chem 343

When separating a solid from a liquid via filtration, what is the name given to the liquid that is collected?

filtrate

What is the best way to remove an insoluble solid sample for recrystallization?

find a solvent to dissolve the desired compound and then do hot gravity filtration

In which waste container should the liquid solvent, acetone (C3H6O) be disposed?

non-halogenated waste container

Which of the following demonstrates the proper use of a sep funnel during washings and/or extractions?

All of these **look up proper sep funnel use

When you collect your crystals at the end of lab, why do you wash with cold solvent (as opposed to room temp or hot solvent)?

So you don't redissolve the crystals back into the liquid.

Which of the following situations would contribute to a lower yield of product?

a and c would both contribute to a lower yield

Which of the following should be done before, during, and/or after an extraction?

-->Check that the sep funnel is properly assembled; rubber O ring between the teflon washer and teflon nut on the stopcock to avoid leaks

When using Siwoloboff's method, when is the thermometer read to determine the boiling point of the unknown liquid?

-->as soon as the unknown liquid enters the capillary, read the thermometer to obtain the first value of the boiling rang. -->When the unknown liquid fills the tube, read the thermometer again to obtain the second range

What does it mean if a mixed solvent system such as ethanol/water is suggested for a recrystallization?

-ethanol has good dissolving abilities for many organics, but is also miscible with water. -Water can reduce the solubility of many organics and thus induce crystallization

What is a sign that a solid sample may contain an impurity?

a higher/broader melting point range

Which of the following combinations of solvents would be good for an extraction?

need nonpolar and water; diethyl ether and water or methanol and water

What is the rf value for a spot that traveled 2.0 cm up a TLC plate if the solvent front traveled to 8.0 cm?

0.25 2.0/8.0 = 2.5

The following reaction is done in a chem-343 lab: Sodium ethoxide + 1-bromobutane --> 1-ethoxybutane What is the electrophile in the above reaction?

1-bromobutane

What is the electrophile in the reaction? (sodium ethoxide + 1-bromobutane --> 1 ethoxybutane + NaBr)

1-bromobutane

Which of the following statements is/are not true about a distillation set-up? 1. The water hoses must be securely attached to the condenser and faucet 2. The water will enter from the top of the condenser and exit from the bottom of the condenser and exit from the bottom of the condenser so that it flows "downward" 3. The water serves to cool the vapors causing them to condense 4. The lowest boiling liquid will be collected first.

2. The water will enter from the top of the condenser and exit from the bottom of the condenser and exit from the bottom of the condenser so that it flows downward

The following reaction is done in a chem-343 lab: Sodium ethoxide + 1-bromobutane --> 1-ethoxybutane If 10.0 mL of 21% by weight sodium ethoxide solution is used, how many mmol of sodium ethoxide are reacted?

26.7 mmol

What is an azeotrope?

A mixture of two or more liquids in such a ratio that it's composition cannot be changed by vaporizing it.

If you have dissolved colored impurity (and some solid contaminants) when you dissolve your unknown in the appropriate solvent, what should be done?

Activated charcoal removes colored impurities

If the compound shown in the table below were separated by column chromatography with ether on silica gel, which would elute first? Rf Factors: 1. 0.10 2. 0.26 3. 0.23 4. 0.40

B. 1-napthalene (0.40)

Reactions rates are affected by the type of solvent that is used. Which of the following is not a polar protic solvent? 1. CH3OH 2. CH3CN 3. CH3COOH 4. H2O

CH3CN

In last week's experiment, the hexane solution from the spinach extraction contained a number of different plant pigments (and possibly other organic substances). To observe the components in the hexane solution, a sample of the solution was subjected to TLC. Which of the following best describes the TLC experiment?

Hexane was the mobile phase and the mobile phase was nonpolar

In today's experiment, butan-2-ol is dehydrated to yield 3 isometric butenes. How will the mixture of butene products be analyzed to see how much of each one was formed?

IR spectroscopy

Why is filter paper fluted for gravity filtration?

It allows more surface area of the paper to come in to contact with the mixture being filtered

A melting point for a known substance was high and broad. Why might that be?

It may contain an impurity

A dehydration reaction was done starting with 2.00 g of butan-2-ol. The data collected after the reaction is shown below. GC integration: 1. 65.43 2. 46.02 3. 13.25 total mass: 1.3 g Molar mass: 84.12 How many grams of each alkene were produced?

Math

The following reaction is done in a chem-343 lab: Sodium ethoxide + 1-bromobutane --> 1-ethoxybutane What is the reaction mechanism for the above reaction?

SN2

A student reported the following amounts of her compound recovered with each of 3 successive extractions using the same volume of solvent each time: 0.45g, 0.23g, 0.30g. Based on your understanding of the partition coefficient, why can't this be correct?

