CHEM 2100L Quiz 1
The solvent must be ______ _______ (should not react with the target compound or impurities)
chemically inert
Mixed melting point determination: choose 2 compounds with _____ or _____ MP's than your unknown, make two samples- a _/_ mixture, finding MP's for both mixed samples using the _____ ____ apparatus
comparable higher, 50/50, Mel-temp
The goal of recrystallization is to ______ and subsequently _______ a pure substance from the solution
dissolve, crystallize
If you cool the flask in an ice-bath and crystals do not form at this stage, you most likely used an ______ amount of solvent. You should _____ away a portion of the remaining solvent and attempt to induce crystallization again.
excessive, boil
Separation of impurities via hot filtration: fold ______ filter paper, _____ temperature ______ filtration
fluted, high gravity
One percent of impurity results in a ____ C melting point depression
0.5
_______ _______ is the lowest possible melting point of a mixture of two substances
Eutectic point
Experiment 1 is ________-Identification of an _______ unknown
Recrystallization, impure
Five Steps of Recrystallization: 1. Choose an _________ _________ 2. _______ the impure mixture in the ______ _______ 3. Remove the ______ _______ from the solution via ____ temperature _____ filtration 4._______ the solution to induce ______ of the pure compound 5. Isolate the _____ crystals via ______ ________
appropriate solvent, dissolve hot solvent, insoluble impurities high gravity, Cool recrystallization, pure suction filtration
Impurities ______ and ______ a pure compound MP range
broaden, depress
Impurities both ______ and ______ a pure compound's melting point range.
broaden, depress
For an impure mixture, the melting point range is typically ______ and _______ than the melting point ranges of either pure compound
broader, lower
MelTemp apparatus contains a _____ ____, ______ ______, ____ ______, and ______ ______
heating block, thermometer control, thermometer well, and capillary holder
A suitable solvent will dissolve your target compound at ______ temperature but not at _______ temperature.
high, room
Experimental procedure: 1. Heat water using ______ _____ 2. Add a ______ amount of hot water to the flask that contains your unknown compound and dissolve your unknown by heating 3. Use ____ _____ _____ to remove insoluble impurities from unknown
hot plate, small, hot gravity filtration
Exp. Procedure Cont'd: 7. Determine the ______ ______ of the unknown 8. Choose 2 compounds with which to perform mixing MP's 9. ______ data
melting point, record
Use a _______ ________ of solvent to dissolve the impure solid.
minimum amount
Pure compounds exhibit a _____ melting point range; pure benzoic acid: _____-______ C
narrow, 122-123
Mixing melting point determination: If 1 is your unknown, you will ____ see a change in MP range of the mixture of the unknown and compound 1. If 1 is your unknown, you will see a _______ ______ in the melting point range of the mixture of the unknown and compound 2
not, marked change
Recrystallization is a lab technique used for the purification of ______ ______ compounds.
organic solid
Use of excess solvent will make it difficult to ______ _______ ______
recover pure unknown
Exp. Procedure Cont'd: 4. Cool the flask to ____ temp 5. If no crystals have formed, induce crystallization by ______ inner walls of flask with a _____ ______ 6. Cool flask in an ice-bath and collect the pure unknown via _______ _______
room, scratching glass rod, suction filtration
If crystals do not form after removing the flask from the hot plate and cooling it to room temp., induce crystallization by _____ the inner walls of flask with _______ _____ or introduce a _____ _____ (of the pure compound
scratch stirring rod, seed crystal
Mel Temp apparatus and melting point determination: load a ______ amount of the ___ product crystals into a melting point _______ ____, place the ______ and ____ _____ into the appropriate wells, obtain a rough estimate of the ____ _____ using a higher heat setting initially, allow the mel-temp to cool roughly to _____ C below the preliminary MP, and select a _____ heat setting to obtain a more ______ MP.
small dry capillary tube, thermometer capillary tubes, melting point, 20, lower accurate
A melting point is when the temperature of a compounds ______ and ______ phases are in _______.
solid, liquid, equilibrium
The impurities present in the mixture must either be _______ in the solvent at room temperature or _______ at high temperature
soluble, insoluble
Isolating the pure compound via suction filtration: Use the thick walled rubber hose for ______ (black or red), always clamp your ______ ____ at the ______ of the flask, use a _____ ______ to achieve proper suction, and wet the filter paper to adhere it to the bottom of the ______ ______ prior to filtration.
vacuum, filter apparatus neck, neoprene adaptor, Buchner funnel
Solvent must be ______; relatively ___ _______ point and hence easy to remove
volatile, low boiling