Recrystallization of Benzoic Acid Outline
Experiment 1: Purification of Benzoic Acid by Recrystallization
III. Introduction
Purification - physical separation of impurities and by-products from an impure sample pure substance. *Distillation- for liquid compounds,
*Recrystallization- solid compounds
Recrystallization
- precipitation of a solid cpd. from a saturated solution in the form of crystals through cooling or evaporation
-7 steps: 1) selecting the appropriate solvent 2) dissolving the solute 3) decolorizing the solution 4) removing suspended solids 5) crystallizing the solute 6) collecting and washing the crystals 7) drying the product
- 2 Kinds of Impurities: 1) more soluble
2) less soluble than the main component
- impure solid first dissolved in an appropriate solvent when heated
- appropriate/ideal solvent = dissolves component to be purified when hot (boiling point), = does NOT dissolve component to be purified when cold= room temp. or 0oC = either dissolves impurities when cold OR does NOT dissolve impurities when hot
- components will then crystallize in its purer form as the solution is cooled. Less soluble component will crystallize first As the crystals are formed, the correct molecules that will fit in the crystal lattice are selected while the wrong molecules are ignored, resulting in a pure solid
- Depends on: 1) solubility of the compound 2) differences in solubility of the desired solutes & impurities dissolved in the solvent
- Common Solvents Used: Solvent | Formula | Polarity | Boiling Pt. (oC) | Water | H2O | Very Polar | 100 | Ethanol | CH3CH2OH | Polar | 78 | Methanol | CH3OH | Polar | 65 | dichloromethane | CH2Cl2 | Slightly Polar | 40 | Diethyl ether | (CH3CH2)2O | Slightly Polar | 35 |
IV. Experimental 0.100 g of powdered impure benzoic acid, 1 small piece of boiling chip, and 2 mL of distilled water were added respectively into a vial. While swirling
III. Introduction
Purification - physical separation of impurities and by-products from an impure sample pure substance. *Distillation- for liquid compounds,
*Recrystallization- solid compounds
Recrystallization
- precipitation of a solid cpd. from a saturated solution in the form of crystals through cooling or evaporation
-7 steps: 1) selecting the appropriate solvent 2) dissolving the solute 3) decolorizing the solution 4) removing suspended solids 5) crystallizing the solute 6) collecting and washing the crystals 7) drying the product
- 2 Kinds of Impurities: 1) more soluble
2) less soluble than the main component
- impure solid first dissolved in an appropriate solvent when heated
- appropriate/ideal solvent = dissolves component to be purified when hot (boiling point), = does NOT dissolve component to be purified when cold= room temp. or 0oC = either dissolves impurities when cold OR does NOT dissolve impurities when hot
- components will then crystallize in its purer form as the solution is cooled. Less soluble component will crystallize first As the crystals are formed, the correct molecules that will fit in the crystal lattice are selected while the wrong molecules are ignored, resulting in a pure solid
- Depends on: 1) solubility of the compound 2) differences in solubility of the desired solutes & impurities dissolved in the solvent
- Common Solvents Used: Solvent | Formula | Polarity | Boiling Pt. (oC) | Water | H2O | Very Polar | 100 | Ethanol | CH3CH2OH | Polar | 78 | Methanol | CH3OH | Polar | 65 | dichloromethane | CH2Cl2 | Slightly Polar | 40 | Diethyl ether | (CH3CH2)2O | Slightly Polar | 35 |
IV. Experimental 0.100 g of powdered impure benzoic acid, 1 small piece of boiling chip, and 2 mL of distilled water were added respectively into a vial. While swirling
References: “Crystallization.” University of Colorado. University of Colorado, n.d. Web. 4 Feb. 2013 <http://orgchem.colorado.edu/CCCE/frame/images/handbook.pdf>. “Recrystallization.” Hartnell College. Hartnell College, n.d. Web. 17 Dec. 2012. <http://www. hartnell.edu/faculty/shovde/chem12a/lablecturehandouts/recrystallizationlecture.htm>. “Recrystallization: a purification technique for solids.” German Jordanian University. German Jordanian University, n.d. Web. 17 Dec. 2012. <www.gju.edu.jo/admin/s32files/3-RECR.doc>.