Orgo Lab Chem 269 owl answers

A prelab outline for each experiment:

is a shortened version of the experiment handout, written in the students own words in outline or bulleted form, must be checked by and accepted by the TA before any lab work may be done, must be carefully written before coming to lab

OWL assignments constitute 15% of the final grade. Both prelab and postlab assignments are available for most experiments. Check all true statements

Extensions for OWL assignments will not be given, except in cases of extreme personal hardship, which are documented by the Dean of Students office, The Safety and Course Policy OWL assignments must be successfully completed before a student is allowed to work in the lab

Limited-Use lab hours are available to do certain things. Check all true statements.

You will be asked to leave exactly when morning hours are finished for the day, Melting points and weighings may be done as well as consulting with the TA on duty.

For make-ups,

you must carefully follow the procedure given in the handout "Make-up Policies and Procedures", you must make up the lab within one week of missing it.

To ensure that full credit may be given, the course handout, "Notebook and Grading Policies" should be read and followed carefully. Answer all statements that are true.

For work to be considered valid and acceptable, a TA signature on the pre-lab and in-lab observations is required at the end of each lab period, The required notebook is electronic and you are able to download and install MS Word.

The melting point of a sample of compound X was found to be 199 - 203 ° C. Compound X was one of four possible compounds having melting points of 199, 201, 203, and 205 ° C. Which was it most likely to be?

205

Impurities usually cause a compound to melt over a temperature range rather than at a single temperature. The 4° melting point range observed for compound X indicates that the sample contains impurities. In addition to broadening the temperature over which a compound melts, impurities also lower the temperature at which the compound melts. The melting point of a pure compound will therefore be greater than the melting point range found for an impure compound.

In this lab a melting range of ______ ° C indicates that a compound is relatively pure.

2

In a melting point determination, the heating rate as the solid is melting should be ____° C per minute.

1

If a second melting point determination must be taken for a sample, it is necessary to use a fresh sample and not the one that has already been used. Why?

The sample may have decomposed slightly

Melting points can provide the following information about a sample.

The identity, the purity

Generally speaking, the chemicals used in the organic lab are more toxic and flammable than those used in the general chemistry lab

True

Good preparation is the key to safe experimentation in the lab. Before you are allowed to work in the lab, you must present an acceptable prelab outline to your TA. This will count as ___points of your non-formal lab report grade.

5

Permanent injury to the eyes can happen quickly and without warning. An accident or carelessness caused by you or a neighbor can result in the loss of your or someone else's eyesight. To help prevent injury to the eyes

approved eye protection will be worn at all times while you are in the lab.

Poisoning by laboratory chemicals can occur by (check all correct answers)

Inhalation, ingestation, contact with the skin.

A minor burn received by touching a hot object should be treated by

immediately immersing the burned tissue in cold water.

Which of the following is most correct? (food)

Neither food nor drink may be present in the lab, even if their containers are unopened.

Which of the following is most correct? (waste)

Chemical waste must never be placed into the sink or the trash.

Thin layer chromatography can be used to help determine (select all correct answers)

the number of components in a mixture, the purity of a compound, the identity of a compound

Give the three basic steps in TLC in the order in which they are done.

Spotting, development, visualization

A TLC analysis was run on an unknown mixture. After visualization by two methods, three spots were observed. What can be concluded?

There are at least three components in the mixture.

In a TLC analysis if the Rf's of the spots are too small,

a development solvent of higher polarity should be used.

In a TLC analysis, if the solvent was observed to travel 10.0 cm and the spot was observed to travel 5.10 cm, what is the Rf for that spot?

0.51

A solid sample melted at 177.0-181.0°C. The compound was one of four possibilities, having the mp's shown below. Which was it most likely to be?

181.0

179.0

183.5

177.0

183.5

The three general types of impurities that may contaminate a solid sample are

insoluble impurities, soluble impurities, colored impurities.

