CHEM LAB FINAL

Eugenia caryophyllus

-clove -steam distillation of cloves results in oil. -made up of 85-90% of *eugenol* and 9-10% of *eugenol acetate*.

radical reactions

-covalent bonds undergo homolysis -homolysis: bond cleavage in which both atoms contain one electron

Halogenation

-creates vicinal dihalides, bc two halogen groups are attached to adjacent carbon -undergo electrophilic additions -Br2 and Cl2 are commonly used bc they occur rapidly in room temperature.

rules of classification tests

-performs the test exactly as described. -always perform test on a known compound that will give you a positive and negative test to help for comparision

for the grignard lab, how do you relieve the pressure inside a reaction tube

-pierce the septum cap with another syringe needle

in the grignard lab, what do you do if you need to control a reaction

-place it in an ice bath

in the unknown alcohol lab, explain the TCICA test

- reacts fastest with *primary and secondary* alcohol. -positive test when precipitates from from the acetonitrile

in the grignard lab, how do you extract water from solutions

-*diethyl ether* must be used, or ordinary ether (used for the extraction of aqueous solutions

in lab 5, how did we isolate p-tert-butylphenol

-*heat up* the NaOH extract to remove any traces of *tert-butyl methyl ether* that could inhibit crystallization -also add 3M HCl until acidic -cool in ice bath to facilitate crystallization -vacuum filtration

physical properties of hydrocarbons

-*insoluble* in water, so they mix well in nonpolar solvents (CCl4,CH2Cl2) -*less dense* than water, so they float

results of Lucas test

-*tertiary alcohols*: gets cloudy in less than 30 secs -*secondary*: gets cloudy in 1-3 minutes -*primary*: takes an hour to react

explain the bromine test in the dehydration lab

-Bromine test is performed on the alkene sample, methylene chloride and bromine and the color disappeared because it reacted with the double bond

why you should not distill to dryness

some organic compounds can explode when heated to dryness

how does the flow rate of the gas through the columns affect the rate at which compounds travel through the GC system

speeding up the gas flow increases the speed with which all compounds move through the column

salting out

extraction of polar compounds into nonpolar solvents -Ex: inorganic salts, like NaCl, are dissolved in water to reduce the solubility of the organic compound in the aqueous layer

Name two reasons why it is sometimes difficult to measure the temperature at which the crystals first begin to liquefy.

If a small amount of impurities are present the liquid produced is small and hard to detect, sweating from solvent still in the sample, and a change in the shape of the sample due to heating.

why do aromatic compounds resist addition reactions

-bc of their aromaticity

SN1 reaction mechanism

2 Step reaction where the LG leaves and creates a carbocation then the nucleophilic attack -give a racemic mixture (enantiomers )

if you mistakenly extracted the ether solution first with NaOH solution and then with NaHCO3 solution, no crystals would be produced upon acidification of the NaHCO3 layer. Briefly explain

NaOh is a base solution, so it will remove the acidic compound from the ether,which leaves no more to be extracted with NaHCO3.

Two methods of visualizing TLC plate

Under UV light or in iodine chamber

Fractional distillation

Used to separate compounds that have a boiling point difference that is less than 40 degrees -a fractionating column is placed between the pot and distilling head. -

Developing a plate

Using filter paper we put the plate in a developing chamber with eluent. The filter paper will absorb the eluent and ensure the atmosphere is saturated in vapor.

Essential oil

Volatile compound that is used as a flavoring/perfume and is derived from plants

racemic mixture

a mixture of equal amounts of two enantiomers

why you should not heat organic solvents over a bunsen burner flame

because organic solvents may catch fire, they are potentially flammable.

emulsion

a suspension of small droplets of one liquid into the other liquid after shaking. -usually gives an opaque/ cloudy look -can also be mistaken for a third layer -can be fixed by swirling of container, adding a few drops of more solvent to dilute the solutions

volatile

compounds that have relatively high vapor pressures and low boiling points -distillation is used to remove the volatile solvent from a nonvolatile product, to separate a volatile product from nonvolatile impurities, or to separate two or more volatile products that have sufficiently different boiling points.

recrystallization

is a purification process used to remove impurities from organic compound that is solid at room temperature. -this process is based on the premise that the solubility of a compound in a solvent increases with temperature. -when it comes to choosing the solvent the compound must be very soluble in the chosen solvent. -the boiling point of the recrystallization solvent should be lower than the melting point of the compound to be recrystallized.

