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CHM 2210 Lab final > Lab Final > Flashcards

Lab Final Flashcards

1
Q

Which option(s) is correct about “bumping”?

A

Occurs when a liquid is heated near its boiling point and resists boiling, occurs when a liquid becomes overheated, it results in a violent eruption of vapor to release excess heat. (all)

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2
Q

The distillation process involves four general steps: heating an impure liquid to its boiling point, cooling the vapor until it solidifies, and collecting the pure compound in a flask

A

False.

The distillation process involves 3 steps: heating the impure mixture to its boiling point, condensing the vapor and collecting the condensate

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3
Q

Distillation is used for both _____ and _____

A

Purification and determination of boiling point, and separation and identification

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4
Q

I have a mixture of two unknowns, A and B. A has a boiling point of 50°C while B has a boiling point of 85°C. Which lab technique should I use to separate them?

A

Fractional distillation because the two substances do not have a boiling point difference of at least 80°C which is required for a simple distillation. Fractional distillation allows the substances to redistill successively in one step thus creating better separation.

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5
Q

How would the observed temperature be affected if distillation were performed on the top of a mountain?

A

The boiling point of a liquid is the temperature at which vapor pressure equals the atmospheric pressure. If the experiment is performed on a mountain then the pressure in the experimental environment would be lower and as a result so would the boiling point because they directly related.

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6
Q

What does the phrase “like dissolves like” refer to?

A

Polar substances dissolve polar substances while nonpolar substances dissolve nonpolar substances

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7
Q

Properties that do not change the chemical or structural nature of a substance are referred to as

A

physical properties

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8
Q

The triangular tube used to determine a substance’s melting point is called a

A

Thiele tube

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9
Q

An unknown solid is determined to have a melting point range of 84°C-89°C. This indicated that the unknown analyzed is quite pure

A

False, the range is too large for it to be very pure

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10
Q

Which solid has a lower melting point? Organic or inorganic compounds?

A

Organic compound have a significantly lower melting point than inorganic compounds

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11
Q

Can melting point be used alone to determine a substance’s identity?

A

No, many substances have the same or similar boiling point ranges

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12
Q

Recrystallization allows us to separate and purify substances by utilizing their unique physical properties, specifically:

A

their solubility and boiling point

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13
Q

Which funnel is used for vacuum filtration?

A

Buchner funnel

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14
Q

If a cooled solute does not crystallize, which technique is used to induce recrystallization?

A

scratching the inside of the beaker/flask with a glass rod to increase the surface energy of the flask or provide nucleation sites for the recrystallization to form.

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15
Q

Which chemical compound from the recrystallization experiment required a mixture of solvents (water and ethanol) to be able to recrystallize?

A

Acetylsalicylic acid or aspirin requires a mixed solvent because no single solvent will appropriately dissolve and recrystallize the compound.

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16
Q

When doing a recrystallization, what observations would prompt you to perform a hot filtration?

A

If there are insoluble impurities in the hot solution then a hot filtration is appropriate.

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17
Q

What problems might arise if a hot solution is filtered by vacuum filtration?

A

Premature recrystallization which could lead to many impurities being left in the crystal lattice of the sample as it solidifies

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18
Q

In the extraction experiment, benzoic acid was deprotonated by hydrochloric acid to become more soluble in water and later on, protonated by sodium hydroxide to become soluble in diethyl ether?

A

False benzoic acid was deprotonated by sodium hydroxide.

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19
Q

What was used in the extraction experiment to remove excess water (before placing in the hot water bath)?

A

Drying agent

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20
Q

In a separatory funnel, there are two immiscible liquids: the aqueous phase (1.02g/mL) and the organic phase (0.83g/mL) Does the aqueous layer lie on top of the organic layer?

A

No, the aqueous layer is more dense so it would lie on the bottom

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21
Q

Removing benzoic acid from a dimethoxybenzene in diethyl ether solution using sodium hydroxide is an example of

A

A liquid-liquid extraction

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22
Q

To calculate the Rf value

A

Rf=distance traveled/total distance to finish line

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23
Q

TLC stands for

A

Thin Layer Chromatography

24
Q

In a TLC experiment, the silica plate is the more ______ phase. The 2:1 hexane/ether eluent is the more ____ phase

A

polar; nonpolar

25
Q

TLC involves two phases, one _____ phase and one _____ phase.

A

stationary; mobile

26
Q

In TLC, the solvent moves up the place by capillary action. In column chromatography. the solvent flows through the column because of _____

A

gravity

27
Q

Which solute is the least polar? Acetylferrocene, hexane, TBME, Ferrocene, Acetone

A

Ferrocene

Hexane is the least polar SOLVENT

28
Q

In column chromatography, the solvents are switched throughout the experiment in the order of most polar to least polar (Hexane ->Hexane & TBME->TBME->Acetone to be able to separate the mixture of ferrocene and acetylferrocene

A

False, the solvents are added in order of increasing polarity. Hexane being the least polar, goes first

29
Q

Name the stationary phase used in column chromatography

A

Alumina

30
Q

Which of these variable does not affect the separation of your sample in Gas chromatography?

