Espiritu, Ma. Sharmaine D. & Sy, Diane Nicole L. Superman & Wonderwoman
Espiritu, Ma. Sharmaine D. & Diane Nicole L. SL. Ma. Sharmaine D. Espiritu Sy, Diane Nicole y
The products of a chemical reaction are not necessarily in its purest form. Crystallization used in order to extract pure compound.
Addition of water to sample and boiling until it dissolves Cooling of the solution, addition of activated carbon, boiling Filtration using a syringe Cooling Paper filtration, drying Weighing
Varying solubilities Increase and decrease in solubility Saturation Crystal formation Adhesion
Weight of impure sample: 0.1 g Weight of pure crystals: 0.05 g Percent Recovery: 50% Sources of error: incomplete dissolution, excessive activated carbon, slow filtration, remaining liquid in syringe, rapid cooling, wet filter paper
1. Properties of an ideal solvent for purification by crystallization Concept of like dissolves like and polarity of substances Solubility of compound vs. impuri:es Boiling point of the solvent should also be lower than the mel:ng point of the compound
2. Should cooling be slow or rapid? Explain.
3. Advantage of water as solvent
Nonammable Nontoxic Universal solvent
4. The solubility of benzoic acid in water is 0.21 g per 100 mL of water at 10C, 0.27 g per 100 mL at 18C, 2.75 g per 100 mL at 80C and 6.80 g per 100 mL at 95C. Two students crystallized 10 g samples of benzoic acid from water, the first dissolving benzoic acid at 80C and filtering at 10C, the second dissolving the acid at 95C and filtering at 18C. Calculate the quantity of water each student was required to use and the maximum recovery of benzoic acid possible in each case.
A: At 80C At 10C
Amount of water = 100x10/2.75 = 363.64 mL
Max. Recovery = 10 (363.64x0.21/100) = 9.24 g
B: At 95C At 18C
Amount of water = 100x10/6.80 = 147.06 mL
Max. Recovery = 10 (147.06x0.27/100) = 9.60 g
4. A solid (X) is soluble in water to the extent of 1 g per 100 g of water at room temperature and 10 g per 100 g of water at the boiling point. How would you purify X from a mixture of 10 g of X with 0.1 g of impurity Y, which is completely insoluble in water, and 1 g of impurity Z, having the same solubility characteristics in water as X?
Dissolve in water and boil. Cool to room temperature, then lter (Residue: Y) Add water, heat un:l all crystals dissolve. Slowly cool and then lter. (Residue: X)
How much pure X could be obtained after one recrystallization from water?10 G1 G(HIIJKLMNHOP QHRSP KT U)/10 GL 100%=90%
90 % pure X
How much pure X could be obtained after one recrystallization from a mixture of 10 g of X with 9 g of Z?At boiling point At room temperature X recovered = 1 g
Based on the result obtained, what is suggested about the use of crystallization as a purification technique?
Inaccurate Repeated crystalliza:ons Change in solvent used
Bansal, R. (2003).A textbook of organic chemistry. (4th ed., pp. 116-117). New Delhi, India: New Age Internation (P) Limited. Welton, T. & Reichardt. C. (2011). Solvents and solvent effects in organic chemistry (4th ed.). Weinheim, Germany: Wiley-VCH Verlag & Co. Gilman, J. (1963). The art and science of growing crystals. Weinheim, Germany: John Wiley & Sons Inc. Williamson, K. & Masters, K. (2011). Macroscale and microscale organic experiments (6th ed.). Belmont, CA: Brooks/Cole.