Organic Chemistry Lab Midterm – Flashcards
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Molecular structure of cyclohexane
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just a simple cyclo-6 carbon. C6H12
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Molecular structure of Toluene
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a benzene with a CH3 attached on the top Carbon. C7H8
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What is the purpose of distilling something?
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separating compounds based on differences in their boiling points.
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What kind of mixture is used for simple & fractional procedure?
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volatile compounds in this case cyclohexane and toluene.
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purpose of boiling stones
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to avoid "bumping" which is the sudden eruptive release of vapor
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Define boiling point
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the temperature at which the vapor pressure of the liquid is equal to the external pressure applied to the surface of the liquid. This external pressure is commonly atmospheric pressure.
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What is a distillate?
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A liquid condensed from vapor in distillation. A purified form.
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What is volatile?
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Having relatively high vapor pressures and low boiling points.
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What is a theoretical plate and what apparatus has more of them?
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Each condensation and revaporization that occurs on a fractionating column is called a theoretical plate. A fractionating column with a large number of theoretical plates accomplishes many condensation-revaporization steps and very efficiently separates the compounds in a mixture. Fractional.
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What is a condensation line?
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a condensation line of vapor can be observed as it moves up the distilling head.
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When do you use simple distillation?
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when boiling points are far apart and nonvolatile
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When do you use fractional distillation?
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volatile fluids with close boiling points
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Movement water through condenser
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The fluid is evaporated and then liquifies as it moves though the condensor. As the condensed liquid falls toward the pot, the pot gradually contains a higher and higher percent of the less volatile compound. Thus, a separation of the two compounds is achieved.
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What is codistillation?
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Distillation performed on mixtures in which the two compounds are not miscible.
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What is steam distillation?
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When one of the compounds being distilled is water
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What does steam distillation avoid?
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This process avoids decomposition, that might occur at the normal boiling point of the compound of interest.
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What kind of mixture is used for the clove oil procedure?
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an excess of water is added to the compound of interest in a distilling flask.
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Iron III chloride Test
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Is a test for phenols. The formation of a red, blue, green, or purple coloration indicates the presence of phenols.
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Testing with potassium permanganate
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Test for alkene and alkyne. The disappearance of the purple color and the appearance of a brown suspension is a positive test.
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Testing with Bromine in Dichloromethane
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triple bonds and phenols.he formation of a white precipitate (a brominated phenol) indicates that the unknown was a phenol.
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What is an emulsions?
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a mixture of two or more liquids that are normally immiscible
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What class of organic compounds does caffeine belong to?
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alkaloids
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What is a drying agent?
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a substance that promotes drying
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Recrystallization of caffeine
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Evaporate the remaining dichloromethane from the crude caffeine • Dissolve the crude caffeine crystals in a minimal amount of hot 2-propanol, cool, and add hexane • Filter the purified caffeine and wash with 1:1 diethyl ether/hexane solution • Weigh the crystals
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Melting point of caffeine
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234-236
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molar mass of caffeine
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194.19 g/mol
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Purpose of activated charcoal
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purification
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How did you purify acetanilide?
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Recrystallization
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What is the difference between the treated and untreated product?
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treated product will be free of impurities (white) and lighter
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What does recrystallization do?
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used to remove impurities from organic compounds that are solid at room temperature.
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For recrystallization of acetanilide: Do you want your compound to be soluble or insoluble at room temperature?
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insoluble
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For recrystallization of acetanilide:Do you want your compound to be soluble or insoluble at hot temperatures?
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soluble
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What is "oiling out"?
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if a solvent's boiling point is higher than the compound's melting point
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What is a solvent pair?
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Two solvents are selected that are miscible with each other, but have opposite abilities to dissolve the compound.
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What is a solvent?
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A substance that dissolves a Solute
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Criteria for selecting recrystallizing solvent?
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(1) Compound being purified must be insoluble in solvent at room temperature (2) Compound must be soluble in boiling solvent (3) Solvent's boiling point must be lower than the compound's melting point (4) An abundant quantity of crystals must be recoverable from the cool solvent
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Vacuuming filter is (faster or slower) and gives you (more or less) product
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faster; less product
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Gravity filter is (faster or slower) and gives you (more or less) product
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slower; more product
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What is a melting point range?
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the span of temperature from the point at which the crystals first begin to liquefy to the point at which the entire sample is liquid.
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eutectic temperature
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The lowest temperature at which a mixture of two elements will completely melt.
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eutectic composition
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both solid X and solid Y are in equilib. with the liquid
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How can you tell if something is pure using melting point range?
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1-2 C melting point range reveals a pure compound
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Orientation melting point
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The melting point at which the sample is heated 10-15 C until it melts and then cooled to 15 below the "orientation melting point"
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What is sweating?
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Sometimes slight changes, such as shrinking and sagging, occur in the crystalline structure of the sample before melting occurs. Also, traces of solvent may be present due to insufficient drying and may appear as droplets on the outside surface of the sample.