how does volatility of compounds affect the rate at which compounds travel through the GC system

low-boiling components will travel faster than components with high boiling points

at the end of the grignard reaction, what should be the melting point of your final product

no lower than 160

ionic reactions

occur when one atom donates an electron to another atom, thereby becoming a positive ion, while the other atom attains a negative charge. -undergoes heterolysis: cleavage of a bond in which both electrons are given to the same atom

Evaporation

occurs at a temperature below the boiling point of a compound, involves the transition from liquid to vapor of only those molecules at the liquid surface. -the pressure exerted by these gaseous molecules on the walls of the container.

Nucleophilic substitution

rxn in which the halide is replaced by another group

saturated vs unsaturated hydrocarbons

saturated: alkanes unsaturated: alkenes and alkynes -aromatic: cyclic hydrocarbons

How would the results differ if you added sodium p-toluate instead of p-toluic acid to the two-layer mixture of tert-butyl methyl ether and water?

sodium p-toluate will be found in the water layer because it is more soluble in water than tert-butyl methyl ether.

What solvent was suitable for separation of two polar compounds using silica gel

toluene or ethyl ether

In SN1 reactions, the intermediate carbocations can eliminate a proton to yield what byproducts?

Alkenes through elimination reactions (2 products), and ethers.

percent recovery equation

% recovery = mass of pure solid after recrystallization / mass of impure solid before recrystallization x 100

results of the TCICA test

- *secondary* alcohol reacts in less than 30 secs - *primary* alcohol reacts within 3-7 minutes -*tertiary* alcohols do not react at all

SN1 reactivity

- 3° > 2°> 1°> CH3X ( the alkyl groups stabilizes the charge by displacing electrons towards the positive charge) -LG: I > Br > Cl > >F -favors high polarity -favors low concentration of nucelophile

during lab5 (extraction lab), what did we do to remove any toulic acid remaining in the ether layer

- add a second NaHCO3 to the tube of the ether mixer, then extracted the aqueous layer and combine it in the beaker with the first extract.

in the unknown alcohol lab, explain the Lucas test

-*tertiary* alcohols react the *fastest* and primary the slowest. -This reaction is an *SN1* reaction. *HCL* is used to replace the *OH*- w/ *Cl-*. -The Lucas reagent is Zncl2 in HCl. - a positive test is when the nonpolar alkyl halide formed in rxn begins to separate and forms two layers -for the Lucas test to work, the alcohol must be soluble in aqueous ZnCl2 solution (alcohol can not contain more than 7 carbons)

hydrocarbons

-Compounds composed of only carbon and hydrogen

precautions for Grignard reagent

-The starting material for Grignard reagent *MUST NOT* have any acidic protons -all *equipment and reagents (magnesium/ether)* must *absolutely dry*, which can be dried in a 110-degree oven for 30 min -*plastic and rubber* components should be *rinsed with acetone* if they appear to be dirty or wet with water, then place in a desiccator for at least 12 hours.

simple distillation

-Used to separate a liquid from a solution when the difference of boiling points are large

combustion reaction

-a chemical reaction that occurs when a substance reacts with oxygen, releasing energy in the form of heat and light - products are carbon dioxide, water and heat

Gas Chromatography

-a method of analyzing the components of a mixture -used as analytical tool rather than a means for purification

Stationary phase of chromatography

-a polar absorbent -nonpolar molecules tend to stay in mobile phase -the more polar the functional group the stronger the absorption in the stationary phase and the more slowly the molecules will move. -silica gel is the most common column used for chromatography

Distillation

-a technique that can be used to physically separate most homogeneous mixtures based on the differences in the boiling points of the substances -the vapor that is produced through distillation is cooled then reliquefied by passing through a water-cooled *condenser* and collected in a *receiver*.

percent yield equation

-actual yield/theoretical yield x 100 -*percent yield* = (amount recovered/ original amount) x 100

in the hydrocarbon lab, what do you do when during the bromine reaction you get a negative test after adding 10 drops of the bromine solution

