Organic Chem 1 Lab Midterm

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What is a Material Safety Data Sheet (MSDS) and what data does it usually contain?
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Technical bulletin listing physical and chemical properties, hazards, etc of a lab reagent
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Define rules about eating, drinking, and applying cosmetics in lab.
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no eating, drinking, or applying cosmetics in lab.
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What does bumping mean and how to avoid it?
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Sudden release of vapor; use boiling chips
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National Fire Protection Association’s Diamond
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0 (low) and 4 (high) blue – health red – fire white – specific hazards yellow – reactivity
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What to do if spill on skin
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immediately wash off skin with plenty of water, and let TA know.
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If spill on person what do you do?
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Use sink or safety shower as necessary. Remove clothing (all). Do not remove safety goggles b/f washing reagent from face (this will lessen the likelihood of getting reagent in eyes).
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Define the term: melting point
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Temperature at which solid compound is in equilibrium with its liquid
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Define the term: melting point range
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Temperature range between start of liquid formation till all the solid becomes liquid
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Define the term: impurity
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Any admixture in the compound of interest
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Define: eutectic composition
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when both solids are in equilibrium with the liquid
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Define: eutectic temperature
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the lowest possible melting point for a mixture of X and Y
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Describe the purpose and technique of taking mixture m.p.
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To proof identity of unknown compound: mix known and unknown compounds. If mixture mp is the same as mp of known compound, unknown and known compound are the same
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Explain the phenomena (name the process): compound to melt is darkening when heating and release gas when melting
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Decomposition
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Explain the phenomena (name the process): compound disappears from capillary when attempting to measure its m.p.
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Sublimation
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Define: orientation mp
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if mp is unknown then first measure the approximate melting point of the compound. Then you let appratus cool to 15 degrees below the orientation mp; new sample is heated increasing the temp at 1-2 degrees Celsius per minute to get the accurate mp.
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Errors in observed mp
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1) placement of too much sample into the capillary tube (poor heat transfer) – should be 2-3 mg 2) not grinding particles (poor heat transfer)
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define: sweating
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droplets on outside surface of sample, due to insufficient drying
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define: decompose
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darkening in the color of the compound as it melts
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define: sublimation
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passes directly from solid to vapor, the compound disappears – sample vaporizes and recrystallizes higher up in capillary tube
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In distillation Term volatile is related to a chemical having (true or false): 1) Low pressure at high temperature 2) High pressure at high temperature 3) High pressure at low temperature
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1) F 2) F 3) T
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Define: distillation
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technique used for separating compounds based on differences in their bp
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Distillation was made using 15 mL of each cyclohexane and toluene. With what scale:
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Macro
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define: pot
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where volatile compounds are heated to boiling in one container
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define: condenser (explain how used)
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where the vapors that are produced are then cooled and re-liquefied by passing them through a water cooled condenser
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define: receiver
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where the re-liquified cooled produces are collected
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define: evaporation
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transition from liquid to vapor on only those molecules at the liquid surface (happens at temp below the bp of compound)
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define equilibrium vapor pressure:
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pressure exerted by these gaseous molecules on the walls of the container
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Define: boiling point
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Temperature, at which vapor pressure of liquid equals external pressure
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define: miscible
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liquids mix
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Distillation of miscible liquids best described using:
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Rault’s Law
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Write the equation for Rault’s law and define the terms
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PT = P1X1 + P2X2 PT – total pressure P1,2 – partial pressure X1,2 – molar fraction of component
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Define: distillate
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when the vapors condense into a liquid, and have the same composition as the vapors formed
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Define: simple distillation
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if one compound is much more volatile than the other
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What makes fractional distillation different from simple distillation?
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it has a fractionating column between the pot and distilling head
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True or False: Vapors over the mixture of cyclohexane and toluene contain the higher percentage of cyclohexane than that in mixture
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True
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B.p. of mixture of 2 liquids is always (T or F) 1) Lower than b.p. of both components 2) Higher than b.p. of both components 3) In between the b.ps. of both components
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1) false 2) false 3) true
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True or False: Fractional distillation is preferable if difference in b.p. of mixture components is lower than 40 degrees C
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True
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State two rules not to break when performing distillation
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Do not distil to dryness Do not heat closed system
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Define: recrystallization
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purification process used to remove impurities from organic compounds that are solid at room temp
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Define: oiling out
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when a compound is insoluble in a solution at a temp above the compound’s mp. As a result the compound is deposited as an oil, and not crystals
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How to choose a good solvent
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room temp: insoluble bp: soluble ice: insoulble
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Define: solvent pair
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two solvents are used to dissolve compound
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define: filter flask
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flask with a sidearm
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equation for percent recovery
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(mass of recrystallized compound in g / mass of crude compound in g) (100%)
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How to tell is compound is pure
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it melts at a range of 1-3 degrees Celsius near its reported melting point
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If crystals don’t form what can you do?
