orgo post and pre lab

purpose of melting point experiment

The purpose of this experiment is to learn a technique for determining the melting point and figuring out the eutectic point of a mixture of cinnamic acid and urea, and identifying the unknown. 

Where do the following items need to be disposed after carrying out the melting point experiment? melting point capillary after use

sharps container

Where do the following items need to be disposed after carrying out the melting point experiment? disposable test tube

broken glass container

Where do the following items need to be disposed after carrying out the melting point experiment? used weighing paper

regular trash

Where do the following items need to be disposed after carrying out the melting point experiment? leftover solid organic compound 

solid chemical waste 

Order the steps for PACKING a solid sample in a melting point capillary BEFORE placing it in the melting point apparatus.

ensure sample dry and finely powdered, create a pile of sample, force open end of melting point capillary into sample, tap closed end of melting point capillary on hard surface, ensure sample height is 2 to 3mm

Order the steps for DETERMINING a melting range for a solid sample AFTER placing it in the melting point apparatus.

increasing heating rate, slow heating rate, note first drop of liquid in sample, not lower temperature of melting range, not when entire sample is melted, note higher temperature of melting range

When comparing 2 hydrocarbons, the smaller, lower molecular weight molecule would have ____________ melting point because of _______________

lower, decreased attractive forces

ou come across a white solid and take its melting point and find it to be 104-107°C. You decide to identify it. If the thermometer is calibrated, compounds of what general melting point range can you automatically eliminate? What is the reason you can eliminate the range you indicate in part (a) ?

above 107 degrees, impurities can only lower melting point 

The fast determination of the first sample of your unknown shows the unknown melting around 112C.

At what temperature should you slow down the rate of heating to 1C/min?

at 102 degrees

You have to pick two standards that could be your unknown because you don't know if thermometer calibration is an issue - the first standard MUST be listed alphabetically before the second standard 

acetanilide, m toluic acid

If your unknown is indeed the alphabetically second standard that you chose, what would happen to the mixed melting point of your unknown +this standard?

melting pint stays the same

Based on the result above, what would happen to the mixed melting point of your unknown + the alphabetically first unknown that you picked? melting point goes down, What is the identity of your unknown?

m toluic acid

recrystallization purpose

The purpose of this lab is to learn techniques of recrystallization and to compare two methods of crystallizing whichever solid you are assigned. 

boiling stick purpose

to prevent superheating

How do you increase heat to the part of the test tube labeled A?

move test tube deeper into the sand bath

In the solvent pair experiment that is being carried out with the solid that is being recrystallized, why do you NOT have to worry about sudden vigorous boiling of crystal solution when you add the second solvent to the solution?

second solvent has higher boiling point then first solvent

Where do the following items need to be disposed after carrying out the recrystallization experiment? glass pipetter after use

sharps container

Where do the following items need to be disposed after carrying out the recrystallization experiment? disposable test tube

broken glass container

Where do the following items need to be disposed after carrying out the recrystallization experiment? used filter paper

normal trash

Where do the following items need to be disposed after carrying out the recrystallization experiment? ethanol filtrate 

solvent/ liquid waste 

Order the steps of the DISSOLVING THE SOLUTE stage of the recrystallization of a solid in a single solvent

boiling solvent, add 2 to 3 drops of hot solvent to solid in test tube, add boiling stick to test tube with crystal solution, heat solution with boiling stick while adding hot solvent until solid dissolves, remove boiling stick

Order the steps of CRYSTALLIZING THE SOLUTE stage of the recrystallization of a solid in a single solvent

wrap test tube with hot crystal solution with paper towel, let crystal solution cool to room temperature, place crystal solution on ice

Order the steps of COLLECTING AND DRYING THE SOLUTE stage of the recrystallization of a solid in a single solvent

filter formed crystals using a hirsch funnel, wash crystals with ice cold solvent, let crystals dry on hirsch funnel for few minutes, squeeze crystals with filter paper, let crystals air dry on watch glass

You are given a unknown white solid to recrystallize in lab. The white solid could be Compound A (melting point 160-162°C), Compound B (melting point 110-111°C) or Compound C (melting point 141-142°C). Compound A, B and C are significantly soluble in n-butanol (bp: 125°C), even at room temperature and not very soluble in water (bp: 100°C) or ethanol (bp: 78°C) (difference in solubility of solid in water and ethanol is not significant) .