-add 5 more drops of 1% Bromine and small amount of ZnCl2

in lab 5, how did we isolate acetanilide

-add Na2SO4 remaining ether layer in separatory funnel to removes all traces of water from solution -heat solution to evaporate the ether (oil will remain) -crystalised the oil remaining (the acetanilide) by cooling in ice bath -

during the grignard reaction, if the volume of ether decreases what do you do

-add more anhydrous ether, bc the solution of Grignard reagent deteriorates on standing

how to lessen the chances of biphenyl forming

-add the bromobenzene slowly to the reaction mixture so it will react with previously formed grignard reagent. -the impurity is easily eliminated bc it is much more soluble in hydrocarbon solvents then triphenylmethanol

in lab 5, how did we isolate p-toluic acid from the NaHCO3 extract

-added 3M HCl to make it more acidic -then used vacuum filtration

in the hydrocarbon lab, explain the reaction with concentrated sulfuric acid

-addition reaction with sulfuric acid -products become soluble in H2SO4 -saturated and aromatic compounds are unreactive -alkynes react slowly and require a catalyst

in the hydrocarbon lab, explain the reaction with potassium permanganate

-alkanes and aromatic compounds are generally unreactive -reaction occurs when the loss of purple color and brown precipitate

in the dehydration lab, what did we do with the results from the GC

-alkene sample was dissolved in Pentene and the 5ul was added to GC. -used the results to find: --*peak area* = Height x width @ 1/2 height --*percent area* = (peak area/ total area) x 100 --*percent yield* = (amount recovered/ original amount) x 100

in the hydrocarbon lab, explain the reaction with bromine

-an addition reaction with bromine -bromine is red, a reaction has taken place when there is a loss of color from the bromine solution and remains colorless -this usually happens with unsaturated hydrocarbons

microscale distillation

-are used when small volumes of liquid must be purified for spectral or refractive index analyses

Why might it be very difficult to visualize the separation of cis- and trans-2-butene by TLC?

-bc they are the same functional group, so they are very similar in polarity and will look very similar on the plate

qualitative tests used to characterize the clove oil

-bromine: red to colorless -potassium permanganate: purple to brown -Phenol( iron(III) chloride) : yellow to complex colors

versatility of Grignard reagent

-can undergo 13 different reactions - in every reaction but 1, the intermediate alkoxide must be hydrolyzed to give the product.

as molecules move up a fractional distillation column, they condense and then revaporize. During which of these steps is the concentration of the more volatile compound of the mixture increased

-during revaporization because the vapor will contain a large amount of the more volatile compound. since it tends to vaporize more than the non-volatile compound

In the halogentation lab, why isn't fluorine or iodide favorable for halogenation

-fluorination is a violent reaction that is hard to control and is usually accompanied by several side reactions -iodination is an endothermic process that reverts alkenes

what two visible evidence of reaction will you see when you acidify the NaHco3 extract with HCl solution

-foaming -precipitate of toluic acid

grignard with aldehydes and ketones

-gives a primary, tertiary and secondary alcohols

in the nucleophilic substitution lab, what happens when you put sodium iodide in acetone

-gives an SN2 reaction, bc acetone is a nonpolar solvent it will dissolve sodium iodide and will not ionize the the alkyl halide.

distillation rate

-important factor in separation of compounds -if distillation is conducted too fast, liquid-vapor equilibria will not be established in the fractionating column, and poor separation of the compounds will result.

for the grignard lab, how do you remove ether from a septum-capped bottle

-inject a volume of air into the bottle that is equal to the amount of ether being removed -pull out more ether than needed into the syringe -push the excess back into the bottle before removing the syringe, so there are not bubbles in the syringe and it will not dribble.

Grignard reagent

-is a strong base and strong nucleophile -As a base it reacts with all protons that are more acidic then those in alkenes and alkanes. Thus, it will react with water, alcohols, amines, thiols to regenerate an alkane. -Grignard rxn is a C-C bond forming rxn by which any alcohol may be formed from alkyl halides and carbonyl compounds.

why should you not overheat magnesium

-it can become deactivated through oxidation, or if strongly overheated, it can burn

in the grignard lab, how is the impurity biphenyl formed

-it is formed when phenylmagnesium bromide reacts with unreacted bromobenzene

why is the fractionating column positioned vertically

-it is positioned vertically to *promote mixing of liquid and vapor phases*. -the outer jacket insulates against heat loss from the inner jacket during distillation. (DO NOT PASS WATER THROUGH FRACTIONATING COLUMN) -wrap the fractionating column and distilling head with aluminum foil to minimize the temperature fluctuations

why do compounds need to be finely ground

-it packs better into the capillary and also if the particles are too chunky then they don't pack well and causes air pockets which slow heat transfer.

in the unknown alcohol lab, if the derivative does not dissolve in the ethanol what do you do

-keep adding 1 mL more of ethanol and continue heating. -DO NOT EXCEED 5 mL of extra ethanol

Why is it necessary to run TLC in a closed container and to have the interior vapor saturated with the solvent?

