Modern analytical chemistry Flashcards

1
Q

Reasons for using analytical techniques

A

Faster
cheaper
more accurate and precise
experiments can be repeated quickly

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2
Q

Structure of compound found using variety of methods/diff observation singularly or in combination

A

.

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3
Q

Describe electromagnetic spectrum

A

Infrared light - low energy, long wavelengths, Red, Orange
towards Ultraviolet - high energy, short wavelengths, Blue-Purple
Middle section = visible region

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4
Q

Diff b/n absorption and emission spectra

how each is produced

A

Emission Spectra - Hot, excited gaseous sample of an element that emits light which can be split through a prism to produce a characteristic emission spectrum
Coloured lines on a black background, converging at the high energy end

Absorption Spectra -
light passed through a cold, unexcited gaseous sample of an element
Electrons within atoms of the sample will absorb light
The remaining light is passed through a prism to produce a characteristic absorption spectrum
Coloured background with black lines

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5
Q

Atomic and molecular processes in which absorption of energy takes place

A

Vibrations
rotations
electronic transitions

symmetric and asymmetric stretching vibrations

Bending vibrations 
- IN-plane rocking
in-plane scissoring
out-of-plane wagging (near/near)
out-of-plane twisting (near/far)
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6
Q

Operating principles of double-beam IR spectrometer

diagram is “sufficient”

A

Light source produced by IR source
Source beam split into separate beams
Travels through sample and reference (control)
E.g. In aqueous sample
Water/solvent used as reference
Allows cancellation of effect of water
segmented rotating disc alternates which two beams pass to the detector
Prism acts as monochromator, selecting correct wavelength of light
Detector compares signlas from both sample and reference
Determines how much absorbance due to sample

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7
Q

How info from IR spectrum is used to identify bonds

A

Wavenumber -
Higher bond enthalpy = more energy = higher wavenumber
More bonds = higher bond enthalpy = higher wavenumber
Larger mass = lower frequency of vibration = lower energy = lower wavelength
Particular functional groups have different absorbance bands

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8
Q

Analyse IR spectra of organic compounds

A

Can identify bonds present, but not always functional groups

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9
Q

Determine molecular mass of a compound from molecular ion peak

A

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10
Q

Analyse fragmentation patterns in a mass spectrum to find structure of a compound

A
Examples:
Mr-15 Loss of Ch3
Mr -17 Loss of OH
Mr - 29 loss of CHO or C2H5
Mr - 31 loss ofCH2O
Mr- 45 loss of COOH

Only picks up radicals (particle with one unpaired electron)

Tallest peak = base peak
Often this is the parent molecular ion (molecule minus e-)

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11
Q

Deduce structure of a compound given information from its HNMR spectrum

A

Number of diff H environments
relative number of H in each environent
Familiar with word and diagram of spectrum, including integration trace

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12
Q

Outline how NMR is used in body scans

A

Protons in water molecules within human cells can be detected by MRI, giving 3D view of organs in the body

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13
Q

State uses of AA spectroscopy

A

Identfication of metals in water, blood, soils and food

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14
Q

Principles of AA

A

Energy absorbed by a metal as electrons are excited is measured.

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15
Q
Use of 
Fuel atomiser
monochromatic light source
monochromatic detector
readout
A

Hollow Cathode Lamp - Monochromatic light source. Emits light of a particular wavelength to be absorbed by the element.

Fuel atomiser - Acetylene-air mixture or nitrous oxide - acetylene mixture (hotter flame)
Vapourised and atomised (metal ions to metal atoms)
Some light absorbed by sample

Monochromator and slit - Remaining non-absorbed light is passed through a monochromator. Isolates one wavelength that is strongly absorbed by element of interest.

Monochromatic detector - Measures the intensity of this wavelength.

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16
Q

Determine concentration of a solution from calibration curve

A

Measure absorbance of unknown

Use standard curve of that metal to determine the concentration of the unknown

17
Q

State reason for using chromatography

A

Used to separate components of a mixture
Identified and then [thing in sample] determined
Mainly used for organic compounds

18
Q

Principles of chromatography

A

All Chromatography techniques involve adsorption on a stationary phase and dissolution into the mobile phase

19
Q

Use of paper chromatography, TLC and column chromatography

A

Paper -
Thing layer of water bound to a piece of high quality absorbent paper
TLC -
A thin layer of absorbent material (Silica/aluminaA) spread onto glass or plastic plate
Both stationary phases are polar in paper/tlc
Capillary action pulls liquid up

Rf value - Retardation factor
Distance moved by component/distance moved by solvent

Column chromatography - Stationary phase, solid/solid that has been thinly coated in viscous liquid and packed into glass/plastic column
Sample applied to top of column, solvent (mobile phase) is dripped through the column.
Tap at bottom alloows solvent to elute from column at same rate as enters.
Separation occurs same as paper/tlc just components can be collected.

20
Q

Describe effect of different ligands on splitting of d orbitals in transition metals

A

CN->NH3>H2O>Cl-

21
Q

Factors that affect colour of transition metals

A

Nature of metal ion - charge/ionic radii influences distance/attraction between ligand and ion

Charge of transition metal ion - Greater charge, greater attraction, INCREASED splitting of d-orbitals

Size of ligand - Smaller ligand, closer lone pairs can get to d-orbital of ion. repulsion INCREASES splitting of d-orbitals

Shape of complex ion - d-orbitals of transition metal ion in a tetrahedral shape complex split differently to those in octahedral complex.

22
Q

Organic molecules containing a double bond absorb UV radiation

A

Conjugated and delocalised systems

Inc. Arenes, alkenes and chlorophyll

23
Q

Effect of conjugation of double bonds in organic molecules on the wavelength of absorbed light

A

Energy difference between molecular orbitals decreases, and the wavelengths of light absorbed increase.
As conjugation increases, differences between molecular orbital energies decreases and the light that is absorbed enters the visible range.

24
Q

Predict whether a molecule will absorb UV or visible radiation

A

Difference in energy levels small: More conjugation = visible radiation
Energy difference in levels large: double bonds/triple bonds = UV radiation

25
Q

Determine concentration of a solution from a calibration curve using the Beer Lambert Law

A

The amount of absorbance of a subtance at a particular wavelength is proportional to the concentration of the substance.

26
Q

Explain use of tetramethylsilane (TMS) as reference std

A

Same chemical/proton environment.
Safe
Far away from most other substances to be analysed

27
Q

Analyse HNMR spectra

A

Number of peaks
area under peaks
chemical shift
splitting patterns

Familiar with singlets, doublets, triplets and quartets

28
Q

Describe techniques of gas-liquid chromatography GLC and high performance liquid chromatography HPLC

A

HPLC - particles in column are much smaller. Better separation of similar compounds. Generally pumped through under high pressure. Stat phase = Solid silica spheres

GLC - Compounds that can be vapourised without decomposing.

29
Q

Deduce which chromatographic technique is most appropriate for separating components in a mixture

A

HPLC used for temp sensitive
Oil, alcoholic beverages, antioxidants, sugars/vitamins in food, pharmaceuticals, molymers, biochemical/biotechnology research, quality control of insecticides and herbicides

GLC identify compounds that can vaporise without decomposing
Urine samples in athletes, underground mine gases, blood alcohol levels