A

The polarity of the mobile phase

Things that do affect the separation: vapor pressure, temperature of the column, column size,

31
Q

What is the Leaving Group for the reaction that occured in the Dehydration experiment?

A

H2O

32
Q

Phosphoric acid (H3PO4) used in the dehydration experiment should be taken into consideration for the percent yield calculation

A

False it is not in the final products because the alkenes are washed with aqueous sodium bicarbonate to remove any excess phosphoric acid. This is why the acidity of the solution is tested with pH paper.

33
Q

The Dehydration experiment that was done last week involved the dehydration of a cycloalkane to form two cycloalkenes

A

True

obtaining 1-methylcyclohexene and 3-methylcyclohexene from 2-methylcyclohexanol

34
Q

What is a nucleophile?

A

A chemical species that donates an electron pair to form a bond

35
Q

The formation of a carbocation during an SN1 reaction is the rate-determining (slowest) step.

A

The breaking of the carbon-halogen bond of t-butyl chloride to form a reactive intermediate, a carbocation, and a chloride ion.

36
Q

What type of nucleophilic substitution reaction does t-amyl alcohol go through to form a t-amyl chloride?

A

SN1

37
Q

Based on the Grignard Reaction lab, the Biphenyl product that is formed is the result of a heat-catalyzed coupling reaction of the Grignard reagent with bromobenzene

A

True

38
Q

The Grignard reagent reacts easily with

A

Oxygen, Water, Carbon Dioxide and many other substances that is why it must be used as soon as it is formed. Highly reactive

39
Q

The slowest step in a chemical reaction is known as the rate-determining step

A

True

40
Q

This experiment will examine the temperature of a chemical reaction using Bromophenol blue as an indicator

A

False, bromophenol blue is a pH indicator

41
Q

Solvolysis means a reaction in which the solvent is the ____

A

nucleophile

42
Q

In the distillation apparatus water enters near the bottom part of condenser and exits near the round bottom flask because

A

it cools the vapor

43
Q

Why would ethyl alcohol not be a good solvent to use with water in an extraction?

A

Ethyl alcohol is soluble in water, the miscibility of the two liquids would not allow for separation and layers to form.

44
Q

When the organic layer is less dense than the aqueous layer

A

it is important to pour the organic layer from the top of the funnel after drawing off the aqueous layer to prevent any excess water from getting into the organic layer

45
Q

Describe a procedure that might be used to separate p-dichlorobenzene (a neutral compound) from p-chloroaniline (a basic compound) by extraction.

A

Create a solution by mixing the sample containing p-dichlorobenzene and p-chloroaniline with a mixture of ether and water. Place the solution into the separatory funnel and add HCl. The p-chloroaniline with interact with the HCl and form the aqueous layer while the p-dichlorobenzene will form the organic layer. Once the phases are separated, add NaOH to the aqueous layer to isolate the p-chloroaniline. Evaporate both samples to isolate the solutes

46
Q

Why is it necessary to remove the stopper from the separatory funnel when the liquid is being drained from it through the stopcock?

A

To prevent a vacuum from forming.

47
Q

What does HCl do in the extraction experiment?

A

Protonates the benzoate anion

48
Q

How does a interact with a typical stationary phase?

A

If the molecule is also polar, the solute interacts with the OH- groups of the stationary phase (dipole-dipole interactions/ attractive forces)

49
Q

The mobile phase in gas chromatography is often

A

He or N2

50
Q

The compound that comes out first in gas chromatography is

A

The more volatile compound.

And the peak height is relative to the amount of sample used.

51
Q

Dehydration involves:

A

fractional distillation, extraction, and gas chromatography

52
Q

Describe the dehydration experiment

A

fractional distillation of 2-methylcyclohexanol using phosphoric acid to protonate the hydroxyl group and weaken the base is done. The weakened base creates a better leaving group in the form of water (good leaving group because it is stable on its own), then the alkenes separate as distillates because they have lower boiling points, these products are then extracted using sodium hydroxide and water (the alkenes will be in the upper organic layer). Then a gas chromatogram is obtained to determine the composition of each alkene.

53
Q

Grignard reagents react with ___ to produce ___

A

1: carbonyl groups in aldehydes; secondary alcohols
2: carbonyl in ketones and esters; tertiary alcohols
3: carbon on CO2; carboxylic acid

54
Q

Grignard reagent acts as a

A

nucleophile (that seeks electrophilic carbon that is in the carbonyl functional group)

It can also react with water to form a longer alkyl chain.

55
Q

What are the two products of the grignard experiment

A

Biphenyl and benzoic acid.

Biphenyl is produced from the bromobenzene if the reaction is too hot.

CHM 2210 Lab final (1 decks)

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