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