  2. 6. Draw the layout of the molecules of propanol in the surface layer at the boundary of 1) clay-benzene; 2) soot-water. How will the isotherms of adsorption of propanol and hexanol be placed in the first and second cases? 7. A solution containing Fe  2+ ions, was passed through a column of cation exchanger in H + –form. Titration of the filtrate consumed 4 ml of a 1 M solution of potassium hydroxide. Calculate the mass of Fe  2+ ions in the initial solution. Answer : 0.112 g