She should have obtained smaller amounts of compound with each successive extraction

You have a mixture of three compounds shown below. Which compound would distill first and which compound would distill last? (quiz 5)

The compound with the lower boiling point --> longer chain, high boiling point --> alcohols increase boiling point as well

When using a mixed solvent system such as water and methanol to do a re-crystallization, which of the following is true?

The first step in the recrystallization process is to dissolve the compound in a minimum of one of the hot solvents

The following reaction is done in a chem-343 lab: Sodium ethoxide + 1-bromobutane --> 1-ethoxybutane A precipitate is formed during the reaction. What is likely the precipitate and how is it completely removed from the reaction mixture?

The precipitation is sodium bromide and it dissolves in the aqueous layer during quenching and is removed during the extraction work-up

During gravity filtration, a student forgets to heat the solution before running it through a filter. After capturing the filtrate, the student analyzes the sample by spectroscopy and finds none of the desired product in the filtrate. What likely occurred to the student's product?

The product precipitated and is present in the residue

During gravity filtration, a student forgets to heat the solution before running it through the filter. After capturing the filtrate, the student analyzes the sample by spectroscopy and finds none of the desired product in the filtrate. What likely occurred to the student's product?

The product precipitated and is present in the residue

The following reaction is done in a chem-343 lab: Sodium ethoxide + 1-bromobutane --> 1-ethoxybutane The reaction of 1-bromobutane with sodium ethoxide affords the product 1-ethoxybutane. What is the effect of doubling the concentration of both sodium ethoxide and 1-bromobutane on the rate of the reaction?

The rate increases by a factor of 4

If you did all of the reading, then you know about the partition coefficient of a compound and how that affects the completeness of each extraction. Without doing calculations, what is the big take home message that the calculations show you for each successive extraction?

Using multiple smaller volume extractions extracts a greater mass of the compound than does one larger volume

The hexane solution from the spinach extraction contained a number of different plant pigments (and possibly other organic substances). To observe the components in the hexane solution, a sample of the solution was subjected to TLC. Which of the following statements is true?

a less polar component had a larger Rf value than a more polar component

What is a forerun?

a low boiling liquid that distills over long before the boiling point of the liquid you want has started to boil

Which of the following statements are true about the reactants and products shown below? (quiz 4)

a reaction will not occur

Which of the following statements are true about the reactants and products shown below?

a reaction will not occur **why/why not will the reaction occur

When is it appropriate to use a short path distillation set-up and how does a short path distillation differ from a simple distillation set-up?

a short path distillation can be done when the liquids have very differing boiling points and it differs in that there is no condenser used in a short path distillation

An agent used for decolorization is? (lab 3, quiz 2)

activated charcoal

If 0.67g of pure solid is collected from 0.85g of crude solid, what is the percent recovery?

actual/theoretical X 100

When preparing a gravity chromatography column, which of the following practices should be followed?

all of the above *find practices

When conducting a "safe" distillation in this lab, which of the following should always be done? 1. A boiling chip should be placed in the distillation flask 2. The glassware joints should be lightly greased 3. All openings should be sealed including the attachment of the receiving flask to the apparatus, to ensure an air-proof, water-proof system

all should be done

Like the experiments last week, today you will perform a liquid-liquid extraction. The organic solvent you will use is hexane (hexanes to be specific). After the hexane layer is separated, you will treat it with anhydrous sodium sulfate. What is the purpose of this step?

as a drying agent to remove any remaining water in the solution

After crystals are collected, they should be washed with? (Lab 3 quiz 2)

cold solvent

Distillate is a liquid that _____.

condenses after distillation

Why are deuterated solvents used in NMR spectroscopy?

deuterated solvents do not contain protons so they do not give an NMR signal that could interfere with your compounds NMR signals

the following reaction (sodium ethoxide + 1-bromobutane --> 1 ethoxybutane + NaBr). Ethanol was used as the solvent and diethyl ether was used in the extraction work-up. If everything worked as it was supposed to, what will be distilled today? What compound will be collected as the first distillate?

diethyl ether and 1-ethoxybutane will be distilled. Diethyl ether will be the first distillate

Which of the following combinations of solvents would be good for extraction?

diethyl ether and water --> nonpolar and water

What is a sign that a solid sample may contain an impurity?

different colors, broad melting point range and a value that is lower than than the literature value

How could a water-soluble, organic base be separated from a water-insoluble, neutral organic compound?

dissolve both compounds in ether and extract it with an acid

For the Williamson-Ether synthesis, 25 mL of 21% by weight sodium ethoxide is used. The density of the solution is 0.868 g/mL and the mm of sodium ethoxide is 68.05 g/mol. How many mmols of sodium ethoxide were used?