-keeps interior saturated -if solvent evaporates it will take longer for spots to travel up he plate -lower Rf values.

in the grignard lab, what are the advantages of keeping anhydrous diethyl ether in a 50 mL septum capped bottle

-keeps the ether anhydrous -exposure to oxygen is minimized -little possibility of it catching fire (*ether is extremely flammable* )

how was the derivative created

-mixed 3,5-dinitrobenzoyl chloride with our unknown in test tube and heated it up for 10-15 min. -let cool in room temp to solidify, not solidified in 5 min put in ice bath for 5 min so crystals can from. (*if no crystals form, add 3,5-dinitrobenzoyl chloride, 4-dimethylaminopyridine, acetone, and your unknown. heat up until acetone boils, then allow to cool at room temp then place in ice bath.

if the grignard reaction beings very slow or later becomes slow what do you do

-mount the flask and condenser in a heating mantle or thermowell and reflux gently until the magnesium has disintegrated and the solution has acquired a cloudy or brownish appearance

derivatives

-new compounds -these can be used to identify unknowns by comparing melting points to known literature values -we used *3-5-dinitrobenzoate ester* -however, *tertiary* alcohols react slow bc of steric hindrance, so we use *DAMP* as a catalyst.

how to assess the purity of the recrystallized compound

-observing its color (if off-white color recrystallize again using activated carbon) -measuring its melting point (pure is melting point range is narrow like 1-3 degrees)

grignards with carbon dioxide

-occurs readily to produce a carboxylic acid

grignards and epoxides

-opens the ring and yields an alcohol

SN2 reactivity

-opposite of the carbocation -methyl> 1°> 2° -why not 3°, bc of steric hindrance -LG: I > Br > Cl > >F -faster reaction in a nonpolar and aprotic solvent -favors high concentration of nucleophile

during distillation, why is it important to select a good pot size

-overfilling the pot can result in bumping and foaming of material into the receiver.

in the nucleophilic substitution lab, when testing the groups and no reaction occurs with in the the first 5 minutes, what do you do?

-place the tubes in a 50°C water bath and watch to see if a reaction occurs for the next 5-6 mintues

how does polarity affect the rate at which compounds travel through the GC system

-polar compounds will move more slowly

in the unknown alcohol lab, if the cooling derivative ethanol solution starts to turn cloudy and turn to liquid what do you do

-put the test tube in an ice bath to allow recrystallization to continue

how does the temperature of the column affect the rate at which compounds travel through the GC system

-raising the column temperature speeds up all the compounds in the mixture -this is the easiest factor to change

for the grignard lab, when do you know it is a good stopping point for the reaction

-refluxing the mixture for 30 min or stoppering the flask with calcium chloride tube and letting the mixture stand overnight

washing

-reverse process of extraction -impurities are removed from the second solvent layer, leaving the desired compound in the original solvent.

chemical reactivity of hydrocarbons

-saturated hydrocarbons: generally unreactive to most reagents -unsaturated hydrocarbons: will burn and react by addition of reagents to the double or triple bond, but very slowly -aromatic hydrocarbons: will burn with a sooty flame, bc of the high carbon-hydrogen ratio (will undergo substitution reaction)

the strength of attractive forces depends on the following factors

-size, polarity, and hydrogen bonding ability of molecules A and B

characteristics of carbocations

-sp2 hybridized -trigonal planar -there is a vacant p-orbital - 3° > 2°> 1° ( the alkyl groups stabilizes the charge by displacing electrons towards the positive charge)

after grignard reaction is finished why do we add 10% sulfuric acid and sodium chloride

