TECHNOLOGICAL INSTITUTE OF THE PHILIPPINES COMPETENCY EXAM CRYSTALLIZATION STUDENT NO.:_______________ DATE:______________________ Answers: A B C D A B C D 1 11 2 12 3 13 4 14 5 15 6 16 7 17 8 18 9 19 10 20 Linked Problems 1-2 A hot solution of Ba(NO 3)2 from an evaporator contains 30.6 kg Ba(NO3)2 per 100 kg water and goes to a crystallizer, where the solution is cooled and Ba(NO3)2 crystallizes. On cooling, 10% of the original water evaporates. For a feed solution of 100 kg total, calculate the following: 1. The yield of crystals if the solution is cooled to 290K, where the solubility is 8.6 kg Ba(NO3)2 per 100 kg water a) 10.2 kg Ba(NO3)2 c) 17.5 kg Ba(NO3)2 b) 9.36 kg Ba(NO3)2 d) NOTG 2. The yield of crystals if the solution is cooled, where the solubility is 7.0 kg Ba(NO 3)2 per 100 kg water a) 10.2 kg Ba(NO3)2 c) 8.36 kg Ba(NO3)2 b) 18.61 kg Ba(NO3)2 d) NOTG Linked Problems 3-4 A batch of 1000 kg of KCl dissolved in sufficient water to make a saturated solution of 363K, where the solubility is 35 wt% KCl in water. The solution is cooled to 293K, at which temperature its solubility is 25.4 wt%. 3. The weight of crystals obtained is a) 287.62 kg c) 168.62 kg b) 367.68 kg d) NOTG 4. What is the weight of crystals obtained if 5% of the original water evaporates on cooling? a) 187.56 kg c) 168.56 kg b) 399.29 kg d) NOTG Linked Problems 5-6 Given: The solubility of benzoic acid in water is 0.29 g of benzoic acid per 100 ml of water at 20 ºC, and 4.6 g benzoic acid per 100 ml of water at 90 ºC.
5. What mass of benzoic acid should be recovered when 200 mL of water is used to recrystallize a 5 g sample of the acid a) 1.2 g c) 3.42 g b) 2.34 g d) 4.42 g 6. What would be the maximum theoretical percent recovery from crystallization of 5.00 g of solid “X” from 100 ml water? a) 24% c) 68.40% b) 46.8% d) 88.40% Linked Problems 7-8 A saturated solution containing 1500kg of potassium chloride at 360K is cooled in an open tank to 290K. if the density of the solution is 1200 kg/m3, the solubility of potassium chloride per 100 parts of water by mass is 53.55 at 360K and 34.5 at 290K calculate: 5. The capacity of the tank required is a) 1.36 m3 c) 6.56 m3 3 b) 3.58 m d) NOTG 6. The mass of crystals obtained, neglecting any loss of water by evaporation is a) 56 kg c) 65 kg b) 534 kg d) NOTG Linked Problems 9-10 A solution of RbCl contains 28 g of rubidium chloride. This solution is to be concentrated by evaporation of water to get a saturated solution at 100°C and then cooled to 20°C. The solubility of RbCl is 91,1 g per 100 g of water at 20°C and 138,9 g per 1 00 g of water at 100°C. 9. Calculate the mass of the saturated solution after evaporation of the excess of water. a) 50.2 g c) 48.2 g b) 64.2 g d) 32.4 g 10. Calculate the mass of the separated crystals. a) 9.6 g c) 12.2 g b) 10.3 g d) 5.6 g A feed solution of 10000 lbm at 130F containing 47 lb FeSO4 per 100 lb total water is cooled at 80°F, where FeSO4•7H2O crystals are removed. The solubility of the salt at 80F is 30.5 lb FeSO4 per 100 lb water. The average heat capacity of the feed solution is 0.70 BTU/lbm-F. The heat of solution is -4.4 kcal/gmol FeSO4•7H2O. Assume that no water is vaporized. 7. Calculate the yield of crystals a) 1715 lbm c) 2804 lbm b) 7196 lbm d) NOTG 8. Make a heat balance, The QT is a) 135.235 BTU c) 50.356 BTU b) -430.049 BTU d) NOTG 9. A solution of NH4Cl is saturated at 70°C. Calculate the temperature to which this solution must be cooled in order to crystallize out of 45% of the NH4Cl. The solubility of NH4Cl in water are: Temperature, °C 70 10 0 Solubility, g/100g water 60.2 33.3 29.4 a) 9.51°C c) 20.15°C b) 35.25°C d) NOTG
