UV-Vis Spectroscopy

Question 1

The electromagnetic Spectrum

HIGH Frequency(v), HIGH Energy
|
V
LOW Frequency(v), LOW Energy

Answer 1

X-RAY

UV

INFRARED

MICROWAVE

RADIO

FREQUENCY

Question 2

___ has many different applications in ORGANIC and BIOLOGICAL CHEMISTRY

Most basic of these application is the use of the ___ to deptermine the concentration of a ___.

Answer 2

UV-Vis Spectroscopy

Beer-Lambert Law

Chromophore

Question 3

Part of the molecule where the ABSORPTION occurs and where the main change of the geometry or electron density, etc. appears after the excitation process.

Answer 3

Chromophore

Question 4

The ___ is the application of the observation that, within CERTAIN RANGES, the ABSORBANCE of a chromophore at a given WAVELENGTH VARIES in a linear fashion with its CONCENTRATION

TLDR; HIGHER CONCENTRATION, GREATER ABSORBANCE

Is what makes SPECTROPHOTOMETRIC DETERMINATION of ORGANIC COMPOUNDS feasible

Answer 4

Beer-Lambert Law

Question 5

True or False: Inorganic species cannot absorb

Answer 5

FALSE, a number of inorganic species can absorb

many IONS of the TRANSITION METALS are COLORED in solution and can thus be determined by spectrophotometric measurement.

Question 6

SPECIES that show CHARACTERISTIC ABSORPTION BANDS (6)

Answer 6

NitrITE

NitrATE

Chromate IONS

OXIDES of NITROGEN

Halogens

Ozone

Question 7

___ can be determined photometrically by causing them to react with ___ to produce products that ABSOR STRONGLY in UV and VISIBLE regions.

Answer 7

non-absorbing analytes

chromophoric reagents

Question 8

The successful application of these COLOR-FORMING REAGENTS usually requires that their REACTION with the ANALYTE be forced to ___ unless they use methods such as KINETIC methods.

Answer 8

NEAR COMPLETION

Question 9

Typical INORGANIC REAGENTS for NON ABSORBING:

Thiocyanate ion for (3)

Answer 9

Iron

Cobalt

Molybdenum

Question 10

Typical INORGANIC REAGENTS for NON ABSORBING:

Hydrogen Peroxide for (3)

Answer 10

Titanium

Vanadium

Chromium

Question 11

Typical INORGANIC REAGENTS for NON ABSORBING:

Iodide ion for (3)

Answer 11

Bismuth

Palladium

Tellurium

Question 12

____ that FORM STABLE COLORED COMPLEXES WITH CATIONS are even more important.

Answer 12

Organic chelating reagents

Question 13

Common examples for ORGANIC CHELATING REAGENTS for NON ABSORBING:

Copper

Lead

Iron

Nickel

Answer 13

Common examples for ORGANIC CHELATING REAGENTS for NON ABSORBING:

Copper - Diethyldithiocarbamate

Lead - Diphenylthiocarbazone

Iron - 1,10 Phenanthroline

Nickel - Dimethylglyoxime

Question 14

particularly important for quantitative analysis because MOLAR ABSORPTIVITIES are unusually LARGE

(e > 10,000 L mol-1 cm-1 ), which leads to HIGH SENSITIVITY.

Many INORGANIC and ORGANIC complexes exhibit this TYPE OF ABSORPTION and are therefore called ____

consists of an ___ bonded to an ___

Answer 14

charge-transfer complexes

electron-donor group, electron acceptor

Question 15

When a CHANGE-TRANSFER COMPLEX absorbs radiation, an ____ from the DONOR is transferred to the ____ that is largely associated with the ACCEPTOR.

The EXCITED STATE is this the product of a kind of INTERNAL ___ / ___ process

This behavior DIFFERS FROM ORGANIC CHROMOPHORE in which the excited electron is in a molecular orbital that is shared by ___.

Answer 15

Electron , Orbital

Oxidation / Reduction

two or more atoms

Question 16

TYPICAL INSTRUMENTS:

use a FILTER FOR WAVELENGTH SELECTION in conjunction with a suitable RADIATION TRANSDUCER (converts a signal or light into a current or voltage).

have the advantages of SIMPLICITY, RUGGEDNESS, and LOW COST; most often used for the ___; good signal-to-noise ratio.

find considerable use as detectors for chromatography, electrophoresis, immunoassays, or continuous flow analysis.

Answer 16

Photometers

VISIBLE REGION

Question 17

Offer the considerable advantage that the WAVELENGTH USED CAN BE VARIED CONTINUOUSLY, making it possible to record ____

cover the ___ and occasionally the ___region

Answer 17

Spectrophotometers

Absorption Spectra

UV/visible , near-infrared

Question 18

TO FIND IDENTITY of the absorbing groups by COMPARING the spectrum of an ANALYTE with those of ___ containing various ___.

