Chapter 13 Flashcards Preview

Chem 5350 > Chapter 13 > Flashcards

Flashcards in Chapter 13 Deck (35):
1

affect of high concentration on Beer's law

solute-solute, solute-solvent, and H bond interactions change how molecule absorbs.

2

problem with chemical dissociation

individual components follow beer's law, but total concentration does not

3

Beer's law only strictly applies with ? sources

monochromatic

4

radiation source usually employed

polychromatic source with grating or filter

5

why is the lamda max chosen as the wavelength when plotting concentration vs absorbance

has least variation from adjacent wavelengths. produces a more linear plot of conc. vs absorbance

6

problems with stray light

limits maximum absorbance

7

two types of instrument limitations

stray light, mismatched cuvettes

8

as concentration increases, deviation from stray light decreases/increases

increases

9

type one noise influence on transmittance

limited readout resolution, heat detector johnson noise, dark current and amplifier noise. Not dependent of transmittance.

10

type two noise influence on transmittance

photon detector shot noise

11

type three noise influence on transmittance

cell positioning uncertainties, source flicker. Linearly dependent on transmittance.

12

type one noise is a usually a result of ?

inexpensive equipment

13

lower slit width =

high absorbance, greater resolution, but increased noise

14

false peaks a result of

transmission of stray radiation

15

light source for UV

h2 or D2 (D2 preferred, much brighter)

16

Use ? cells in UV region

quartz (fused silica)

17

mechanism of production of coninuum spectrum

formation of an excited molecular
species followed by dissociation of the excited
molecule to give two atomic species plus an ultraviolet
photon

18

deuterium wavelength range

160-380.

19

tungsten lamp

used for visible and near-infrared wavelengths. 350-2500nm range. blackbody approximate output (temperature dependent)

20

tungsten-halogen lamp

add small amount of iodine to tungsten lamp. extends life of source as W can redeposit. higher source intensity.

21

Beers law generates linear plot when...

concentrations of analytes are low and using a monochromatic source

22

Problem with polychromatic sources

Analyte can have different molar absorptivity at the different wavelengths. Makes plot less linear if molar absorptivities differ with wavelength.

23

why match cells

so analyte and blank have same reflection

24

When to calibrate at 0% transmittance

dark current (no light passing)

25

When to calibrate at 100% transmittance

with blank

26

shot noise

noise from transfer of electrons across a junction

27

components of Single beam instrument

source, filter or monochromator, cel, photodetector, amplifier, readout

28

Double beam in space components

source, filter or monochromator, lens, beam splitter, reference cell, sample cell, 2 photodetectors, difference amplifier, readout

29

double beam in time components

source, filter or monochromator, sector mirror, reference cell, sample cell, grid mirror, one photodetector, amplifier, readout

30

double beam in space photodetector

takes ratio of P and P0 (T=P/P0)

31

double beam in time example instrument

Varian 100

32

photometer advantage

portable, cheap

33

most commonly used spec? range?

spec 20. 400 to 900nm

34

double dispersing instrument

has 2 monochromators

35

benefits of double dispersing instrument

better res. low stray rad, low noise