CHEM 225 Prelab and Postlab Quizzes

A mixture consisting of 50 mL of cylohexene and 50 mL of xylene is boiling in a round bottom flask. The vapors above the boiling liquid are

enriched in cyclohexene

Which type of spectroscopy reveals the specific placement and connectivity of atoms?

NMR Spectroscopy

Where was the acidic component of the mixture at the end of your extraction?

Precipitated with HCl and vacuum filtered.

The major safety hazard with the Beilstein test is what?

using the Bunsen burner with the highly flammable test compounds

What types of intermolecular interactions are present in alkanes? (Select all that apply)

van der Waals

What types of intermolecular interactions are present in alcohols? (Select all that apply)

van der Waals , hydrogen bonding , dipole-dipole

The boiling point of a liquid is defined as the temperature at which the ____ of the liquid equals atmospheric pressure. (there are two words in the answer)

vapor pressure

Distillation is the process of____ a liquid, ____ the vapor, and ____ the condensate in another container.

vaporizing , condensing , collecting

How many signals would one observe in the broadband-decoupled carbon-13 NMR spectrum of ethane?

1

Because the boiling point is sensitive to pressure, it is important to record the barometric pressure when determining a boiling point if the determination is being conducted at an elevation significantly above or below sea level. Water boils at ____ °C at sea level, but in Denver (5,000 ft) it boils at ___ °C while on Mt. Everest (29,029 ft), boiling water only reaches ___ °C.

100 , 93 , 72

Which nuclei are most useful for organic structure determination using NMR spectroscopy? (Select all that apply.)

1H , 13C

How many signals would one observe in the broadband-decoupled carbon-13 NMR of ethanol?

2

Which size round bottom flask would be the best to use to perform a simple distillation on 20 mL of liquid?

50 mL

What is the name of the instrument that will be used in the lab to measure refractive index? (Spelling counts.)

Abbe Refractometer

Which of the following are we NOT performing a chemical test to confirm? (Functional Group)

Alcohol

The impure benzoic acid sample we will use in lab contains which of the following components?

Benzoic Acid Sodium Acetate

Where was the neutral component of the mixture at the end of your extraction?

Crystallized on the watch glass as solvent evaporated.

Because the boiling points are within 40 °C of each other, it is possible to use simple distillation to completely purify the hexane from the toluene from the 50/50 mixture.

False

If you mix compound A (melting point range: 43-44 °C) with compound B (melting point range: 44-45 °C), then you will observe the mixture to have a melting point range of 43-45 °C.

False

If you take too much of a starting material, it is okay to put the excess back into the container from which it came.

False

In the lab, melting points are measured as single temperature values.

False

Look at the differences between your temperature measurement for the boiling point of alcohol vs. the literature boiling point and your temperature measurement for the ice water bath vs. the literature value. With that in mind, answer True or False to the following statement: As the temperature you're measuring increases, the difference between the measured temperature and the literature temperature generally decreases. (In other words, these thermometers are generally more accurate at higher temperatures.)

False

Non-mercury thermometers are just as accurate as mercury thermometers.

False

The four chemical tests must be done in a specific order in order to work properly.

False

When distilling a 50/50 mixture of hexane and toluene, which of the two components in the mixture will you distill off first?

Hexane

What type of spectroscopy contains signals that are characteristic of specific functional groups?

Infrared Spectroscopy

In this lab, you will be using a ____ apparatus to measure melting point ranges.

Mel-Temp

The boiling points in this experiment will be measured using a ______ setup.

Simple Distillation

What physical property of organic compounds does recrystallization exploit to achieve purification?

Solubility

The refractive index for a given compound depends on what?

Temperature Wavelength

What piece of glassware will you use for the bromination test?

Test Tube

Why is benzoic acid more soluble in a basic aqueous solution than it is in neutral water?

The base deprotonates the carboxylic acid, and the anion form is more soluble than the neutral form.

Which of the following compounds would produce a 13C NMR signal furthest downfield? Downfield = larger chemical shift.

Trichloromethane

Impurities should be more soluble in the solvent than the desired material.

True

The boiling point of a liquid is dependent on pressure.

True

What is the step we will use to physically separate and collect the recrystallized benzoic acid?

Vacuum Filtration

The temperature of a pure boiling liquid is equal to the temperature of the ______ above the liquid.

Vapors

When performing liquid-liquid extractions, the bottom layer should be removed through the ____ , and the top layer should be removed through the ____ .

bottom , top

To perform a melting point determination, a small amount of powdered sample is placed inside a melting point ___ tube.

capillary

Measuring the boiling point of a compound can be used to ________ (Select all that apply)

confirm the compound's identity assess the compound's purity

Branching in the hydrocarbon chain of an alcohol ____ the boiling point compared to an alcohol with a linear hydrocarbon portion.

decreases

Impure samples have melting point ranges that are both ____ and ____ compared to a pure sample.

depressed , broadened

The normal boiling point of a compound is measured at standard pressure, which is equal to 760 ___ or 1 ___ . (Use the standard abbreviations in your answers.)

mmHg , atm

The phenomenon of melting point depression is used in every-day life during the winter whenever roads are salted. Ice and salt are mixed together to lower the melting point of water, making roads less slippery until colder temperatures. The precise composition of salt and ice to yield the lowest melting point temperature is with 23 wt% salt. This value is called the ____ point for a mixture. (Be sure to spell your answer correctly.)

eutectic

When organic molecules absorb radiant energy in the IR region, specific bonds within the molecule become

excited and vibrate

An extraction ____ is a convenient way to display each of the steps of a reactive (or acid-base) extraction.

flow chart

A primary alcohol will have a ____ boiling point than a secondary alcohol with the same number of carbon atoms.

higher

The faster one performs a melting point determination, the _____ the melting point range will be.

less accurate

Crushing a solid compound into a fine powder results in a _____ melting point range than melting one large crystal.

more accurate

Organic acids and bases in their ____ form are soluble in organic solvents, but the corresponding ___ are more water-soluble. Therefore, converting acids and bases to the corresponding ____ provides a convenient tool to separate acidic, alkaline and neutral organic compounds.

neutral , salts , salt

While directly measuring a melting point in the lab, you should use a setting on the apparatus so that the temperature rises ___ than __ to __ degrees per minute. (Enter a numerical value for each of the blanks.)

no more , 2 , 3

The ratio of concentrations of a solute in each layer is defined by the ____ K. (there are two words in the answer; spelling counts.)

partition coefficient

In terms of lab safety and lab rules, being aware of and taking precautions against potential hazards is the best way to

prevent accidents before they happen

Because the presence of impurities lowers the melting point, the melting point can be a good indicator of purity: the____ the material, the ___ its melting point, and the ___ the melting point range.

purer , higher , narrower

Melting points are always measured as a ____ .

range

A(n) ____ extraction involves changing the polarity (and therefore solubility) of a compound using acid/base chemistry.

reactive

What piece of glassware is used to perform liquid-liquid extractions? (Spelling counts.)

separatory funnel

In liquid-liquid extraction, separation of the compound of interest is based on its

solubility

Crystals grow from ____ solutions.

supersaturated