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Chemistry OCR A-Level > Chapter 29 > Flashcards

Chapter 29 Flashcards

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1
Q

What is chromatography used for?

A

to separate individual components from a mixture of substances

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2
Q

What do all forms of chromatography have?

A

1) stationary phase

2) mobile phase

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3
Q

What state is the stationary phase?

A

solid/liquid supported on a solid

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4
Q

What state is the mobile phase?

A

liquid/gas

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5
Q

What is chromatography used for?

A

1) analysis of: drugs/plastics/flavouring/air samples/air samples
2) applications in forensic science

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6
Q

What is a TLC plate?

A

plastic sheet/glass coated with a thin layer of a solid adsorbent substance - usually silica

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7
Q

In TLC, what phase is the adsorbent?

A

stationary phase

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8
Q

What is adsorption?

A

the process by which the solid silica holds different substances in the mixture to its surface

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9
Q

How do you carry out TLC?

A

1) draw a pencil line 1cm from the end of a TLC plate
2) use a capillary tube to spot a small amount of the sample solution on the base line
3) prepare a chromatography tank from a small beaker with a watch glass on top. pour solvent into the beaker to a depth of 0.5cm
4) place the TLC plate in the beaker, making sure the solvent does not cover the spot, and cover with the watch glass
5) allow the solvent to rise until it is 1cm below the top of the plate. remove the plate and mark the solvent front in pencil
6) circle any visible spots/hold a UV lamp over the plate to locate spots/spray with a locating agent (iodine) to locate spots

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10
Q

How are thin layer chromatograms analysed?

A

by calculating the value for the retention factor, Rf

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11
Q

Rf =

A

distance moved by the component / distance moved by the solvent front

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12
Q

Why would you run a TLC alongside pure samples of compounds that may be present?

A

it is easier to identify the amino acids in the unknown sample visually, without needing to calculate any Rf values

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13
Q

What is gas chromatography used for?

A

separating + identifying volatile organic compounds present in a mixture

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14
Q

What is the stationary phase in gas chromatography?

A

a high boiling liquid adsorbed onto an inert solid support

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15
Q

What is the mobile phase in gas chromatography?

A

an inert carrier gas (helium/neon)

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16
Q

How do you carry out gas chromatography?

A

1) small amount of volatile mixture injected into apparatus - gas chromatograph
2) mobile carrier gas carries components of the sample through capillary column (contains liquid stationary phase)
3) components slow down as they interact with stationary phase inside column
4) components are separated depending on solubility in stationary phase

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17
Q

The more soluble the component is in the liquid stationary phase, the ___ it moves through the capillary column.

A

slower

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18
Q

What is retention time?

A

the time taken for each component to travel through the capillary column

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19
Q

What can retention times be used to identify?

A

the components present in the sample by comparing these to retention times for known components

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20
Q

What is a peak integration?

A

the area under a peak

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21
Q

What can peak integrations be used to determine?

A

the concentrations of components in the sample

22
Q

How do you determine the concentration of a component in a sample?

A

1) prepare standard solutions of known concentrations of the compound being investigated
2) obtain gas chromatograms for each standard solution
3) plot calibration curve of peak area against concentration
4) obtain gas chromatogram of compound being investigated under same conditions
5) use calibration curve to measure concentration of compound

23
Q

How do you test for an alkene?

A

add bromine water drop-wise - bromine water decolourises from orange to colourless

24
Q

How do you test for a haloalkane?

A

add silver nitrate + ethanol + warm to 50C in water bath:

1) chloroalkane - white precipitate
2) bromoalkane - cream precipitate
3) iodoalkane - yellow precipitate

25
Q

How do you test for a carbonyl?

A

add 2,4-dinitrophenylhydrazine - orange precipitate

26
Q

How do you test for an aldehyde?

A

add Tollens’ reagent and warm - silver mirror

27
Q

How do you test for a primary/secondary alcohol + aldehyde?

A

add acidified potassium dichromate(VI) + warm in water bath - colour change from orange to green

28
Q

How do you test for a carboxylic acid?

A

add aqueous sodium carbonate - effervescence

29
Q

When is nuclear spin significant?

A

if there is an odd number of nucleons (protons + neutrons)

30
Q

What is resonance?

A

the rapid flipping between two spin states

31
Q

What does NMR stand for?

A

nuclear magnetic resonance

32
Q

What is the frequency required for resonance proportional to?

A

magnetic field strength

33
Q

What does chemical shift measure?

A

the energy needed for nuclear resonance to take place

34
Q

What units is chemical shift measured in?

A

parts per million (ppm)

35
Q

What chemical are all chemical shifts compared to?

A

tetramethylsilane (TMS), (CH₃)₄Si

36
Q

What is the chemical shift value of TMS?

A

0 ppm

37
Q

What does the amount of chemical shift depend on?

A

1) chemical environment

2) nearby electronegative atoms

38
Q

What is a deuterated solvent?

A

a solvent in which the ¹H atoms have ben replaced by ²H atoms (deuterium, D)

39
Q

What information does a carbon-13 NMR spectrum provide?

A

1) number of carbon environments - number of peaks

2) types of carbon environments - chemical shift

40
Q

Do carbon atoms that are bonded to different atoms have the same or different chemical shifts?

A

different

41
Q

Do symmetrical carbon atoms have the same or different chemical shifts?

A

same

42
Q

What information does a proton NMR s pectrum provide?

A

1) number of proton environments - number of peaks
2) types of proton environments - chemical shift
3) number of each type of proton - ratio numbers
4) number of protons adjacent to a given proton - splitting pattern

43
Q

For proton NMR, what does the ratio of areas under each peak give?

A

the ration of number of protons responsible for each peak

44
Q

What is spin-spin coupling/spin-spin splitting?

A

the splitting of a main peak into sub-peaks

45
Q

n + 1 =

A

the number of sub-peaks in a splitting pattern for a proton with n protons attached to an adjacent carbon atom

46
Q

What is the splitting pattern for a peak area of 1?

A

singlet

47
Q

What is the splitting pattern for a peak area of 1:1?

A

doublet

48
Q

What is the splitting pattern for a peak area of 1:2:1?

A

triplet

49
Q

What is the splitting pattern for a peak area of 1:3:3:1?

A

quartet

50
Q

How do you identify -OH + -NH protons?

A

1) run proton NMR spectrum as normal
2) add small volume of deuterium oxide, D₂O + shake + run second spectrum
3) OH peak will disappear

Chemistry OCR A-Level (28 decks)

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