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Chemsitry > Analytical > Flashcards

Analytical Flashcards

1
Q

What is flight mass spectrometry

A

Where the elements in a compound are discovered via their mass

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2
Q

What are the stages of mass spec

A

Vaporisation
Ionisation
Acceleration
Time of Flight
Detection

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3
Q

What is vaporisation in mass spec

A

Dissolve the sample in a volatile solvent
Reduces pressure

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4
Q

What is ionisation in mass spec

A

Bombard sample with high energy elections, knocking off electrons to form 1+ charge
Fragmentation May also occur

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5
Q

What is acceleration in mass spec

A

Using the electric field to accelerate ions to give them equal kinetic energy

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6
Q

What is the equation for kinetic energy

A

Ke = 1/2 x m x v(squared)

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7
Q

What is time of flight in mass spec

A

Ions with different masses travel with different velocities

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8
Q

How does Carbon 13 NMR work

A

The difference in magnetic field between an atom with odd numbers of electrons and a large magnetic field can be measured by the absorption of radio waves to flip the nucleus

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9
Q

What atoms can be detected by NMR

A

H, C13

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10
Q

Why is a solvent used in NMR

A

To dissolve the organic substance without interfering with the spectrum

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11
Q

What are two commonly used NMR solvents

A

CCl4 (tetrachloromethane)
CDCl3 (deuterated brichloromethane)

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12
Q

How is NMR calibrated

A

The use of tetramethylsilane (TMS) creates a single peak at 0, so all other peaks are positioned relative to it

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13
Q

Why is TMS used

A

Generates a single peak in C13 and H NMR
Peak lies to right hand side of spectrum
Unreactive
Low boiling point so easy to remove from sample
Non toxic

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14
Q

What is the formula of TMS

A

C4H12Si

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15
Q

What does the number of peaks in C13 NMR tell us

A

The number of different carbon environments

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16
Q

What affects the height of peaks in C13 NMR

A

The more C atoms in that environment, the higher the peak

17
Q

What does the position of peaks tell us in C13 NMR

A

The type of chemical environment

18
Q

What does the number of signals in proton NMR show us

A

The number of hydrogen environments

19
Q

What does the intensity of the peak show in proton NMR

A

The number of hydrogen atoms in the environment

20
Q

What does the chemical shift(position of peak) show

A

The type of chemical environment

21
Q

What is the reference chemical for proton NMR

A

TMS

22
Q

What does the shape of peaks show in proton NMR

A

The number of adjacent hydrogens

23
Q

How can high resolution NMR chemical shift be calculated

A

Field for TMS - field of sample/ field for TMS x 10-6 ppm

24
Q

How does high resolution proton NMR differ from other NMR

A

Signals in high res H1 NMR are split, caused by the interactions of magnetic fields on hydrogen ions in neighbouring carbon atoms

25
Q

What rule dictates the number of lines a signal is split into

A

Hydrogens on neighbouring atoms + 1

26
Q

What determines retention time in gas chromatography

A

The higher the affinity for the stationary phase, the longer the retention time

27
Q

What is the acidified dichromate test

A

Tests for alcohol

28
Q

What is the result of the potassium dichromate test

A

Orange to green in presence of an alcohol

29
Q

What alcohols turn green on the addition of potassium dichromate

A

Primary and Secondary

30
Q

How does the Schiffs reagent test work

A

Warm the reaction mixture, then pass the vapours through cold Schiffs reagent

31
Q

What are the results of Schiffs reagent

A

If Schiffs reagent turns magenta, it is a primary alcohol, if there’s no colour change it’s a secondary alcohol

32
Q

What is the stationary phase for thin layer chromatography

A

Silica plate

33
Q

What is the mobile phase for thin layer chromatography

A

Liquid solvent

34
Q

What is the stationary phase for paper chromatography

A

High quality filter paper

35
Q

What is the mobile phase for paper chromatography

A

Liquid solvent

36
Q

What affects the rate at which a substance moves up the plate in TLC

A

Solubility of substance in solvent

Attraction between solute and stationary phase

37
Q

What is the use of a watch glass in TLC

A

Prevents evaporation of solvent

38
Q

What must the pencil be in TLC

A

Insoluble so as not to affect the results

39
Q

Where must the solvent level be in TLC

A

Solvent level below the pencil line to prevent washing off substance

Chemsitry (15 decks)

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