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A level Chemistry > Chapter 29 - Chromatography and Spectroscopy > Flashcards

Chapter 29 - Chromatography and Spectroscopy Flashcards

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1
Q

Why is chromatography used?

A

to separate indiv components in a mixture of substances

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2
Q

All forms of chromatgraphy?

A

have a mobile and stationary phase

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3
Q

TLC: stationary phase

A

either SiO2 (s) or Al2O3 on coat TLC plate. IONIC

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4
Q

TLC: what is the stationary phase held on ?

A

plastic or Al sheet

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5
Q

TLC: mobile phase?

A

mixture of solvents

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6
Q

TLC: origin line must be?

A
  • in pencil

* above solvent

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7
Q

TLC: Rf equation?

A

Retardation factor: distance moved by component/ distance moved by solvent front (always <1)
• depends on the solvents and stationary phase used

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8
Q

TLC: smaller Rf value means?

A

the component bonds more strongly to the stationary phase (more polar/ charged)

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9
Q

in the developing tank, why is there filter paper?

A
  • filter paper soaked in solvent to saturate the air inside w the solvent
  • helps solvent travel against gravity up the plate
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10
Q

to determine which substances are in the compound from a chromatogram ?

A

look at spots on the same level

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11
Q

can use chromatogram to determine?

A

purity - only 1 spot

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12
Q

how to visualise spots on a chromatogram - not all are coloured?

A
  • can use UV light/ chemicl stains
  • Solvent needs to be evaporated b4
  • use iodine chamber
  • leave the plate in the chamber for at least 5 mins
  • once removed, as the iodine fades the spots’ll become visible
  • circle spots w pencil before they fade
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13
Q

how does iodine help to visualise?

A
  • warm beaker so it vaporises- sublimes

* iodine is covalent so can bond to the surface of the components (covalent) so dark brown spots appear

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14
Q

gas chromatography: oven

A
  • regulates temp
  • needs to be correct temp - middle of teh BP range
  • KEEPS COMPONENTS AS GASES
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15
Q

gas chromatography: gas cylinder

A

He or N - unreactive mobile phase

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16
Q

gas chromatography: gas flow container valve

A
  • to control the gas flow time through the column

* controls rate at which gas flows thru the column

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17
Q

gas chromatography: sample injection

A
  • if liquid, the sample needs to be heated to vaporise it as it enters the column
  • volatile organic chemicals - have to be a gas - GAS C
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18
Q

gas chromatography: recorded and computer

A

Records the gas chromatogram as a series of peaks - higher peaks = higher quantity

19
Q

gas chromatography: detector

A

detects the organic chemicals not N/He. Connected to a computer

20
Q

gas chromatography: column

A
  • either an oily liquid (alkane) coating the inside of the thin tube/ covering the surface of tiny unreactive beads
  • stationary phase
21
Q

What is gas chromatography used for?

A

separating volatile organic compounds in a mixture

22
Q

GC: stationary phase?

A

oily hydrocarbon (usually long chain alkane) which is held on inert plastic tubing/ inert solid beads in column (usually silica beads)

23
Q

GC: mobile phase?

A

unreactive gas - N or noble gas

24
Q

GC: separation by

A

solubility in oily hydrocarbon - stationary phase

25
Q

GC: retention time

A

number of peaks SUGGESTS how many components are in the mixture

26
Q

GC: what is retention time?

A

time from injection of MIXTURE to detection of COMPONENT

27
Q

GC: what are peak integration areas?

A

calculated by computer = area under each peak. Gives idea of amount of each component.

28
Q

GC: smaller retention time means?

A
  • that compound is less soluble in the stationary phase (alkane)
  • thfr, the compound is likely to be more polar
29
Q

GC: smaller peak integration areas means?

A

less of the component in the mixture

30
Q

GC: negative!

A

• e.g. 3 peaks suggests 3 components

7 but, 2 components could be equally soluble in the SP so 1 peak could actually represent 2 components

31
Q

smallest retention time =

A

least soluble

32
Q

GC and MS

A
  • gas/ liquid chromatography separates the components
  • mass spec produces a distinctive fragmentation pattern for each component
  • identification by a computer using a spectral database
33
Q

when trying to figure out the solubility and RT of a substance think abt

A

SA - larger SA = shorter RT

34
Q

NMR basics

A
  • molecules placed in strong magnetic field and irritated wit radio frequency EM radiation
  • At certain radio wave frequencies, the nuclei of some atoms in the molecules absorb the radio waves
  • These absorptions called resonances (the nuclei are flipping w/against the MF) are used to identify the atoms, count them and work out their position in the molecule
  • NMR focuses on the H/C environments in a compound
35
Q

Use of NMR spectroscopy?

A

MRI scanners

36
Q

which 2 isotopes are most commonly studied in organic chem using NMR?

A

H and C13 - both have an odd number of nucleons

37
Q

why are EMs used in NMR?

A

Nuclei align w/against the MF

38
Q

What is chemical shift?

A
  • δ (measured in ppm)
  • place in the spectrum where the nucleus absorbs radio wave energy
  • This depends on how the atom is bonded in a molecule. This gives us the type of C&H.
39
Q

what is TMS?

A

• stands for tetramethylsilane - the standard refrence signal
(CH3)4Si

40
Q

What is special about MS in NMR?

A
  • 12 equiv protons, 4 equiv carbons which gives a singal sharp peak, defined as δ =0 ppm (reference peak)
  • It’s chemically unreactive so doesn’t interfere w the chemical being analysed
41
Q

which H isotope doesn’t give a signal in proton NMR?

A

• Deuterium nucleus - 2 1 H (even no. of nucleons so no signal)

42
Q

the solvent used in NMR?

A
  • Deuterated trichloromethane - CDCl3

* which is usually used for both proton and carbon NMR

43
Q

How is CDCl3 used in NMR?

A

• 13C spectrum run for the one peak, can be subtracted from the spectra

44
Q

D2O is?

A

deuterium oxide

A level Chemistry (39 decks)

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