What to Expect on the CHEM 232 final exam, scheduled for 7:30-8:20 p.m. Monday, December 15, 2014
The exam consists of 10 multiple choice problems covering experiments # 6-11 and IR spectroscopy. The exam is worth 50 points and each problems is 5 point. You will have 45 minutes to complete the exam.
The exam will cover the following areas:
• Process of distillation and how fractional distillation improves component separation over simple distillation
• Questions related to how the composition of a sample of distillation products is analyzed by GC, as well as the mathematics involved in GC analysis. • Questions about other aspects of calculations (or the logic behind calculations performed) required to do analysis of experimental data, including calculating numbers of moles which react from density or molar concentration of stock and determination of limiting reagent.
• Questions about the mechanism of reaction of the SN2, beta-elimination (E2) and free radical chlorination reactions. That means:
• Being able to mechanisms of all three reactions
• What makes a good leaving group or good nucleophile;
• What role degree of substitution at the carbon where attack occurs plays in determining the mechanism of each reaction;
• When and how the stability of an intermediate transition state dictates the relative composition of the products in the mixture
• Knowing how to identify the products formed either by GC analysis or chemical test.
• A question requiring analysis of an IR spectrum from a table of frequencies associated with specific functional groups (to be given you; no memorization required), leading to identification of the molecule which gave the spectrum. The following reviews details of the course content that may prove to be useful in studying for the exam.
• Essential principle: understanding boiling point
• liquid molecules are in constant motion
• those at surface can escape into the vapor phase; and will continue to do so until a dynamic equilibrium between liquid molecules escaping and vapor molecules reentering the liquid phase is established
• When temperature rises, molecular motion, #molecules escaping and equilibrium
vapor pressure all increase.
• The total pressure is the sum of the vapor pressure of the liquid and that of air • When a temperature is reached at which equilibrium vapor pressure of the sample equals the total pressure, rate of evaporation increases dramatically, bubbles form and the sample boils.
• Allows separation of components if their boiling points differ by 40-50°C °
• How does this play out theoretically?
• A liquid mixture will have a specific boiling point based on the mole fraction of each component in the mixture
• The composition of the vapor at that temperature will be richer in the more volatile species than the original mixture.
• If some of that vapor condenses, the composition of the condensed liquid will now be that of the vapor, which will have a boiling temperature lower than that of the initial vapor.
• The vapor generated from this new liquid mixture during a second “distillation” will now be even richer in the more volatile species.
• If the lower portion of a distillation column is at a higher temperature than the top, some condensed vapor will revaporize, even as it flows down the column to return to the still-pot
• Ideal temperature differential should be: at the bottom of the column: ~bp of the less volatile component; at the top: ~bp of the more volatile component • Uncondensed vapor and revaporized samples rise ever higher in the column and undergo repeated condensations and revaporizations, becoming richer in the more volatile component with each.
• This is the equivalent of doing multiple simple distillations within a column. It is measured as HETP (height equivalent of a theoretical plate), the vertical length of the column necessary to obtain separation of one...
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