475

32 of ferric hydroxide sol from the burette in four clean test tubes, add the neces- sary volume of water. Then add the necessary volume of electrolyte to each tube and mix it immediately. After 10 minutes, note which turbidity is observed in the test tubes. Record the results of the observations in the table («+» or «-»). Calculate the coagulation threshold of the sol and the coagulability for each electrolyte, using the equation: 1000 el el Th sol el С V С V V ⋅ = ⋅ + where C el  is the normality of electrolyte, mol/l; V el  is the smallest volume of the initial electrolyte solution, which causes coagulation of a given volume of sol, l; V sol  is the volume of the sol, l. Record the results of calculations in the table. Indicate coagulating ions. Is the Schulze-Gardi rule observed? № tube Volumeof… Results of observations Results of calculations sol water electrolyte electrolytes С ct (ммоль/л) coagulability (л/ммоль) KCl K 4 [Fe (CN) 6 ] 1 0,5 4,5 0,5 2 1 4 1 3 2 3 2 4 4 1 4 Experiment 6. Investigation of the phenomenon of protection of sols . Add 0.0025 M solution of Na 2 SO 4  from the burette to 10 ml of iron hydroxide sol until the turbidity in the solution appears. Add 1 ml of a 0.5% gelatin solution to 10 ml of Fe (OH) 3  sol solutionin another flask. Stir and add as much Na 2 SO 4  solution as required for coagulation in the first flask. What happens in the flask? Add as much electrolyte as is added already. Did coagulation occur? Explain the protective effect of gelatin. LESSON 14. FINAL CONTROL № 2 Final control № 2 contain the following topics: 1. Complex compounds 2. Chemistry of biogenic elements 3. Electrode and redox potentials. 4. Superficial phenomena. Adsorption. 5. Colloidal solutions and their properties. Theory of coagulation.