Exam 1

How can you quantify the relative amount of one component in a two-component mixture based on the signals on a chromatograph?

(Area A / (Area A + Area B)) * 100

Before turning on the heat for a microscale distillation, what should you confirm about the set-up?

- presence of boiling chip - existence of some opening in the set-up - secure connections at the joints

Calculate the Rf value for a spot in a TLC experiment if the solvent moved 13.6 cm and the spot moved 9.8 cm.

0.72 R(f) = distance traveled by mixture component/distance travelled by mobile phased

Suppose a polar solvent is required for separation of a mixture in a chromatography experiment. Which solvent would be the best choice? 1. methanol, CH3OH 2. carbon tetrachloride, CCl4 3. benzene, C6H6 4. toluene, C7H8

1

All lab participants must remain prepared to use safety equipment in case of an emergency. Identify the components of effective preparation. Select one or more: 1. Being familiar with how safety equipment is used 2. Practicing with safety equipment before the start of each lab session 3. Knowing what safety equipment is available 4. Understanding where the safety equipment is located 5. Researching alternatives to the safety equipment available in lab

1, 3, 4

Identify the effect of each error during a thin layer chromatography experiment. 1. The mobile phase used does not move any of the spots at all. 2. Pen rather than pencil is used to draw the lines on the plate. 2. The TLC plate remains in the chamber even after the solvent has reached the top of the plate. 4. The solvent line is not marked after the TLC plate is removed from the chamber.

1. There can be no separation of components. 2. There will be smears on the TLC plate. 3. Accurate Rf values cannot be determined. 4. Accurate Rf values cannot be determined.

Most chemicals can be cleaned up with a general spill kit, but a few chemicals require specialized spill procedures. For each substance listed, determine whether a general spill kit is sufficient or if a specialized spill kit is needed. 1. methanol 2. acetone 3. hydrofluoric acid 4. phosphoric acid 5. mercury

1. methanol - general 2. acetone - general 3. hydrofluoric acid - special 4. phosphoric acid - general 5. mercury - special

Identify the safety equipment designed to deal with each emergency listed. 1. chemicals on clothes 2. cuts or minor burns 3. large fire on benchtop 4. fire on person 5. chemicals in eyes

1. safety shower 2. first aid kit 3. fire extinguisher 4. fire blanket 5. eyewash station

Identify the precautions to take with exits in the lab 1. Keep the exit door locked at all times. 2. Make sure lab windows are always open. 3. Do not block a door with an EXIT sign. 4. Locate the exits prior to the start of lab.

3, 4

Which task must be carried out before using a round-bottom flask at the lab bench?

A proper support, such as a cork ring, should be set in place.

What is chromatography?

A technique to separate mixtures based on the molecular properties of the involved chemicals

When working in a fume hood, what is the best position of the hood sash?

As low as possible, no more than halfway up

Where should the tip of the thermometer be placed in a microscale distillation set-up?

At or slightly below the side arm of the distillation head

In general, which characteristics are necessary for a location to be suitable for chemical storage?

cool, dry, dark

acids and bases are

corrosive

Suppose you are using distillation to separate cyclohexane and toluene. The boiling point of cyclohexane is 81 C and the boiling point of toluene is 111 C. Therefore, the liquid collected first should be ________________.

cyclohexane

After each chemical component reaches the end of the column in a gas chromatography experiment, it hits the _________.

detector

In order for a substance to be an effective mobile phase in a chromatography experiment, it must be able to move

different components of a mixture at different rates

Which types of hazards can a fume hood help protect the user against?

fires, explosions, fumes

Identify the factors that affect retention time.

flow rate of the gas phase length of column temperature of column polarity of the liquid phase polarity of the liquid phase

If you drop or break glassware in lab, first _________________________ then, ____________________________________ Finally, place all materials into the _____________________________

get thick gloves or dustpan carefully collect all the broken glassware broken glass container

In terms of apparatus, the key difference between a simple distillation setup and a fractional distillation setup is that the fractional distillation setup contains a vertical distillation column. Ideally, the temperature of this vertical column should be

higher at the bottom and lower at the top

How is a chemical sample introduced into a gas chromatograph?

It is added via syringe into an injection port.

hydroxide or bicarbonate as bases

hydroxide is a stronger base; only stronger acids will be deprotonated by the addition of a bicarbonate - acidic functional group like carboxylic acid - both - phenyl can act as a strong acid in presence of hydroxide; bicarbonate is not strong enough to remove H from phenyl - alcohols that aren't phenols -> not acidic enough to be deprotonated by either

One of the most important requirements for performing a successful fractional distillation is that there be intimate and extensive contact between the liquid (condensate) and vapor phases in the fractionating column. In the laboratory, this will be achieved by

packing the column with an inert material having a large surface area

To run a thin layer chromatography experiment with a chemical substance, begin by marking a horizontal line near the bottom of a TLC plate with __________Place a _________ spot of the substance onto the line. For the mobile phase, add a small amount of ____________at the bottom of a TLC chamber. Place the plate in, then _________ the chamber. Once the mobile phase approaches the top of the plate, remove the plate and mark the ____________line. Note the position of the spots and calculate Rf values if needed.

pencil small solvent cover solvent

Deprotonation

removal of a proton from an acid (=dehydration)

Caution must be taken when injecting a sample into the injection port, mainly due to the facts that the syringe is _________and the injection port is __________.

sharp, narrow

When using a syringe, be sure to move this tool in a _________ manner. ____________ the other people and items nearby in the lab, and always remain aware of the position of the ___________.

