Term
| what types of organic reactions require heating? |
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Definition
| Those that are very slow at room temperature |
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Term
| What types of organic reactions require cooling? |
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Definition
| Those that are exothermic at room temperature |
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Term
| In what manner do liquids boil when headed in glassware? |
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Definition
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Term
| How many boiling stones should be used to effect smooth boiling |
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Definition
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Term
| why is the addition of boiling stones to a hot liquid ill-advised? |
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Definition
| The hot liquid may suddenly boil, likely erupting from the flask |
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Term
| What manner of stirring makes the use of boiling stones unnecessary? |
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Definition
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Term
| Why should one pour a flammable liquid only after all hot heating devices have been removed from the work area? |
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Definition
| If a flammable liquid were to come into contact with a hot heating device the liquid and its flash point exceeded the liquid could ignite |
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Term
| Why is it unwise to heat a flammable liquid in an op container on a hot plate? |
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Definition
| The hot plates thermostat may provide an ignition source. |
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Term
| What type of device is used to heat round bottomed flasks? |
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Definition
| An electric heating mantle |
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Term
| Why must a heating mantle be used in conjunction with a variable transformer? |
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Definition
| Because electric heating mantles do not have controls for regulation the rate of heating |
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Term
| How is an electric heating mantle supported underneath a round bottomed flask? |
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Definition
| The electric heating mantle is supported on an iron ring or lab jack |
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Term
| With what types of laboratory equipment are hot plates used? |
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Definition
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Term
| What are the features of a typical aluminum heating block? |
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Definition
| A)Reaction tubes B)Reaction vials C)round bottomed flasks D) a thermometer |
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Term
| Under what circumstances are cooling baths used? |
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Definition
| A)Regulate an exothermic reaction B)Cool a reaction mixture prior to proceeding to a subsequent part of the procedure C) promote complete crystallization |
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Term
| What are common cooling systems? |
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Definition
| A) Cold tap water B)Ice-water mixture |
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Term
| Does the use of crushed ice alone provide efficient cooling ? |
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Definition
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Term
| Why do most organic reactions require a period of heating? |
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Definition
| They are too slow at room temperatures |
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Term
| Why is it inadvisable to heat a reaction mixture in an open container? |
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Definition
| There is the potential for loss of volatile components by evaporation |
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Term
| Why is it inadvisable to heat a reaction mixture in a closed container? |
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Definition
| Pressure will build within the closed container likely leading to an explosion |
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Term
| What is meant by the term refluxing? |
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Definition
| This term referes to the process of boiling a solution in such a way that the volatile components are condensed thereby allowing them to return to the reaction flask |
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Term
| What types of condensers are commonly used as part of a reflux apparatus? |
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Definition
| A) Water jacketed condesners (when boiling soulution is <150 degrees C) B) Air jacketed condesers (Used when the temperature of the boiling solution is >150 degrees C) |
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Term
| What is likely consequence of refluxing to vigorously? |
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Definition
| The capacity of the condeser will be exceeded resulting in the loss of volatile reagents and or products |
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Term
| How are liquids added to the flask of the reflux apparatus? How are solids added to the flask? |
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Definition
| Conical funnels are used to add liquids; powder funnels are used to add solids. |
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Term
| What steps constitute a typical solid-liquid extraction? |
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Definition
1) Addition of the solid mixture to suitable flask
2) Addition of the extraction solvent
3) Outfitting the flask for the heating under reflux 4) Refluxing of the suspension 5) Cooling of the supsension 6) Isolation of the filtrate by gravity filtration 7) Removal of the solvent by evaporation |
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Term
| What characterizes an effective solid liquid extraction solvent? |
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Definition
1) The desired component should be highly soluble in the solvent while the other components of the sample should by soluble in the solvent
2) The solvent should not react chemically in a undesirable manner with the components of the mixture
3) After the extraction the solvent should be readily separable from the solute. |
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Term
| What are the four principle categories of weak intermolecular interactions? What are their relative strengths? |
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Definition
A) Hydrogen bonding (Strongest)
B) Dipole-dipole interactions
C) Dipole-induced dipole interactions
D) Induce dipole-induced diple interactions (weakest) |
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Term
| what characterizes the reorganization of molecules as a crystalline sample melts? |
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Definition
| The molecules reorganize from fixed, orderly arrays in solids to random motions in liquids |
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Term
| What aspects about a compound can be established from its melting point? |
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Definition
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Term
| How is melting behavior affected by the presence of impurities? |
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Definition
| Impurites lead to a lowering of the melting point and a broadening of the temperature range over which the sample melts |
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Term
| In what manner is the sample placed in the Mel-Temp device? |
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Definition
| Samples are placed in small glass capillary tubes which are then place in the Mel-Temp device |
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Term
| How much sample should be added to the glass capillary tube? |
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Definition
| Approximatelly 1-2 mm of sample |
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Term
| How is melting behavior affected by the use of too much sample? |
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Definition
| The use of too much sample leads to an increase of the melting point and a broadening of the temperature range over which the sample melts |
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Term
| HOw is the rate of heating controlled when using a Mel-Temp device? |
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Definition
| Rate of heating is controlled by a variable transformer |
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Term
| What rate of heating must be used at the expected melting temperature? |
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Definition
| Approximately 1-2 degrees celcius per minute |
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Term
| Why must one prepare a fresh sample for each melting point determination? |
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Definition
| Because many organic compounds decompose on melting |
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Term
| How might melting point determination be used to identify an organic compound? |
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Definition
| Combine samples of unknown chemical with different known samples, if the range is greater than 2 degrees then it is not that chemical. |
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