do the math

In today's experiment, butan-2-ol is dehydrated to yield 3 isometric butenes. If 60 mmol of butan-2-ol is used and the product mixture contains 10.0 mmol of butene #1, 30.0 mmol of butene #2, and 20.0 mmol of butene #3, what is the mol fraction of each in the product mixture?

do the math

What does it mean if a mixed solvent system such as ethanol/water is suggested for a recrystallization?

ethanol is used for dissolving organics, while water reduces the solubility of many organics and induces crystallization

Fractional distillation under atmospheric pressure would be most likely to be used to separate which of the following compounds?

ethyl acetate (boiling point of 77 oC) and ethanol (boiling point of 80 oC)

Once you have collected your distillate, you next need to separate your cinnemaldehyde or eugenol from the water. How will you do this?

extract the product into the DCM

You have performed several separation techniques and will learn new ones such as chromatography this week. Based on your experience in previous labs, and the readings for this week, how could the compounds shown below be best separated? (lab 6 or 7)

first step, do an extraction by dissolving both compounds in ether and washing the ether with a base such as sodium bicarbonate solution

In fractional distillation, a large surface area for condensation is provided through?

fractionating column

In which container should dichloromethane (DCM) be disposed?

halogenated waste container

Often saturated sodium bicarbonate solution is used to do a wash during the extraction process. What is a saturated sodium bicarbonate solution?

it is NaHCO3 dissolved in water to a point that no more of it can dissolve in the water

During the workup of the reaction, diethyl ether is washed with the brine solution. What is the purpose of this wash?

it is to "predry" the diethyl ether; removes traces of water in the ether

Solvents in crystallization should be? (lab 3 quiz 2)

miscible

When you set up for microscale boiling point determination, you are asked to put a capillary tube into the test tube containing your unknown liquid. How should the capillary tube be inserted?

open end down in the liquid

Think of your experiment from last week and choose which of the following is true about extracting an organic compound into a given solvent.

organic substance with acidic functional groups may dissolve in water if treated with base

You will use two different kinds (thin layer and column) chromatography as a means of separation. Both of the chromatographic experiments that you will perform will separate the components of a mixture based on which physical property?

polarity/solubility

Which of the following is not a step in the process of distillation?

precipitation

Which of the factors below are not considered when interpreting a proton NMR spectrum?

retention time

When you set up for microscale boiling point determination, you are asked to rubber band a thermometer to the test tube containing the unknown liquid. Where should you position the bulb of the thermometer?

slightly below the opening of the 3-way adapter leading to the condenser

When you collect your crystals at the end of lab, why do you wash with cold solvent, as opposed to room temp solvent?

so that they don't dissolve into the filtrate

The following reaction is done in a chem-343 lab: Sodium ethoxide + 1-bromobutane --> 1-ethoxybutane What is the nucleophile in the above reaction?

sodium ethoxide

For crystallization, the solution should be? Lab 3/quiz 2

solution should be miscible

Why do organic chemists often rinse glassware with an organic solvent, like acetone or alcohol, after washing with soap and water?

sometimes the compounds are not highly soluible in water, so using an organic solvent will rinse out any remaining nonpolar/slightly polar residues

A microscale boiling point determination has been correctly set up and is heating. At the start, a small stream of air bubbles exits from the capillary tube. Then the rate of bubbling becomes faster, what is causing the bubbling?

the bubbles are actually the vapor of the unknown liquid being forced out of the tube

Dichloromethane (DCM) is used as a re-crystallization solvent. The solid is collected by vacuum filtration. Where should the filtrate be disposed?

the halogenated waste container

Sodium ethoxide + 1-bromobutane --> 1-ethoxybutane The reaction of 1-bromobutane with sodium ethoxide affords the product 1-ethoxybutane . What is the effect of doubling the concentration of sodium ethoxide on the rate of reaction?

the rate increases by a factor of 2

Which of the following would be the best procedure for extracting acetaldehyde from an aqueous solution?

three successive extractions with 33.3 mL portions of ether

What is the point of using a boiling stone or stir stick when heating a liquid?

to provide a surface on which gas bubbles can form in the liquid to avoid superheating

The first step of today's experiment is to grind spinach leaves in acetone with a mortar and pestle. The purpose of this step is to:

to solubilize the organic plant pigments in the spinach leaves

Like the experiments last week, today you will perform a liquid-liquid extraction. The organic solvent you will use is hexane (hexanes to be specific). After the hexane layer is separated, you will treat it with anhydrous sodium sulfate. How can you tell when you have added enough?

when it starts to clump up in the container

When should you record the first boiling point range during a distillation?

when the vapor condenses to form a drop of liquid on the bulb of the thermometer and the temperature stabilizes