Collin Jeremiah R. Balayan Answers to Questions for Experiment No.3
2013 - 14713
1. What is the purpose of washing the organic layer with 6 M NaOH? 6 M NaOH is added to the organic layer to remove the dichloromethane which is can hydrolyze to an acid. The addition of NaOH creates a new aqueous layer which is then discarded because it contains the washed out dichloromethane. 2. Compare the solid products obtained after extraction and after purification. Account for the difference between the two solids. The solid obtained after extraction was a dark powder while the solid obtained after purification were white crystals. The solid obtained from extraction is not yet pure caffeine so it has many other components that may be the reason of its dark color. The solid obtained after purification is mostly caffeine because the impurities from the solid after extraction is purified which is why it looks like white crystals. 3. What are the other applications app lications of solvent extraction? Other applications of solvent extraction include DNA purification in which the nucleases that destroy DNA are washed out, isolation of certain odors or flavors in food, purification of amines and extraction of certain metals. 4. What are the different phase changes chang es that occur during purification using sublimation? Firstly, caffeine can sublime from solid state to gas state and then quickly change from gas state to solid state. The solid state of pure caffeine can b e extracted from the sides of the th e beaker. 5. Give two advantages of sublimation over recrystallization as a purification technique. Recrystallization only gives some of the pure solid because it relies on partial precipitation precipitation of the solid while sublimation returns higher percentage yield. Sublimation is also easier to do than recrystallization because it has fewer steps. 6. Give at least two limitations of sublimation as a purification technique. In sublimation, the substance you are sublimating needs to be volatile to work. If it isn't volatile, it will not sublimate. It also needs to be the only substance in the mixture that can sublimate otherwise other substances may also join the substance you are sublimating. References: http://chem-courses.ucsd.edu/CoursePages/Uglabs/143A_Weizman/expt_3N.pdf
Collin Jeremiah R. Balayan Answers to Questions for Experiment No.4
2013 - 14713
1. Why is the chromatogram developed in an essentially closed system? The chromatogram should be in a closed system so that the container may be saturated with the vapor of the solvent and that no other gaseous substances may enter the chromatogram. 2. What are the considerations in choosing a chromatographic solvent? The solvent and the solute should have different polarities and chemical properties and can separate compounds with different R f. 3. Compare and contrast between normal phase and reverse phase chromatography. In the normal phase, a non-polar solvent is used. Hydrophilic molecules come together to form the mobile phase. While the polarity of the mobile phase is increased, the adsorption of the mobile phase decreases then the sample molecule will exit the column. In the reverse phase, a polar solvent is used. Hydrophobic molecules come together to form the mobile phase. While polarity is decreased by addition of more solvent reduces interaction between hydrophobic molecules thus making it exit the column. 4. Explain how iodine crystals help to visualize other pigments. Iodine binds to some organic compounds that are pigments and give it more color so that the pigments are easier to see. 5. Suggest one method that can be used to visualize highly conjugated compounds but are not colored. 6. Given a mixture that contains the ff. compounds: 2-chloropentane, pentanoic acid, cyclopentane and pentanal. Arrange the ff. compounds in increasing R f if the mixture is ran using paper chromatography with the same solvent system used in the experiment. Pentanoic acid -> pentanal -> 2-chloropentane -> cyclopentane References : http://chemed.clemson.edu/SCL/chromatography.html http://www.chemguide.co.uk/analysis/chromatography/paper.html http://genchem.rutgers.edu/chrompap.html
