EXP 5: SIMPLE DISTILLATION AND GC

Distillation is the most practical method for ______ 3 advantages??

purifying liquids on a large scale. can be scaled up, if complex apparatus, can separate even 1 degree bp diff compounds, very cimple if large bp diff

___ heating can drive heated vapor up the column, preventing the formation of an ____ that allows the ____ boiling component to separate, thus ____ the number of theoretical plates and ____ the separation.

rapid equilibrium lower decreasing decreasing

simple distillation procedure

-Put boiling chips/stir bar in reaction vial THEN ADD MIXTURE (pentane/heptane or hexane/heptane) -Clamp rxn vial, GREASE glass joints, and connect Keck clamp (should be right above heating surface) to distillation head to air condenser UNDER HOOD . -place thermocouple -Place vial into mantle and place tiles -CORK sidearm and plug mantle into VARIAC at 40 V (alter based on distillate collection speed) -Measure temperature once liquid starts collecting. -Collect three 0.8 mL fractions in Teflon-capped vials with pipet, measuring temperature each time. -Turn off Variac, remove mantle, and LET COOL. -FINALLY: take fourth fraction of remaining liquid in a vial.

An ____was placed under the screw cap under the thermocouple adapter to _______

O-ring adjust and maintain the thermocouple at the appropriate height

It should be obvious that all fractions collected in the simple distillation will ______of both components. Even in a fractional distillation with many tp's, the ___ fractions will not be pure. The highest purity will be obtained in the_____

contain significant amounts middle initial and final fractions.

boiling chips were added to the distilling flask to _____

disperse molecules and prevent a large gas bubble from expanding and breaking the glass while heating due to pressure build-up.

The temperature in the distilling flask and the lower part of the apparatus will continue to ____ as this higher boiling component begins its way up the column. This provides the ___ necessary to ____ the condensate in the upper part of the apparatus.

rise energy vaporize

why do we cork the sidearm

prevents distillate from evaporating

Grease is essential because it___ between the two pieces of glass. Glass will expand and contract during heating; without grease, the joints may ____

provides a release layer form a tight bond (the joint freezes).

distinct downside for fractional distillation is that it is much -____, because a gradual ______is required within the fractionating column. ____ must be maintained. If the pot is heated too rapidly, the liquid holdup can get too great and swamp the column.

slower temperature gradient Equilibrium

The alkane mixtures being compared this semester are _____

pentane/heptane and hexane/heptane.

why was water not allowed to clean the glassware

the glassware was left so remaining liquids/cleaning acetone could evaporate off it (NO WATER EXPOSURE--contaminates for next use)

For frosted glass joints, you want to use just enough grease to make ___. Remember, this grease is a ___ that will flow, and some will ___ into your apparatus and your distillate.

the joint clear (translucent) viscous silicone oil contaminate if too much grease

We want to know the composition of each fraction you inject into the GC. to do this, we need to make several assumptions. The first assumption is that _____ Fortunately, for the Thermal Conductivity Detector used in our instruments, this is fairly true since our analyzed compounds are so similar in structure and composition.

the response factor for the peaks is the same (the size of signal for the amount of compound in the gas passing the detector is the same for all components).

the heating mantle was plugged into the Variac, why not wall outlet? what two checks should be done to ensure the thermocouple is working right?

the wall outlet could overheat the mantle and is non-adjustable due to its unregulated current 1-the thermocouple was connected to the thermometer and checked to ensure the temperature was indeed positive and a reasonable temperature inside the apparatus (to check that the heating mantle was plugged in the correct direction as it has a polarity). 2-After the heating mantle was actually turned on at 40 V, the back of the hand was placed near, but not too close, to the mantle to ensure it was heating up and that the fuse had not blown

in GC the _______equals the % composition of each fraction.

% area under each curve

Simple distillation what is the one difference in apparatus for fractional distillation

- Liquids that boil below 150 C and have atleast 25C difference in boiling temperature. - Consists of a distilling flask (containing combined solution), distillation column ( thermometer, condenser, and receiving flask to collect the distillate. -FRACTIONATING COLUMN packed with glass beads or helices provides more surface area for the vapor to contact, increasing theoretical plates.

Itt is safe to distill most organic compounds boiling up to about 150 °C. Two things are required if you go much higher.