-sulfuric acid: to remove any further traces of magnesium salts -sodium chloride: to remove water that has dissolved in the ether

classification test

-support or refute the presence of certain structural features of a molecule -results of the tests are readily visible, like color change, percipient, gas or layer separation

why should you not heat the clove mixture too rapidly

-the clove mixture tends to foam when heated to quickly

criteria for selecting a solvent for recrystallization

-the compound being purified must be insoluble in the solvent at room temp. -the compound must be soluble in boiling the solvent -solvent's boiling point must be lower than the compound's melting point -an abundant quantity crystals must be recoverable from the cool solvent. *** usually one solvent will meet the criteria, but if more than one does then they are called solvent pairs. pairs must be miscible and should have opposite abilities to dissolve. (compound is soluble in solvent A and insoluble in solvent B)

in the dehydration lab, when you dehydrated cis and trans 2-methylcyclohexanol with phosphoric acid what were the products

-the major product was 1-methylcyclohexene -small amount of 3-methylenecyclohexane -sometimes a E2 Hoffman product is produced as a very minor product

theoretical yield equation

-the maximum amount of product that can be produced from a given amount of reactant -EX: *Multiply the number of moles of the product by the molecular weight of the product* to determine the theoretical yield. For example, if you created *0.5* moles of Al2O3, the molecular weight of Al2CO3 is *101.96* g/mol, so you would get *50.98 grams as the theoretical yield*.

How is a Grignard reagent prepared?

-the reaction will begin at the exposed surfaces -this evident by *slight turbidity*(how clear the solution is) in the solution and evolution of *bubbles*. -once the exothermic reaction starts, it proceeds easily, the magnesium dissolves and a Grignard reagent is formed.

when preparing the grignard reagent what does it mean if the solution is turbid or gray

-there are impurities in the magnesium

What do boiling chips do?

-they provide a surface on which vapor bubbles can form. This bubble formation helps prevent superheating and bumping of the liquid. -do not add boiling chips to hot liquid, the large surface area of the boiling chip can cause the hot liquid to foam out of the apparatus and cause burns

when color is produced during recrystiallization

-this means that the sample may contain impurities -activated carbon can be used to remove these impurities from the solution. just adding carbon itself can absorb the compound that is being crystallized = reduces percent recovery

what will happen if you increase the heating rate during distillation

-this will cause most of the liquids to boil at the same time. Therefore, liquid vapor equilibria can not be reached during distillation. In result, there will be poor separation of compounds

why is the funnel, filter paper, and collection flask heated with boiling solvent

-to prevent premature crystal formation.

in lab 5, why did we continue to add NaHCO3 to the ether solution in the separatory funnel

-to remove any p-toluic acid remaining in the ether layer.

why did we add sodium sulfate (Na2SO4) to the ether extract

-to remove any traces of water from the ether extract -after Na2SO4 absorbs the water it will look like salt/sugar

What will be the appearance of a TLC plate if a solvent of too low polarity is used for the development? A solvent of too high polarity?

-too low polarity: spot won't travel much -too high polarity: spot will run off plate

sweating

-traces of solvent may present may be present due to insufficient drying and my appear as droplets on the outside surface of the sample

in lab 5, what solvents were used to extract what

-used NaHCO3 to extract p-toluic acid from ether solution -used NaOH to extract p-tert-butyl phenol from ether solution -used NaSO4 to extract acetanilide from ether this removes traces of water from

in the dehydration lab, how was water removed in solutions

-via an acid, and once it was removed a c=c bond was able to form

in the nucleophilic substitution lab, how did we test the effect of the solvent on the rate of SN1 reactivity

-we compared the time needed for precipitate to appear when 2-bromobutane was treated with the 1% ethanol silver nitrate and then the 1 % silver nitrate in a mixture of 50% ethanol and 50% water

in the nucleophilic substitution lab, what happened with the ethanolic silver nitrate solution

-when an alkyl halide is treated with ethanolic silver nitrate, the silver ions coordinate with an electron pair from the halogen. This weakens the carbon-halogen bond bc the molecule of insoluble silver halide is formed, thus promoting an SN1 reaction -ethanol favors ionization of the halide and the nitrate ion is a very poor nucleophile

in the grignard lab, how do you prevent ether from boiling away

-wrap a pipe cleaner around the top part of the reaction tube. -dampen the pipe cleaner with water or, if room temperature is very hot, with alcohol.

