Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

instrumental analysis > mst deck > Flashcards

mst deck Flashcards

1
Q

what’s the difference between quantitative and qualitative analysis?

A 
qualitative = what is in a sample
quantitative = how much is in a sample
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

6 stages of analytical process

A
  1. definition
  2. sampling
  3. selecting method of analysis
  4. sample preparation
  5. quantitation
  6. presentation and evaluation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

define sampling

A

obtaining a small fraction of material from a large bulk such that the fraction is representative of the bulk in every way

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

3 considerations when deciding method of sampling

A
  1. size of gross sample
    a. heterogeneity
    b. accuracy/precision desired
    c. cost of sampling
  2. physical state of fraction to be analysed: solid, liquid, gas
  3. chemical composition of material to be analysed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

4 conditions for storing samples

A
  1. storage container is clean and airtight
  2. avoid adsorption effect on walls of containers esp for analysis of trace metals
  3. store in rooms not too hot and humid
  4. avoid prolonged periods of storage time to prevent decomposition/evaporation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

define wavelength

A

distance of one complete cycle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

wave number formula and unit

A

1 / λ

unit: cm^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

define frequency

A

number of cycles passing a fixed point per unit time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

velocity formula

what is the speed of light

A 
v = f x λ
c = 3.0 x 10^8 m s^-1
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

energy formula

A

E = hf or hv/λ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

define absorption

A

process where atoms or molecules acquire certain discrete quantise amounts of energy from incoming radiation and become excited

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is a photon/quanta

A

minute, discrete amount of energy of electromagnetic radiation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

difference between atomic and molecular spectrum

A

when atoms absorb radiation, only electrons get excited = only electronic transition

molecules absorb whole lines of radiation, and have 3 processes of absorbing energy: rotational, vibrational, electronic transition

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

transmittance and absorbance formulae

A 
T = I / I0
A = log10 (1 / T)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Beer-Lambert law

A

A = abc or εbc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

2 assumptions of Beer-Lambert law

A
  1. monochromatic light is used: only a single wavelength is employed in absorbance measurement
  2. there are no concentration-dependent interactions present: each absorbing particle absorbs independently of each other, true in very dilute solution i.e. < 10-3 M
17
Q

2 deviations of Beer-Lambert law

A

true deviation: when concentration is so high that refractive index changes from that of blank, affecting values of a / ε

apparent deviation: when nature or concentration of absorbing species changes, causing non-symmetrical chemical equilibria and hence nonlinearity.

18
Q

4 major components of a uv-vis spectrometer

A
  1. radiation source (deuterium lamp for ultraviolet, tungsten lamp for visible)
  2. monochromator (prism or diffraction grating)
  3. sample cell (quartz for both, glass for visible)
  4. detector (photocell or photomultiplier)
19
Q

compare pros and cons of single and double-beam uv-vis spectrometer (3)

A
  1. single-beam: risk of analytical error from line voltage changes resulting in fluctuation in intensity of radiation reaching detector; double-beam: beam ratio is obtained and used constantly, minimising analytical error
  2. single-beam: risk of analytical error from solvent absorbing some radiation; double-beam: analytical error is corrected
  3. both single and double-beam: risk of analytical error from loss of radiation at reflecting surfaces
20
Q

describe procedure for selection of wavelength and obtaining calibration graph in uv-vis spectrometry (2)

A
  1. spectrum scan:
    conduct spectrum scan at from 800 to 200 nm
    take wavelength at highest absorbance = highest sensitivity = ideal choice
  2. photometric scan:
    conduct photometric analysis at λmax to obtain calibration graph
21
Q

what are the quantitative applications of uv-vis spectrometry (2)

A
  1. spectrum scan: to determine wavelength that can be absorbed appreciably by sample
  2. photometric scan: determine unknown concentration of sample
22
Q

what are the qualitative applications of uv-vis spectrometry (3)

A
  1. detect presence or absence of certain functional groups
  2. detect impurities
  3. identification by matching spectra of unknown and standard
23
Q

what are the problems with qualitative analysis using uv-vis spectrometer? (2)

A
  1. broad spectrum gives little details

2. spectra of different compounds may overlap to give complex spectrum

24
Q

what are chromophores?

A 
functional groups that can absorb radiation in uv-vis region i.e.
π electrons (multiple bonds) or
n electrons (N, O, S, halogens)
25
Q

4 components of infrared spectrometer

A
  1. radiation source (Nernst Glower or Globar)
  2. monochromator (except FT-IR which uses interferometer)
  3. sample cell (metal halide)
  4. detector (bolometer or thermocouple)
26
Q

3 conditions for radiation source of infrared spectrometer

A
  1. must be able to emit radiation over infrared region i.e. 400-4000 cm^-1
  2. must have sufficient intensity such that transmitted energy can be detected at the end of the optical path
  3. must be stable (I0 = 100%)
27
Q

3 conditions for radiation source of uv-vis spectrometer

A
  1. must be able to emit radiation over uv-vis region i.e. 800 to 200 nm
  2. must have sufficient intensity such that transmitted energy can be detected at the end of the optical path
  3. must be stable (I0 = 100%)
28
Q

3 problems with using metal halides as sample cell/prism in infrared spectrometer

A
  1. mechanical instability
  2. thermal instability
  3. water solubility
29
Q

how to prepare samples for infrared spectrometry for solid (3), liquid (2) and gas (1)

A

solid sample preparation

  1. KBr pellet technique
  2. mull technique
  3. cast film technique

liquid sample preparation

  1. KBr disc technique
  2. liquid cell technique (CaF2 is used if water is present in sample)

gas sample preparation
KBr or NaCl sample cell technique
*difficult to analyse as concentration is low. we can use a cell with longer path length, which will increase absorbance.

30
Q

theory of infrared absorption (2)

A

each molecule has a complete absorption spectrum unique to its functional groups.

in molecules, atoms are held by chemical bonds and are in continuous synchronised movement.

31
Q

3 conditions for molecule to absorb infrared radiation

A
  1. change in bond length or angle due to vibrational or rotational motion causing net change in dipole moment
  2. molecule must be vibrating at a natural frequency equal to frequency of incoming radiation
  3. radiation energy must correspond to energy difference between ground state and excited state of molecule
32
Q

4 precautions when doing sample treatment/sample preparation

A
  1. should be done without losing any of the analytes
  2. should be done without adding new interferences
  3. should bring analyte into appropriate chemical form for method to be used
  4. should dilute/concentrate analyte for detectable results by the instrument

instrumental analysis (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions