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A-level Chemistry > Module 6: Chromatography and Spectroscopy V1 > Flashcards

Module 6: Chromatography and Spectroscopy V1 Flashcards

1
Q

Why should a TLC plate only be handled by the edges?

A

To avoid contamination. ✓

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2
Q

Why is a base-line drawn in pencil?

A

To avoid ink from dissolving and contaminating the TLC plate ✓

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3
Q

How is solution added to the base line?

A

A capillary tube to spot a small amount of solution on the base line ✓

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4
Q

What is done to ensure the solvent rises up the TLC plate

A

Watch glass is placed over the beaker ✓

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5
Q

When is the TLC plate removed

A

When the solvent is approximately 1 cm from the top of the plate ✓

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6
Q

After the TLC plate has dried, what must be done to locate the spots

A

Circle any visible spots ✓

or use a locating agent e.g. ninhydrin ✓

or a UV lamp to visualise the spots that cannot be seen. ✓

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7
Q

How can Rf values be used in a rates experiments

A

Take a sample at regular intervals and run a TLC along with the reactants. ✓

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8
Q

How can Rf values be used to predict the identity of a compound

A

Identify components by matching Rf value to known values in a database. ✓

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9
Q

Give two limitations to TLC

A

Similar compounds have similar Rf values so spots may overlap or not fully separate. ✓

New compounds will not have database values to compare with. ✓

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10
Q

Explain what a spot higher up with a larger Rf value shows

A

A spot higher up with a larger Rf value is more soluble in and forms stronger intermolecular forces with the mobile phase. ✓

Less polar compound ✓

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11
Q

Explain what a spot lower down with a smaller Rf value shows

A

A spot lower down with a smaller Rf value is less soluble in the mobile phase and forms stronger intermolecular forces with the stationary phase. ✓

More polar compound. ✓

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12
Q

What does increasing the polarity of the solvent do?

A

Increasing the polarity of the solvent means the polar compound will be more soluble in the mobile phase ✓

and the Rf value would be greater ✓

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13
Q

What is the process by which compounds are separated in TLC?

A

Separation by adsorption ✓

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14
Q

What is the stationary and mobile phase in TLC

A

Solid stationary phase of silica, SiO2, which is polar ✓

Mobile phase is a liquid solvent ✓

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15
Q

Once the spots are visualised, how do you analyse the TLC?

A

Measure how far each spot travels and calculate the Rf value. ✓

Compare the Rf values to database values. ✓

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16
Q

What is the process by which compounds are separated in GC?

A

Relative solubility in the stationary phase. ✓

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17
Q

What is the mobile phase in GC?

A

Inert gas such as N2. ✓

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18
Q

Define “retention time” in GC?

A

Time taken from injection to detection. ✓

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19
Q

Name the process by which TLC separates amino acids

A

Adsorption ✓

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20
Q

Explain how the student could analyse the chromatogram to identify the three α-amino acids present

A

Measure how far each spot travels and calculate the Rf value. ✓

Compare Rf values to database values. ✓

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21
Q

Several α-amino acids have structures that are very similar. Suggest why this could cause problems when using TLC to analyse mixtures of α-amino acids

A

Similar compounds have similar Rf values ✓

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22
Q

State two limitations of GC

A

Some compounds have similar retention times ✓

New compounds will not have database values to compare with ✓

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23
Q

State the observation for the reaction between the following. Include an equation in your answer:

But-1-ene and bromine

A
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24
Q

State the observation for the reaction between the following. Include an equation in your answer:

Ethanoic acid and potassium carbonate

A
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25
Q

State the observation for the reaction between the following. Include an equation in your answer:

Propanal and Tollens’ reagent.

A
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26
Q

State the observation for the reaction between the following. Include an equation in your answer:

2,3-dimethylpentan-1-ol and acidified potassium dichromate under reflux

A
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27
Q

State the observation for the reaction between the following. Include an equation in your answer:

2-hydroxybenzoic acid and sodium

A
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28
Q

State the observation for the reaction between the following. Include an equation in your answer:

3-hydroxyphenylethanol and NaOH

A
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29
Q

State the observation for the reaction between the following. Include an equation in your answer:

Phenol and sodium carbonate

A

No visible change ✓

No reaction as phenol is too weak of an acid ✓

30
Q

NaOH and 1-chlorobutane. Include the curly arrow mechanism and an ionic equation when AgNO3 is added, with state symbols and observations. Compare the rate of hydrolysis with 1-bromobutane and 1-iodobutane.

A

1-iodobutane is hydrolysed faster than 1-bromobutane which is hydrolysed faster than 1-chlorobutane. ✓

C-Cl to C-Br to C-I bonds become weaker and are broken more easily, faster rate of hydrolysis ✓

31
Q
A
32
Q

Complete the following table with observations.

A
33
Q

Give a use of NMR spectroscopy

A

MRI imaging ✓

34
Q

Describe how NMR spectroscopy works

A

Interaction of the nucleus with a strong magnetic field and low energy radio frequency ✓

35
Q

Which species can produce an NMR spectrum

A

NMR spectra with isotopes of elements that have an odd number of nucleons e.g. 1H and 13C ✓

36
Q

A student is trying to confirm the identity of a few organic compounds. Explain how a student could use Infrared spectroscopy to confirm which compound is a carboxylic acid.

A

Run IR. ✓

Peak visible in range 2500cm-1 to 3300cm-1 for O-H (Carboxylic acid) ✓

37
Q

GC-MS was used to identify the compounds present in rose oil as nerol, geraniol, citral, and menthol.

Explain how GC-MS can be used to identify these compounds.

A

GC first separates compounds based on their retention times. ✓

Mass spectrum then matched to a database to identify compounds. ✓

38
Q

GC-MS was used to identify the compounds present in rose oil as nerol, geraniol, citral, and menthol.

Suggest, with a reason, which two compounds might be present in B.

A

Neol and Geraniol. ✓

They are both primary alcohols/ stereoisomers. ✓

39
Q

Calculate the Retention factor of spot A. (yes, put your ruler against the screen)

A

Answer: 0.1-0.3. ✓

40
Q

Identify, with asterisks, all the chiral centres in menthol that cause stereoisomerism.

A
41
Q
A

Position 2: Single because no neighbouring H’s. ✓

Position 4 and 6: Triplet, because 2 neighbouring H’s. ✓

Position 5: Pentet because 4 neighbouring H’s. ✓

42
Q

Explain why Deuterated dimethylsulfoxide is used as a solvent rather than dimethylsulfoxide when conducting NMR spectroscopy.

A

Deuterated dimethylsulfoxide does not contain H’s and does not give a single peak. ✓

43
Q

Explain why TMS is added when conducting NMR spectroscopy

A

TMS is the standard, used as a reference with chemical shift = 0ppm. ✓

44
Q

A chemist conducts NMR spectroscopy on ethanoic acid. He runs the NMR a second time, but adds a few drops of deuterated water (D2O). What difference would you expect to see between the proton NMR spectra of ethanoic acid with and without D2O.

A

With D2O added, O-H peak disappears. ✓

45
Q

A chemist conducts NMR spectroscopy on ethylamine. He runs the NMR a second time, but adds a few drops of deuterated water (D2O). What difference would you expect to see between the proton NMR spectra of ehthylamine with and without D2O.

A

With D2O added, N-H peak disappears. ✓

46
Q

In GC, how does a liquid stationary phase separate the organic compounds in a mixture.

A

By relative solubility. ✓

47
Q

A sample contains a mixture of two esters contaminated with an alkane and an alcohol.

The chemist attempts to separate the four organic compounds in the mixture using gas
chromatography, GC.

The column in the gas chromatograph contains a liquid alkane which acts as the stationary
phase.

Suggest how well these four compounds would be separated using the alkane stationary
phase. In your answer, include some indication of the length of the retention times.
Explain your answer.

A

Alcohol would have shortest retention time
and alkane would have longest retention time. ✓

The esters would have similar retention times
because similar molecules / functional groups
have similar retention times. ✓

48
Q

Predict the number of peaks in the C13 NMR spectrum of each of these α- amino acids.

A

Penicillamine: 4. ✓

Methionine: 5. ✓

49
Q

What is the standard used in NMR spectroscopy.

A
50
Q

Predict the number of carbon environments in the C13 NMR spectrum of DDT.

A

6.

51
Q

What is the unit for chemical shift in NMR spectroscopy.

A

Chemical shift, δ, measured in ppm. ✓

52
Q

Explain why TMS is used in NMR spectroscopy.

A

Use TMS because it is non-toxic. ✓

volatile so can be easily removed at the end. ✓

It has a single intense peak of 12 H atoms and 4 carbon atoms. ✓

53
Q

What does the number of signals show you in NMR spectroscopy.

A

indicates the number of different chemical environments for 1H or 13C (but be careful with symmetry). ✓

54
Q

Identify the number of different carbon environments in 2-methylbutane

A
55
Q

Identify the number of different carbon environments in propan-1-ol

A
56
Q

Identify the number of different carbon environments in methylcyclohexane

A
57
Q

Identify the number of different carbon environments in benzene

A
58
Q
A
59
Q
A

C.

60
Q
A

D.

61
Q
A

2-Methylpropan-1-ol ✓

62
Q
A
63
Q
A
64
Q
A
65
Q
A
66
Q
A
67
Q
A
68
Q
A
69
Q
A
70
Q

State the solvent used in NMR spectroscopy.

A

CDCl3 (deuterated chloroform). ✓

71
Q

Describe how you can test for the difference between 1-bromobutane, 1-chlorobutane and 1-iodobutane.

A

Add AgNO3 in ethanol, 50 degrees celcius. ✓

AgCl white precipitate, soluble in dilute NH3 (aq) shows 1-chlorobutane being present. ✓

AgBr cream precipitate, soluble in conc. NH3 (aq) shows 1-bromobutane being present. ✓

AgI yellow precipitate, insoluble in NH3 (aq) shows 1-iodobutane being present. ✓

A-level Chemistry (15 decks)

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