N-butanol is miscible with ethanol but not with water.  

If you decide to use n-butanol (must use this solvent) and choose between ethanol and water as the solvent pair for the unknown white solid, describe which solvent you would heat up and dissolve the solid in initially———- and which solvent you would add second ethanol and at what point would you stop adding the second solvent ————

ethanol, first signs of cloudiness

distillation purpose

The purpose of this experiment is to learn techniques of distillation and compare the simple and fractional distillation of cyclohexane and toluene mixture. 

What is the vapor pressure of a sugar solution dependent on?

the number of water molecules present in a given volume

You have  a 1:1 mixture of 2,2,4-trimethylpentane (boiling point: 99C) and methoxybenzene (boiling point: 154C) that you wish to separate. 

a) What common criteria would this mixture have to satisfy in order to be separated by either simple or fractional distillation?

homogenous

You have  a 1:1 mixture of 2,2,4-trimethylpentane (boiling point: 99C) and methoxybenzene (boiling point: 154C) that you wish to separate. What kind of distillation (between simple and fractional) would be efficient for this mixture?

fractional 

You have  a 1:1 mixture of 2,2,4-trimethylpentane (boiling point: 99C) and methoxybenzene (boiling point: 154C) that you wish to separate. Why would the distillation type chosen in question b) be ideal for this mixture?

boiling point difference and composition

From figure 5.8 on (Chap. 5: Sect 5C), you distill a liquid mixture of 50% ethanol: 50% water. What would the temperature when the distillate begins to condense in the sidearm (the distillate’s boiling point) be?

79 C

f you boiled the liquid mixture of 30%cyclohexane and 70% toluene, condensed the vapor mixture it generated and then redistilled that condensed mixture, what would the vapor composition of the mixture resulting from the 2^nd distillation be?

75% cyclohexane: 25% toluene

What is the character of the vapor after each condensation-vaporization cycle in a fractional distillation of a mixture?

Vapor is richer in the more volatile fraction

What specifically causes the vaporization of the lower boiling liquid on the packing in a fractional distillation?

heat released by condensation of higher boiling vapor

In vacuum distillation, how you do ensure that the liquid does not boil too suddenly upon reduction of pressure?

heat flask only after system has been evacuated

Why would boiling stones not be able to control the bumping of liquids in vacuum distillation as they are able to for simple and fractional distillations?

Boiling stones lose their activity in an evacuated system

What aspect of water makes it favorable to use in steam distillation?

its low molecular weight

Before spotting on TLC plate:

Draw line 5 mm from top of plate with pencil, Draw line 1 cm from bottom of plate with pencil

Before placing spotted plate in developing chamber

Place filter paper in developing chamber, Add eluent to level of 4mm high in developing chamber

During developing:

Keep cover placed on the developing chamber, Wait for solvent to just reach top pencil line on plate before removing plate from chamber

During visualizing:

Shine UV light on TLC plate, Trace spots with pencil while UV light is shining on the plate

Define the term adsorbed it relates to the states individual components can exist in for the TLC process.

Adsorbed means sticking to the surface of the solid stationary phase. 

What is the purpose of having very small bores on the spotters?

 So liquid does not flow out as a drop once it is drawn in

Besides a large spot and the TLC sample being too concentrated, what two other factors can cause the developed spots to appear as a streak?

sample having too many components that run together or using certain solvent

Other than solubility of sample in the solvent, what is the criteria for the solvent (other than cheap and nontoxic) used for preparing the sample that impacts the experiment?

volatile

Why would this criteria be important in the spotting phase if you have to make repeated applications of the sample? So that the solvent __________________Dissolves the complete sample to ensure the spot of the sample is ________________

dissolves the complete sample, is not too big

Why would water not be used to elute a column (besides it polarity) in column chromatography?