Two obvious structural features that may affect the solubility of a compound are

its ability to form hydrogen bonds, its polarity

The following compound would be expected to be most soluble in which of the following solvents (choose one): alchol

Hexane

The correct amount of solvent to use in a crystallization is

the minimum needed to dissolve the solid near the boiling point of the solution

After removing the crystallization solvent from the crystals, the crystals are rinsed with fresh solvent to remove impurities clinging to the surface of the crystals. Which statement is most correct?

The crystals should be rinsed with a minimum amount of ice-cold solvent.

Which of the following would be considered to be physical properties? (check all correct answers)

Solubility, boiling point, melting point

What structural characteristic of thalidomide accounts for the fact that in one form it acts as a sedative and in another it acts as a teratogen?

Chirality

Which of the following would be considered to be chemical properties? (check all correct answers)

Acidity and rate of reactions

In a TLC analysis, if the Rf of a compound was found to be too large, a ______ (spotting or development?) solvent having a _________ (lower or higher?) polarity should be chosen

Development, lower

After development and visualization of a TLC plate, five spots were observed. What can be concluded about the number of components in the original mixture?

There are at least five components in the mixture.

Decaffeinating coffee or tea represents the following type of extraction:

solution into another solvent

When two liquids that are mostly insoluble in one another are mixed together, they separate out into two layers. Whether one liquid is the upper or lower layer depends upon the

the relative densities of the two liquids

A sample of naphthalene was mixed with water and tert-butyl methyl ether.

The naphthalene dissolved mostly in the (water or ether?) ________ layer.

The ether layer was the (upper or lower?) ________layer.

ether, upper

A sample of glucose is added to a mixture of water and tert-butyl methyl ether.

The glucose will dissolve mostly in the (ether or water?) ____________layer.

The water layer will be the (upper or lower?)

____________layer?

Water, lower

Which of the following organic solvents would be suitable for use in the extraction of an aqueous solution?

Hexane

A mixture of benzoic acid and naphthalene was dissolved in tert-butyl methyl ether and the resulting solution was extracted with aqueous sodium bicarbonate. The major organic species (excluding solvent) that is present in the lower layer is

Benzoic ion and sodium ion

A mixture of benzoic acid and naphthalene was dissolved in tert-butyl methyl ether and the resulting solution was extracted with aqueous sodium bicarbonate. The major organic species (excluding solvent) that is present in the upper layer is

Two benzene rings attached

A mixture of benzoic acid and naphthalene was dissolved in tert-butyl methyl ether and the resulting solution was extracted with aqueous sodium bicarbonate. The lower layer was separated and to it was added concentrated hydrochloric acid, upon which a white precipitate formed. What was the structure of the precipitate?

Benzoic acid

The solubility of substance A in four different solvents at low temperature and high temperature are given below. Which solvent is the best for recrystallizing substance A ?

Pick the one with the highest high T solubility and lowest low T solubility. Water

In a micro scale distillation, the rate of distillation should be about one drop per ________to _________seconds.

20 to 30

In a distillation the correct position of the thermometer is

Have the beginning of the mercury aligned with the bottom of the side arm.

In a distillation what two pieces of information can be obtained? (select two)

The boiling point of each component, The ratio of the amounts of the components in the original mixture.

In this experiment a comparison of simple vs fractional distillation is done by comparing plots of _______ vs ________

Temp vs volume

A mixture of which two compounds is distilled in the first part of the experiment?

Toluene and cyclohexane

A mixture of the following compounds was dissolved in tert-butyl methyl ether and mixed thoroughly with 5% aqueous sodium bicarbonate.

The one with less hydrogen bonding ability

The graph shown is a boiling point-composition curve for a mixture of cyclohexane and toluene. The lower curve is the liquid curve and the upper curve is the vapor curve.

If a mixture consisting of 25 % cyclohexane and 75 % toluene were distilled in a fractional distillation apparatus having 2 theoretical plates, what would the composition of cyclohexane be in the first drop of distillate? ____________%

84%