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1) scratch glass to give crystals sites to form 2) put seed crystal of pure compound into the soln
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If solution has colored impurities
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add activated carbon
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How to avoid premature crystallization in the funnel stem
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heat funnel, filter paper, and collection flask
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Define: eluent
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a solvent used as a mobile phase
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TLC
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thin layer chromatography
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Equation for Rf
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distance traveled by comp, mm / distance traveled by solvent, mm
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define: eluent front
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the point that the eluent has reached
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the more polar the eluent
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the greater its eluting power, ability to move compounds over the absorbent surface
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Name 3 main parts of Gas Chromatograph
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Injector, column, detector
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Chromatogram after analysis of some mixture shows several peaks. Ratio of components in the mixture is proportional to:
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Area peaks
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What solvent was suitable for separation of 2 polar compounds using silica gel:
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toluene or ethyl ether
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State 2 methods of visualizing TLC plates
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Under UV-light or in iodine chamber
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Write the equation for the % recovery in column chromatography
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(mass of recovered compound / mass of compound in original mixture) (100%)
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Calculate the mass of components in 170 mg of 1:1:3 mixture (by mass) of ferrocene, acetylferrocene and alumina
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1+1+3 = 5 parts total; 170mg/5parts = 34mg [1 part] of each ferrocene and acetylferrocene; 34×3[parts]=102mg of alumina
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Describe the consequences of column dry-out during a separation
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Air bubbles will form in sorbent bed. Those bubbles may prevent solvent from moving through bed, and mixture to separate
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Define: Extraction
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process that selectively dissolves one or more of the mixture compounds into an appropriate solvent
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define: washing
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reverse process of extraction, in which the impurities are removed to the second solvent, leaving the desired compound in the original solvent
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define: emulsion
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suspension of small droplets of one liquid into another liquid
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Codistillation (including steam distillation) is possible if components of mixture are:
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Immiscible
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State why Steam distillation is preferable for compound that boils at high temperature (>250 C at 1atm)
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Distillation of compound at lower temperature lower risk of thermal decomposition
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Clove oil components are:
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eugenol eugenole acetate
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Will eugenol or eugenol acetate react with sodium hydroxide? What functional group will the reaction occur at?
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eugenol on the -OH group
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When two liquids are immiscible the equation used is?
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Dalton’s Law
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Match the compounds and reagents used to separate mixture by extraction: acetanilide NaOH t-butylphenol none p-Toluic acid NaHCO3
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acetanilide – none t-butylphenol – NaOH p-Toluic acid – NaHCO3
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Describe how properly release pressure buildup in separatory flask during the extraction
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Turn separatory funnel upside down and carefully open stopcock
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Calculate % recovery of each component if 1.0 g each acetanilide, t-butylphenol and p-toluic acid isolated from 4.3 g of 1:1:1 mixture (molar ratio) acetanilide MW = 135 g/mol t-butylphenol MW = 150 g/mol p-toluic acid MW = 136 g/mol
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If 1 mole of each component, mass of mixture will be 135+150+136=421g 4.3g of mixture will correspond to 4.3/421=0.0102mole of each component Starting amounts: Acetanilide, g = 0.0102mole x 135g/mole = 1.37g; t-Butylphenol, g = 0.0102mole x 150g/mole = 1.53g; p-Toluic acid, g = 0.0102mole x 136g/mole = 1.36g %recovery acetanilide = (1.0g/1.37g)x100% = 73% %recovery t-butylphenol = (1.0g/1.53g)x100% = 65% %recovery p-tolic acid = (1.0g/1.36g)x100% = 74%
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Sterochemistry
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right is R Left is S
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Assuming solvolysis of 2-chloro-2-methylpropane proceeds as SN1 reaction, does rate of reaction depends on NaOH concentration?
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No

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