It would dissolve the silica gel in the column

n column chromatography (microscale), after loading it with solvent and adsorbent and prior to loading the sample, what level should you allow the solvent to drop to?

5mm above the top of the column packing

What features will appear in the column if you allow the column to run dry?

formation of air bubbles and channels

What is the consequence if you do allow the column to run dry?

Poor separation

Rank standards from Plate from Least to Most Polar:

aspirin, acetaminophen, caffeine 

Let's consider that ethyl acetate is the ideal solvent for this TLC experiment. What might have happened to the spots if you had used t-butyl methyl ether (MTBE) as the eluent instead of ethyl acetate. and WHY

Spots remain towards bottom of TLC plate, t-butymethyl ether less polar, cannot overcome attractions of sample to adsorbent

Let's consider that ethyl acetate is the ideal solvent for this TLC experiment. What might have happened to the spots if you had used acetone as the eluent instead of ethyl acetate.

and WHY

Spots move towards top of TLC plate, acetone more polar, overcomes attractions of sample to adsorbent better

The reason the TLC could not be visualized by UV is because:

The products are not conjugated

The reagents KMnO₄ in base  forms the less polar diol - what is the product?

cis-diol

The reason both Test Tubes A and B should be held in the same hand is:

avoid losing any of the solution 

The challenge with using a pipette bulb to separate layers using the technique shown in the diagram is that the _______________________ ["high vapor pressure", "density", "low vapor pressure", "high boiling point"] of the solvent may cause it to _______________________

high vapor pressure, dribble out

Match the procedural step/question to the correct answer for the NaHCO₃ (sodium bicarbonate) extraction on Tube 1 (after mixture is completely dissolved in ether).

place tube 1 on ice, add sodium bicarbonate to tube 1, wait for bubbling to subside, mix layers in tube 1 using pipette for required time, transfer bottom layer from tube 1 to tube 2

What species is in Tube 2 after transfer from this extraction?

sodium benzoate 

What species is in Tube 1 after sodium bicarbonate extraction?

4-tertbutylphenol and biphenyl

Match the procedural step/question to the correct answer for the NaOH (sodium hydroxide) extraction on mixture in Tube 1 AFTER sodium bicarbonate extraction

add naoh to tube 1, mix layers in tube 1 for required time, transfer bottom layer from tube 1 to tube 3,

What species is in Tube 3 after this extraction?

sodium 4-tertbutyl phenoxide

What species is in Tube 1 after sodium hydroxide extraction?

biphenyl

Ortho-chlorobenzoic acid has a pKa of 2.89. Para-Aminobenzoic acid has a pKa of 2.38. 4-Chlorophenol has a pKa of 9.41. You will need the following information:  The pKa of HCl is –7; pKa of carbonic acid (H₂CO₃) is 6.52 and the pKa of water is 15.

Mixture A is a mixture of Ortho-chlorobenzoic acid and 4-Chlorophenol.

Mixture B is a mixture of Ortho-chlorobenzoic acid and Para-Aminobenzoic acid.

Mixture C is a mixture of Para-Aminobenzoic acid and 4-Chlorophenol.

All mixtures are dissolved in methylene chloride

a) Why would reacting Mixture A with an aqueous solution of NaOH (sodium hydroxide) NOT separate one substance from the other?

The acidity of water is weaker than both components so sodium bicarbonate will be extracted in aqueous layer.

Ortho-chlorobenzoic acid has a pKa of 2.89. Para-Aminobenzoic acid has a pKa of 2.38. 4-Chlorophenol has a pKa of 9.41. You will need the following information:  The pKa of HCl is –7; pKa of carbonic acid (H₂CO₃) is 6.52 and the pKa of water is 15.

Mixture A is a mixture of Ortho-chlorobenzoic acid and 4-Chlorophenol.

Mixture B is a mixture of Ortho-chlorobenzoic acid and Para-Aminobenzoic acid.

Mixture C is a mixture of Para-Aminobenzoic acid and 4-Chlorophenol.

