Chapter 18

Question 1

Defined as A = log(Po/P), where Po is the radiant power of light (power per unit area) striking the sample on one side and P is the radiant power emerging from the other side. Also called optical density

Answer 1

Absorbance, A

Question 2

A graph of absorbance of light versus wavelength, frequency, or wavenumber

Answer 2

Absorption spectrum

Question 3

Relates the absorbance, A, of a sample to its concentration, c, pathlength, b, and molar asorbitivity, ε: A = εbc

Answer 3

Beer’s law

Question 4

The part of a molecule responsible for absorption of light of a particular frequency

Answer 4

Chromophore

Question 5

A cell with transparent walls used to hold samples for spectrophotometeric measurements

Answer 5

Cuvet

Question 6

The whole range of electromagnetic radiation, including visible light, radio waves, X rays, etc

Answer 6

Electromagnetic spectrum

Question 7

Any state of an atom or a molecule having more than the minimum possible energy

Answer 7

Excited state

Question 8

The number of cycles per unit time for a repetitive event

Answer 8

Frequency (n)

Question 9

State of an atom or a molecule with the minimum possible energy

Answer 9

Ground state

Question 10

Process of adding a chemical substance (a masking agent) to a sample to prevent one or more components from interfering in a chemical analysis

Answer 10

Masking

Question 11

Constant of proportionality in Beer’s law: A = εbc, where A is absorbance, b is pathlength, and c is the molarity of the absorbing species; tells us how much sight is absorbed at a particular wavelength by a particular substance. Also called extinction coefficient

Answer 11

Molar absorptivity (ε)

Question 12

Light with a very narrow range of wavelengths (“one color”)

Answer 12

Monochromatic light

Question 13

A device (usually a grating or prism) that disperses light into its component wavelengths and selects a narrow band of wavelengths go pass through the exit slit

Answer 13

Monochromator

Question 14

A solution prepared from all of the reagents except analyte; measures the response of the analytical method to impurities in the reagents or any other effects caused by any component other than the analyte; is not subjected to all preparation steps before analysis

Answer 14

Reagent blank

Question 15

One in which absorption or emission of light is used to monitor the progress of the titration reaction and to find the equivalence point

Answer 15

Spectrophotometric titration

Question 16

In a broad sense, any method using light to measure chemical concentrations

Answer 16

Spectrophotometry

Question 17

The fraction of incident radiation that passes through a sample. Defined as T = P/Po, where Po is the radiant power of light striking the sample on one side and P is the radiant power of light emerging from the other side of the sample

Answer 17

Transmittance (T)

Question 18

Distance between consecutive crests of a wave

Answer 18

Wavelength (λ)

Question 19

Addition of a known compound (usually at a known concentration) to an unknown. In isotope dilution mass spectrometry, the spike is the added, unusual isotope

Answer 19

Spike

Question 20

A technique in which an analytical signal due to an unknown is direst measured. Then a known quantity of analyte is added, and the increase in signal is recorded. From the response, it is possible to calculate what quantity of analyte was in the unknown

Answer 20

Standard additions method

Question 21

A change in analytical signal caused by anything in the sample other than analyte

Answer 21

Matrix effect