slow and cautious Pay attention to needle

In a gas-solid chromatography experiment, the stationary phase is a ___________ whereas is the mobile phase is a _________. The mechanism of separation is ___________.

solid gas adsorption

The substance to which the sample is bound at the start of an experiment

stationary phase

Identify the property of the sample that most corresponds to each feature of a gas chromatograph. The width of a peak in the spectrum The order of peaks in the spectrum The area under a peak in the spectrum

the absorption of the substance by the column the relative BP of the substance the amount of the substance present

An azeotrope is a mixture that has ___________ composition in the ___________. Therefore, an azeotropic mixture ___________ separated by distillation.

the same gas and liquid phases cannot (because they both boil at the dame time)

napthalene hazards

toxic; flammable; produces nauseating vapors

NFPA diamond

visual guide to hazards that apply to a substance - blue = health - red = fire - yellow = reactivity - white = special hazards -0-4 in three upper diamonds (not white) represent increasing risk - special hazards listed

Why should Bunsen burners not be used when heating organic materials?

Many organic materials are flammable and could cause a fire.

Identify the mechanism of separation via gas chromatography.

Phase distribution

What is generally the best approach when liquid from a large reagent bottle is needed in an experiment?

Pour some of the reagent from the bottle into a beaker, then use as needed in the procedure.

PASS acronym

Pull, Aim, Squeeze, Sweep

A value that quantifies the distance traveled by a substance relative to the distance traveled by the solvent

Rf

How should spill cleaning materials be discarded?

Seal in a labeled plastic bag, then place in the solid waste container.

After performing a TLC experiment, you might place the TLC plate in a container with iodine crystals. What is the purpose of the iodine crystals?

The crystals create a gas that reacts with organic compounds to help see them on the plate.

What are the concerns presented by overheating a distillation to a dry flask?

The remaining solid residue might contain explosive peroxides. The empty glassware might heat quickly, igniting vapors from the distillation.

What is the purpose of a drying agent in the work up of an organic reaction?

To absorb small amounts of water in an organic solution

Explain the separation of benzoic acid, naphthalene, and 3-nitroaniline and identify the solution used.

Both the aniline and benzoic acid are originally dissolved in the organic solvent but their acidic and basic properties can be used to separate them out. - addition of 5% HCl protonates 3-nitroaniline, extracting it into the aqueous layer. - more concentrated base, 6M NaOH, is added to remove the proton and reform aniline - additional amount of dichloromethane is used to extract the 3-nitroaniline out of the aqueous layer. - addition of 5% NaOH deprotonates benzoic acid, extracting it into the aqueous layer. - more concentrated acid, 6M HCl, is added to add back the proton and reform benzoic acid. - additional amount of dichloromethane is used to extract the benzoic acid out of the aqueous layer.

In a TLC experiment, how do you identify the components of an unknown mixture?

Compare the Rf values of the mixture components to the Rf values of pure known compounds.

What is the best listed approach for viewing spots that are not visible on a TLC plate?

Use a UV lamp.

What is the main precaution to take if a Gas Cylinder sign is present in the lab?

Visually check that the gas cylinder is restrained but keep a safe distance from i

When working in the fume hood, it is important to make an effort to minimize _________Only keep items in the hood if they are being used for _____________. Do not ________ chemicals in the fume hood unless instructed to do so.

clutter, the current experiment, store

What is the last step of any spill cleanup procedure?

Wipe down the affected area with detergent and water.

The first signal viewed on a gas chromatograph is the

air peak

Identify the types of information that can be obtained from a gas chromatography experiment. 1. qualitative 2. quantitative 3. preparative

all of the above

Aniline involves an amine, which is a ______ functional group. When an aqueous acid solution is added to an organic solution including aniline, the aniline appears in the _________ layer in its _____________form. Then, a base is added to ________ the aniline.

basic aqueous protonated reconstituted

Suppose you are going to perform a TLC experiment, which materials will you use to prepare the TLC development chamber?

beaker & filter paper

washes vs. extractions

both: techniques use a separatory funnel to separate liquid layers wash: - moves impurities into a new layer - leaves desired compound in its starting layer extraction: - involves a reaction in one of the layers; based on reactivity to solubility - leaves impurities in the starting layer - moves the desired compound from one layer to another

A method used to separate components of a mixture

chromatography

amine in an aniline...

is basic and accepts protons (amine is ammonia with an H replaced by R)

Distillation is the separation of multiple _________ based on their different __________ points. As the mixture is heated and the first component ____________, its _____________ travels through the distillation set-up and _______________ into a different container.

liquid boiling points boils vapor condenses

In a gas-liquid chromatography experiment, the stationary phase is a _________ whereas is the mobile phase is a _________. The mechanism of separation is ___________.

liquid gas partitioning

To insert a thermometer into an adapter, use _________ to prepare the thermometer. Then, hold the thermometer __________ the adapter and ___________ the thermometer into the adapter.

mineral oil, close to, slowly turn

What aspects do all chromatography experiments have in common?

mobile & stationary phase

The substance that carries the components of a mixture

mobile phase

Suppose you are performing an extraction procedure with a carboxylic acid, like a benzoic or toluic acid. Which layer should contain the carboxylic acid in a two-layer mixture of water and an organic solvent, like diethyl ether? You then add a base to form the corresponding carboxylate. Which layer should contain the carboxylate in a two-layer mixture of water and an organic solvent, like diethyl ether?

organic (neutral organic compound -> more soluble in organic solvent) aqueous (deprotonated form, negative charge -> more soluble in water)