Answer 18

SIMPLE MOLECULES

chromophoric groups

Question 19

TRUE or FALSE: ultraviolet spectra have sufficient fine structure to permit an analyte to be identified

Answer 19

FALSE, ultraviolet spectra do not have sufficient fine structure to permit an analyte to be identified unambiguously.

ultraviolet qualitative data must be supplemented

Question 20

Evidence that supplements UV qualitative data: (6)

Answer 20

Infrared

Nuclear Magnetic Resonance

Mass Spectra

Solubility

Melting

Boiling point

Question 21

Important characteristics of SPECTROPHOTOMETRIC and PHOTOMETRIC methods

Answer 21

Wide applicability

High Sensitivity

Moderate to High Selectivity

Good Accuracy

Ease and Convenience

Question 22

WIDE APPLICABILITY:

Nonabsorbing species can also be determined after ____ .

Large majority of determinations performed in clinical laboratories

Answer 22

chemical conversion to absorbing derivatives

Question 23

HIGH SENSITIVITY:

TYPICAL DETECTION LIMITS for absorption spectroscopy range from ___; can be extended to ___ with procedural modifications.

Answer 23

10^-4 to 10^-5 M

10^-6 or even 10^-7 M

Question 24

MODERATE TO HIGH SELECTIVITY:

Often a WAVELENGTH can be found at which THE ANALYTE ALONE ABSORBS

HOWEVER, ___ DO OCCUR, corrections based on ADDITIONAL MEASUREMENTS AT OTHER WAVELENGTHS sometimes ELIMINATE THE NEED for a separation step.

When SEPARATIONS are required, spectrophotometry often DETECTS THE SEPARATED SPECIES

Answer 24

Overlapping Absorption bands

Question 25

GOOD ACCURACY:

The relative errors in concentration encountered lie in the range from ___. Such errors can often be decreased to a FEW TENTHS OF A PERCENT W/ SPECIAL PRECAUTIONS

Answer 25

1% to 5%

Question 26

PROCEDURAL DETAILS: (6)

Answer 26

(a) Wavelength Selection.

(b) Variables That Influence Absorption.

(c) The Relationship between Absorbance and Concentration

(d) The Standard Addition Method.

(e) Analysis of Mixtures.

(f) Photometric and Spectrophotometric Titrations

Question 27

(a) Wavelength Selection.

For MAXIMUM SENSITIVITY, spectrophotometric absorbance measurements are usually made at the ____ because the ____ is greatest at this
point.

In addition, the ABSORPTION CURVE is often ___ at a maximum, leading to good adherence to BEER’S LAW and less uncertainty from failure to reproduce precisely the wavelength setting of the instrument.

Answer 27

wavelength of maximum absorption

change in absorbance per unit of concentration

flat

Question 28

(b) Variables That Influence Absorption.

The effects of these 5 variables must be known so absorbance will not be materially affected

Answer 28

 nature of the SOLVENT,
 the pH of the solution,
 the TEMPERATURE,
 high ELECTROLYTE concentrations,
 the presence of INTERFERING SUBSTANCES.

Question 29

(c) The Relationship between Absorbance and Concentration.

CALIBRATION STANDARDS should approximate as closely as possible the OVERALL COMPOSITION OF THE ACTUAL SAMPLES and encompass a reasonable range of analyte concentrations.

CALIBRATION CURVE is usuallly ABSORVANCE BERSUS CONCENTRATION OF SEVERAL STANDARDS to evaluate the relationship.

HOWEVER, only a SINGLE STANDARD is used to determine ___.

Unless there is no other choice, it is NEVER GOOD to base the results of a determination solely on a ____ for the (answer above).

Answer 29

Molar absorptivity

literature value

Question 30

When two or more compounds do not chromatographically separate

Answer 30

Co-eluting

Question 31

(d) The Standard Addition Method.

Used when ___ are a problem due to co-eluting compounds. It usually improves results by providing compensation for these effects.

For example, the ABSORBANCE of many ___ is DECREASED in the presence of ___ and ___ because of the tendency of these ANIONS FORM COLORLESS COMPLEXES WITH METAL IONS (the color formation
reaction is often LESS COMPLETE, thus sample ABSORBANCE LOWERED).

Ideally, the composition of calibration standards should approximate the composition of the samples to be analyzed (NOT ONLY FOR ANALYTE CONCENTRATION but also CONCENTRATION OF THE OTHER SPECIES IN THE SAMPLE MATRIX)

Answer 31

Matrix effects

Colored complexes of metal ions

sulfate , phosphate ions

Question 32

(e) Analysis of Mixtures.
 The TOTAL ABSORBANCE OF A SOLUTION at any givenwavelength is equal to the ___ in the solution.

 This occurs completely even with spectra overlap.

Answer 32

sum of the absorbances of the INDIVIDUAL COMPONENTS

Question 33

F. Photometric and Spectrophotometric Titrations

 useful for locating the ___ of titrations.
 requires one or more of the reactants or products ___ or that an ___ be added to the analyte solution.

Answer 33

equivalence points

absorb radiation

absorbing indicator

Question 34

TITRATION URVES of a PHOTOMETRIC TITRATION

 plot of absorbance (corrected for volume change) as a function of titrant volume.
 If conditions are chosen properly, the curve consists of___,

◼ one occurring ___ of the
titration
◼ the other located ___ region.

The end END POINT is taken as the INTERSECTION of extrapolated linear portions of the two lines.

Answer 34

two straight-line regions with different slopes

prior to the equivalence point

well beyond the equivalence-point