SN2 reaction mechanism

1 step reaction where the nucleophile attacks at the same time the LG leaves -results in one inversed product

How gas chromatography works

1)The sample is injected to the helium using a microsyringe 2) The helium and sample move through the oven 3)This vaporises the sample 4)Helium and the gaseous sample move into a polymer collum 5)Particles in the sample are attracted differently to the collum, affecting how fast they move through it 6)This leads them to exit at different times 7)The chromatogram shows the amount of time taken for each substance to pass through,the amount and what the substances where in the mixture.

2 steam distillation methods

1)adding excess water to the compound of interest in a distilling flask. then heat mixture to boiling. the resulting vapor is condensed and collected in receiving flask. compound is then separated from water by extraction 2) steam is bubbled into the compound of interest to affect the distillation.

Sublimation

A change directly from the solid to the gaseous state without becoming liquid

Electrophilic addition

A type of addition reaction in which an electrophile is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond.

Prevent premature recrystallization in the funnel stem during gravity filtration

Add 5% excess solvent to the saturated solution

Codistillation

Distillation of two immiscible liquids

steam distillation

Distillation when one compound in a mixture is water -offer an advantage in the volatile compounds that are unstable or have high boiling points can codistill with water at a relatively low temp. -this helps to avoid decomposition that might occur at the normal boiling point of the compound of interest.

in the grignard lab, If the ethyl benzoate used to prepare triphenylmethanol is wet, what byproduct is formed?

Ethyl benzoate + 2 phenylmagnesium bromide --> triphenylmethanol•MgBr salt if water is present, the grignard reacts with the water first Phenylmagnesium bromide + H2O --> benzene + MgOHBr

in the nucleophilic substitution lab, The addition of sodium or potassium iodide catalyzes many Sn2 reactions of alkyl chlorides or bromides. Explain.

Iodine is a very good leaving group, so it leaves the sodium/potassium very easily. Once iodine is formed, it can act as a good nuceophile to remove the Br or the Cl.

Spotting a plate

Marking the origin and drawing a line on the bottom of the plate, then the sample compound is dissolved in a volatile solvent.

eutectic composition

The composition of the liquid phase that reacts to form two new solid phases at the eutectic temperature.

The more polar an eluent is the...

The greater its eluting power and ability to move compounds over the absorbent surface

eutectic temperature

The lowest temperature at which a mixture of two elements will completely melt.

Orientation melting point

The melting point at which the sample is heated 10-15 C until it melts and then cooled to 15 below the "orientation melting point"

The more polar a compound from a mixture is...

The more strongly it adheres to the polar adsorbent and the slower it moves

distillate

The more volatile liquid collected in the receiver during distillation when the evaporated substance condenses -Liquid in part E

Eluent front

The point that the eluent has reached

in the nucleophilic substitution lab, What would be the effect of carrying out the sodium iodide in acetone reaction with the alkyl halides using an iodide solution half as concentrated?

The reaction rate would be halved. It would occur half as slow.

Why is it important to heat a sample slowly to obtain an accurate melting point?

To allow temperature recorder to have time to be accurate before melting actually occurs.

in the grignard lab, What is the purpose of the ether extraction?

To isolate the organic compound

extraction

a process that selectively dissolves one or more of the mixture compounds into an appropriate solvent. The solution of these dissolved compounds is often referred to as the *extract* -it transfers compounds from one liquid solvent to another liquid solvent -compound can be separated form impurities in a solution by extractiong the compound from the original or first solvent and into a second solvent. -the compound myst more soluble in the second solvent than the first solvent, and the impurities must be insoluble inthe second solvent. -for larger extrations use a separatory funnel, and for microscal extrations use a test tude or a centrifuge tube

A student rushed through this experiment. Describe the effect that the following procedural changes would have on percent recovery of acetanilide. Briefly explain the basis of each answer. a) Rather than adding 0.5-mL portions of boiling solvent to the acetanilide, the student added 5-mL portions of boiling solvent. b) The student did not preheat the gravity filtration apparatus in Part 3. c) The student forgot to cool 5 mL of solvent in Part 5 and washed the crystals with room-temperature solvent.

a)Because of more dilution the formation of crystal rate is slow b) Hot gravity filtration is used to separate insoluble impurities from a hot solution. Hot filtrations require fluted filter paper and careful attention to the procedure to keep the apparatus warm. As you are not preheated apparatus, you will end up with impurities along with desired product. c) Using room temperature solvent some amount of crystals will dissolve with solvent and student will get less yield of product.