All mixtures are dissolved in methylene chloride

Why would reacting Mixture B with an aqueous solution of  NaHCO₃ (sodium bicarbonate) NOT separate one substance from the other?

the acidity of carbonic acid is weaker than both components so both will be extracted into the aqueous layer.

Ortho-chlorobenzoic acid has a pKa of 2.89. Para-Aminobenzoic acid has a pKa of 2.38. 4-Chlorophenol has a pKa of 9.41. You will need the following information:  The pKa of HCl is –7; pKa of carbonic acid (H₂CO₃) is 6.52 and the pKa of water is 15.

Mixture A is a mixture of Ortho-chlorobenzoic acid and 4-Chlorophenol.

Mixture B is a mixture of Ortho-chlorobenzoic acid and Para-Aminobenzoic acid.

Mixture C is a mixture of Para-Aminobenzoic acid and 4-Chlorophenol.

All mixtures are dissolved in methylene chloride

What species (among HCl, sodium hydroxide and sodium bicarbonate) could you use to separate the components of Mixture C?

sodium bicarbonate

Ortho-chlorobenzoic acid has a pKa of 2.89. Para-Aminobenzoic acid has a pKa of 2.38. 4-Chlorophenol has a pKa of 9.41. You will need the following information:  The pKa of HCl is –7; pKa of carbonic acid (H₂CO₃) is 6.52 and the pKa of water is 15.

Mixture A is a mixture of Ortho-chlorobenzoic acid and 4-Chlorophenol.

Mixture B is a mixture of Ortho-chlorobenzoic acid and Para-Aminobenzoic acid.

Mixture C is a mixture of Para-Aminobenzoic acid and 4-Chlorophenol.

All mixtures are dissolved in methylene chloride

What species would exist in the aqueous layer AFTER the extraction?

Sodium salt of para-aminobenzoic acid

Why did you have to carry out the extractions in the sequence you did – i.e. weak base first then strong base?

We needed to do the weak base first then the strong base because if the strong base was extracted first then we would extract both the strong and weak base. 

Why was NaCl solution added to ether layer in Tube 1?

It is added to the ether layer because it has a stronger attraction to water than organic solvents. NaCL dissolves in water and reduces the solubility of the organic compound in aqueous layer.

Why was drying agent added?

Drying agents are dded to remove traces of water in the organic layer containing organic solutes. This is because salts bonds to water molecules to form hydrated salts that can then be easily separated from the dried layer. 

What problem would arise if NaCl and drying agent (sequentially) were not added to the ether layer?

If they were not added to the ether layer than there could trace amounts of water still left in the ether layer. 

You have  a mixture of 2-chlorobenzoic acid (pKa 2.92) and 4-Bromophenol (pKa 10.2) dissolved in ether. You will need the following information:  The pKa of HCl is –7; pKa of carbonic acid (H₂CO₃) is 6.52 and the pKa of water is 15. Which species do you use to separate the mixture?

sodium bicarbonate

You have  a mixture of 2-chlorobenzoic acid (pKa 2.92) and 4-Bromophenol (pKa 10.2) dissolved in ether. You will need the following information:  The pKa of HCl is –7; pKa of carbonic acid (H₂CO₃) is 6.52 and the pKa of water is 15. Which species will remain in the ether layer?

2-Chlorobenzoic acid

Which of the options in the drop down menu should NOT be in the reaction flask when assembling the apparatus for the azeotropic distillation of n-butyl acetate that you set up? drying agent

drying agent

the apparatus should lean xx degrees and the sidearm of the distillation should be pointing xx and place a xx in the end of the side arm

10, down, cork

Which of the modifications in the drop down menu should you employ to make sure the azeotropic distillation of n-butyl acetate proceeds smoothly?

wrapping condenser with wet paper towel

In order to minimize forming a mixture of products in the reaction in the question above, which reactant would you use an excess of? why?

2,2-dimethylpropanal, It has no alpha hydrogens

did not do postlab 6 and postlab 7 and onwards, you already did prelab 7