-omit use of cooling water in the condenser. With cooling water, the temperature difference is so great (>120 °C) that you are running the risk of thermally fracturing the condenser. The liquid will condense without the need for water circulating in the condenser. -consider the thermal stability of your product. If it is an aromatic or an ester, you can probably distill at higher temperatures without risking much decomposition. Otherwise, you may lose product to decomposition.

cons of distllation

-volatile compounds only but many organic compounds have too high bps (solution:vacuum distillation @ low pressure) -compounds must not decompose (must be heat stable) -high product loss in microscale -some mixtures form non-separable azeotropes Separation of materials with close boiling points is not feasible on a small scale.

_____ at a given temperature will have some molecules escaping into the gas phase. (A pan of water will ____ by this process.) The_____will create a pressure called the vapor pressure.

Any liquid slowly evaporate to dryness gaseous vapor in equilibrium with a liquid

____ in both distillations could have condensed more of the vapor rather than___ , _______ % yield.

Better cooling letting it escape the column, increasing

LET APPARATUS ___ before taking apart--can cause __.

COOL fire

why do we ___ all ground glass joints

GREASE, or it might expand and become stuck/unusable in the future

are glycerol and grease interchangeable? why or why not

Glycerol is used to lubricate hoses before attaching them to glassware. Grease is for use between ground-glass joints. The two are not interchangeable.

___ bp compounds have longer retention time because they spend much of the initial time in the GC as _____ and take ____ to heat up, evaporate, and move through the GC tube than ____ bp compounds.

High liquids longer lower

___ follow Raoult's Law, with the _____ always proportional to the ____ of each component.

Ideal liquids vapor pressure mole fraction

can you separate azeotropes by distillation? how many compounds make up an azeotrope?

NO 2 or up

You are patiently waiting and suddenly notice the temperature jump and liquid condensing on the thermometer bulb or thermocouple— you should ________ .You should record the temperature when _____You should also record the temperature at which you ____

NOT TAKE TEMP HERE you notice liquid beginning to collect. take fractions

the vapor of an azeotrope has the ____ composition as the corresponding unboiled mixture

SAME

simple vs fractional distillation

Simple = larger differences in BP (100C+) (less specific)SEPARATING JUST TWO COMPOUNDS Fractional: EX: COMPONENTS OF CRUDE OIL - extra surface area with glass column BEFORE the condenser allows for multiple evaporation-condensation cycles - more surface area (glass beads) = more cycles

____ is frequently used to remove water from a sample. Water is ___ in this substance and the two _____ upon cooling. The substance is usually recycled.

Toluene insoluble separate

during evaporation, ____are being broken, not ____ bonds

Van der Waals interactions chemical/covalent

solvent safety?

Volatile and flammable , fire and inhalation hazard, keep distillation UNDER MINI HOOD

why do we vent the top of the apparatus and leave it exposed to open air?

a closed system will explode when heated and win you a lot of breakage charges

GC: the retention time, tr, is the amount of time it takes_______

a component to pass through the GC column.

you cannot state that an unknown liquid that____ is pure—it could be an )______.

boils at a constant temperature azeotrope

You ___ concentrate potable (drinkable) ethanol further than 95% by ____. There are other azeotropes using ____ that will form ternary azeotropes (three chemicals involved). These leave residues in the distillate. Distilled spirits are tested for the ______ specifically for this reason.

cannot distillation benzene presence of benzene,

The ____ of the components in the distillation of a mixture is called resolution. Resolution of mixtures is dependent upon three factors: _____. describe how each one affects resolution.

efficiency of the separation boil-up rate, reflux ratio, and number of theoretical plates slower boil up, larger reflux ratio, more tps

It takes a temperature difference of at least 25 °C between the distillate and the temperature in the condenser in order to get an ____of the vapor. When the temperature difference is less than 20 °C, a lot of vapor ___, regardless of the ____. Sometimes it is necessary to use ____ in the condenser to avoid the____

efficient condensation travels through the condenser, and escapes through the outlet. regardless of pressure chilled water loss of valuable product.

the vapor phase is constantly being ___ with the ___ boiling component as it rises up the distilling apparatus, and the liquid in the _____are being enriched in the higher boiling component.

enriched,, lower distilling flask and the liquid in the lower reaches of the column

the first clamp to the ring stand is shown connecting to the neck of the distilling pot. Do not place this clamp higher up on the fractionating column. This clamp acts as a ____and until you get the clamp hot, _____ It is easier to heat the jaws of the clamp if they are closer to the heat source.

heat sink no vapor will go past it. metal is cold, duh

As the vapor condenses, it ____ the apparatus and the condensation line continues to ____.