Dalton's Law

at constant volume and temperature, the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the component gases -When two immiscible liquids are distilled and the total vapor pressure above the liquid is equal to the sum of the vapor pressures of each compound

In the halogentation lab, how is bromination different in electrophilic addition

bromination different in electrophilic addition -in the first step, instead of there being a carbocation formation during the intermediate a bromonium ion is what attacks partially positive charged carbon and stabilizes it. -Br can act as both an electrophile and nucleophile -anti-addition bc Br- is blocked from one face of bromonium ion by the bromine atom. -forms two new chiral centers

meso compound

contains a chiral center but has a line of symmetry

Elimination rxn

dehydration of alcohols to give alkenes

Rf value equation

distance moved by substance/distance moved by solvent

Equation for Rf

distance spot travels/ distance solvent travels

theoretical plate

each condensation and revaporization that occurs on a fractionating column

Suppose that you used dichloromethane instead of tert-butyl methyl ether as the nonpolar solvent in this experiement. What changes in the procedure would you make in view of the fact that dichloromethane is more dense than water.

extract the bottom layer and save it. then get rid of the aqueous top layer left in the funnel

The more polar an eluent the...

greater the eluting power/ability to move compounds through the adsorbent

why is the dissolved compound in the boiling solvent cooled to room temp before vacuum filtration

if crystals formation happens too rapidly, impurities can get trapped in the crystal -so cool the solution in an ice bath and crystals will slowly form, if not you can scratch the inside of the glass or the compound can be placed in a solution (ice bath) to promote crystal growth

oiling out

is something that occurs when a compound is insoluble in a solution at a temperature above the compound's melting point, -as a result, the compound is deposited as an oil and not crystals. -prevent: ensure the boiling point of the recrystallization solvent is lower than the melting point of the compound to be recrsytallized

immiscible

liquids that are not soluble in each other -produce two separate layers -we vigorously mix to get the compound to transfer over to the other layer. -after separation is complete, the compound will be in the desired layer and the impurities will remain in the first layer. -one layer is usually water (polar) and the other layer is usually nonpolar, like a hydrocarbon, ether, or chlorinate (dichloromenthane) -the more dense product is at the bottom (can use the water drop test to see which is the aquecous layer)

In the halogentation lab, why don't cis-stilbene, trans-stilbene, and pyridinium tribromide dissolve in acetic acid right way?

solid materials are not soluble at room temp in acetic acid

What error is introduced into the determination of an Rf value if the top is left off the developing chamber?

solvent will evaporate and affect the Rf value

What will be the result of applying too much compound to a TLC plate?

spots will become to large and it can end up merging with other spots when traveling

how does the length of the column affect the rate at which compounds travel through the GC system

the longer the column, the longer it will take all the compounds to eluate. longer columns are employed to obtain better separation.

what product would you obtain if you evaporated the water from the NaOH layer prior to acidifying the layer?

the salt of p-tert-butylphenol

Chromatography

the separation of two or more compounds or ions caused y their molecular interactions with two phases ( moving and stationary) -the stationary phase is usually a polar solid absorbent -mobile phase can be a single solvent or a combination of solvents

melting point

the temperature at which the solid is in equilibrium with its liquid -the presence of impurities always causes the melting point to decrease -helpful in identifying an unknown compound and the purity of a compound (if range is greater than 5 degrees then is impure, pure if rand is 1-2 degrees)

boiling point

the temperature at which the vapor pressure of the liquid is equal to the external pressure (atmospheric pressure) applied to the surface of the liquid.

Raoult's Law

the vapor pressure of a solution is directly proportional to the mole fraction of solvent present

miscible

two liquids that are soluble in each other and form a homogeneous solution -the mixture will boil at a temperature between the boiling points of the pure compounds.

unknown alcohol lab

used qualitative tests called classification tests and derivatives to identify to identify an unknown alcohol

how does polarity of the column packing material affect the rate at which compounds travel through the GC system

usually, all compounds will move more slowly on polar columns, but polar compounds will show a larger effect

What problem will ensue if the level of the developing liquid is higher than the applied spot in a TLC analysis?

whatever is being analyzed will dissolve in the solvent and won't travel up the plate

melting point range

when the crystals begin to liquefy to the point at which the entire sample is liquid