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30 Homework exercises. 1. Write a formula for the micelle of the barium sulfate sol obtained by reacting a solution of barium chloride with a small excess of sodium sulfate solution? 2. The sol was obtained by the interaction of silver nitrate with an excess of sodium chloride. Which electrode will the sol particles moveto? 4. Write formulas for micelles of colloidal solutions for the following substances: a) silicic acid: m H 2 SiO 3  aggregate; ionic stabilizer K 2 SiO 3 → 2K + + SiO 3 2– ; b) gold hydrosol: aggregate m Au; ionic stabilizer NaAuO 2 → Na + + AuO 2 – ; c) tin dioxide: aggregate mSnO 2 ; ion stabilizer K 2 SnO 3 → 2K + + SnO 3 2– . 5. It is known, coagulation of a negative sol of silver chloride is caused by cations. For the coagulation, electrolytes such as KNO 3 , MgCl 2  and AlCl 3 were used. How are their coagulation thresholds correlated? 6. In three flasks, 100 ml of iron hydroxide (III) solution is poured. 10.5 ml of 1M KCl solution was added in the first flask to cause coagulation, in the second – 62.5 ml of 0.01 M Na 2 SO 4  solution, in the third – 37 ml of 0.001 M Na 3 PO 4  solution. Calculate the coagulation thresholds of the electrolyte and determine the sign of the charge of the particles of sol. 7. The coagulation thresholds for the following electrolytes are known (mmol/l): C ct (KNO 3 ) = 50; C ct (Na 3 PO 4 ) = 43; C ct (AlCl 3 ) = 0.079; C ct (MgSO 4 ) = 0.81. What is the charge of the sol particles? 8. The coagulation threshold of some electrolyte for the Al (OH) 3  sol is 0.63 mmol/l. What volume of 0,01 M electrolyte solution should be added to 100 ml of sol to cause its obvious coagulation? 9. The arsenic sulphide sol is formed by the addition of AsCl 3 (C eq = 0.001 mol/l) to 0.02 l H 2 S (C eq = 0.003 mol/l). a) write the equation of the reaction. b) what volume of AsCl 3  solution is needed to get positive particles? c) write the formula of the micelle sol, name the constituent parts. Questions for self-study. The phenomenon of habituation of sols. Mutual coagulation of sols. Alternation of coagulation zones. Coagulation with mixtures of electrolytes. Peptization. Colloidal protection.