heats up rise toward the distilling head and the thermometer

the more times distillation occurs, the ____ the % A will become. Each of these condensation and vaporization (revaporization) steps is called a ______. The ____ theoretical plates that are present, the better the separation

higher theoretical plate more

a vapor-liquid composition diagram is for a mixture of two liquids, which behave as ___ liquids (no significant____ of the different liquids).

ideal interactions between molecules

2 ways to increase theoretical plate #

increase column length, decrease diameter up to 0.5 INCHES

Vapor pressure ____ with increasing temperature. Liquids with high vapor pressure ____and have a ____boiling point. Liquids with low vapor pressure will have a ___ boiling point. Materials with a very ___ vapor pressure are called nonvolatile.

increases evaporate easily / low high low-nonvolatile

GC is done using a tube with a steadily____that causes _____ bp compounds to flow through faster than___ bp compounds (like heptane), as a ___ going through the tube drags the compounds along. The GC was not exposed to water or acetone because these compounds could________ that allows gases to flow through.

increasing temperature lower, faster higher gas water has salts that can clog the columns, water absorbances will show up on the chromatogram and blur your peaks, water destroys the column over time, and can damage the detector and the pump that maintains the vacuum

the thermocouple should be put _____ of the assembly that the ____ will be collected in.

just below the lip condensate (the collection well)

The _____ the boiling point difference, the easier it is to separate two liquids,

larger

Fractional distillation is favored when the boiling point difference between the volatile components is___. Generally speaking, a difference of 10 °C is a realistic limit for fractional distillation. Fractional distillation is limited to ______samples because of the volume of condensate held up by the fractionating column. An occasional trick to overcome limitations owing to sample size is to add a -____ to the mixture. This higher boiling component can be used to ______ up the column.

less than 20 °C larger much higher boiling solvent sweep the valuable material

If thermocouple is too high, the recorded temperatures will be too ___. If it is lowered too much, the recorded temperatures will be too ____

low high

FOR DISTILLATION: the two liquids must be ______—otherwise we would have just used a _____to separate them—and ____ (evaporates at reasonably low temperature).

miscible (soluble in each other) separatory funnel volatile

bp drops because after pentane distills, the ___, so no hot vapor _______ to be recorded.

temperature is too low for heptane to evaporate contacts the Thermocouple

whats the difference between collecting fractions 1-3 vs #4?

the first 3 were collected during distillation while hot, the fourth was collected FROM THE DISTILLING FLASK (the bottom one) NOT the collection well,, after turning off the variac , mantle, removing the tiles, and letting the apparatus COOL

why was, the heating mantle was unplugged and left to cool after fraction 3? the glassware was NOT disassembled while hot...why?

to prevent boiling dry, which would cause thermal shock and shatter the glassware. could also shatter if opened up and exposed to the cooler room air (thermal shock).

why do we put the heating mantle on TOP of wooden blocks or a stir plate

to quickly remove it if the distilling flask starts overboiling violently

Over time, the amount of the most volatile component in the distillate increases T/F

true

Dispose of _______ in solid waste container under hood.

used Kimwipes/towels

What is boiling?

vapor pressure of liquid=atm pressure vapor starts collecting under liquid surface (BUBBLES)

The boiling point of a liquid is the temperature at which the ___ equals the ______and gaseous bubbles of the liquid will ______. (The initial bubbles observed when heating a pan of water are ______ solubility of a dissolved gas decreases with ____ temperature.)

vapor pressure//atmospheric pressure form below the surface of the liquid dissolved air being driven from the liquid; increasing temperature (INVERSE)

GC: describe the stationary phase

very HIGH boiling liquid adsorbed onto fire brick

Some organic materials are not sufficiently ____ at temperatures below their decomposition temperatures to be analyzed by gas chromatography (e.g., ____)

volatile polypeptides like enzymes---they will just break down at a high enough temp and not evaporate before then

The boil-up rate is the ______ + unit

volume of liquid that enters the column vapor per minute.

The reflux ratio is the _____ divided by ____. Larger values of reflux ratio ____ resolution. However, the larger the reflux ratio, the ___ will be required for the distillation. High reflux ratios are ___ to separate close boiling components.

volume of liquid that is returned to the pot divided by the volume of liquid that is removed as distillate increase more time NECESSARY

CLEANUP: Do NOT wash glassware with ____; rinse with -____ and only after _______ where do the first vs subsequent rinses go for disposal??? should we cap vials after cleaning?

water acetone, after it cools Catch first rinse and dispose in correct container under hood. Do second rinse into wash bottle in sink. NO, the stuff inside must evaporate so they can be reused