10. The feed to a cooling crystallizer is 1000 lb/hr at 120°F. The solution is cooled to 70°F. It has a 3 ft2 of cooling surface per foot of running length of crystallizer. The required rate of heat transfer is 44,900 BTU/hr. cooling will be provided by a countercurrent flow of chilled water entering the cooling jacket at 60°F, leaving at 85°F. The overall heat transfer coefficient, U, is expected to be 20 BTU/hr-ft2-°F. the length of the crystallizer is a) 37.5 ft c) 28.5 ft b) 10.6 ft d) NOTG 11. The solubility of sodium bicarbonate in water is 9.6g/100g of water at 20°C and 16.4g/100g of water at 60°C. If a saturated solution of NaHCO3 at 60°C is cooled to 20°C, what percentage of the dissolved salt crystallizes out? a) 68.5% c) 86.3% b) 41.5% d) NOTG 12. If sodium chloride solution, at a temperature of 40°C, has a concentration of 50% when the solubility of sodium chloride at this temperature is 36.6 g / 100 g water, calculate the quantity of sodium chloride crystals that will form once crystallization has been started. a) 36.5 kg c) 63.4 g b) 23.6 kg d) NOTG 13. A tank holds 10,000 kg of a saturated Na 2CO3 at 30°C. you want to crystallize from this solution 3000 kg of Na2CO3•10H2O without accompanying water. To what temperature must the solution be cooled? Temperature, °C 10 20 30 Solubility, g/100g water 12.5 21.5 38.8 a) 25.9 °C c) 20.2 °C b) 15.3 °C d) NOTG 14. 1000 kg of FeCl3•6H2O are added to a mixture crystals of FeCl3•H2O to produce a mixture of FeCl3•2.5H2O crystals. How much FeCl3•H2O must be added to produce the most FeCl3•2.5H2O? a) 2556.1 kg c) 1556.1 kg b) 1056.1 kg d) NOTG 15. 8000 kg of an aqueous solution containing 25 percent (by weight) of anhydrous sodium sulfate are fed to a crystallizer. The solution is cooled and 15% of the initial water is lost by evaporation. Na2SO4.10H2O crystallizes out. If the mother liquor (solution after crystallization) contains 18.3% (by weight) of anhydrous Na2SO4, calculate the weight of crystals obtained. a) 2716 kg c) 4384 kg b) 6584 kg d) NOTG 16. The heat required when 1 kmol of MgSO4•7H2O is dissolved isothermally at 291 K in a large mass of water is 13.3 MJ. What is the heat of crystallization per unit mass of the salt?
a) 53.9 kJ/kg b) 12.3 kJ/kg
b) 65.3 kJ/kg d) NOTG
17. A batch of 1500 kg of saturated potassium chloride solution is cooled from 360 K to 290 K in an unagitated tank. If the solubilities of KCl are 53 and 34 kg/100 kg water at 360 K and 290 K respectively and water losses due to evaporation may be neglected, what is the yield of crystals? a) 365 kg c) 186 kg b) 236 kg d) NOTG 18. If sodium chloride solution, at a temperature of 40°C, has a concentration of 50% when the solubility of sodium chloride at this temperature is 36.6 g / 100 g water, calculate the quantity of sodium chloride crystals that will form once crystallization has been started. a) 36.5 kg c) 63.4 g b) 23.6 kg d) NOTG 19. Rasorite containing 85% Na2B4O7•4H2O is dissolved, filtered, and run to the crystallizer as a 25% solution of borax, Na2B4O7•10H2O at 150°F. After cooling to 100°F. The crystals are centrifuged and go to the drier containing 5% moisture. The mother liquor contains 8% borax. What yield of the crystals is obtained per ton of rasorite processed? a) 3.81 tons c) 4.2 tons b) 0.93 tons d) NOTG 20. A tank holds 10,000 kg of a saturated Na 2CO3 at 30°C. you want to crystallize from this solution 3000 kg of Na2CO3•10H2O without accompanying water. To what temperature must the solution be cooled? Temperature, °C 10 20 30 Solubility, g/100g water 12.5 21.5 38.8 a) 25.9 °C c) 20.2 °C b) 15.3 °C d) NOTG
