5. Light absorption

Question 1

What is light absorption?

Answer 1

absorption of light photons in matter. On the atomic scale, the energy of the absorbed photon is used for the excitation of the outer-shell electrons.

Question 2

Light that passes through a layer of matter is attenuated as a result of ___ (2 things)

Answer 2

light absorption and scattering.

Question 3

What is absorbance (A)?

Answer 3

base-10 logarithm of the ratio of the perpendicularly incident (J0) and perpendicularly transmitted (J ) light intensity ( log (J0 / J ) ). The three different names are used for the same physical quantity.

Question 4

What is Transmittance (T)?

Answer 4

transmission coefficient is defined as the following ratio of intensities

Question 5

Other names for absorbance

Answer 5

EXTINCTION (E), OPTICAL DENSITY (OD)

Question 6

The absorption spectrum of atoms and molecules is closely related to their __

Answer 6

electronic structure.

Question 7

If we provide a ground-state electron with energy corresponding exactly to the difference between the excited- (E2) and ground-state (E1) energies, then the electron jumps to the ___

Answer 7

excited state

Question 8

s. If we provide a ground-state electron with energy corresponding exactly to the difference between the excited- (E2) and ground-state (E1) energies, then the electron jumps to the excited state.

→ How much photons absorbed in the system?

Answer 8

Thus, if a system of molecules is illuminated with light of matching photon energy (wavelength, color), the system absorbs part of these photon

Question 9

From the excited state the system will return to the ground state, loosing its excess energy.

→ In most cases this process involves ___

Answer 9

heat exchange with the environment in many small steps (relaxation).

Question 10

What is absorption coefficient?

Answer 10

the attenuation coefficient characteristic for the type of the material and for the wavelength of light,

Question 11

What is MOLAR EXTINCTION COEFFICIENT?

Answer 11

a quantity characteristic of the absorption by the material.

• It depends on the wavelength and on the characteristics of the material.
• It gives the optical density of the solution of unit concentration and unit layer thickness. (It does not depend on the concentration and thickness of the material).

Question 12

What is BEER-LAMBERT LAW?

Answer 12

an expression, valid for dilute solutions, stating that the absorbance of the solution is proportional to the concentration (c) and to the thickness of the material → the proportionality factor is the molar extinction coefficient

Question 13

What is absorption spectrum?

Answer 13

absorbance is plotted as a function of wavelength.

Question 14

On the atomic scale, the energy of the absorbed photon is used for _____

Answer 14

excitation of the outer-shell electrons.

Question 15

Which coefficient characterizes the type of material?

Answer 15

the attenuation coefficient

Question 16

Which coefficient characterizes the wavelength of light?

Answer 16

absorption coefficient

Question 17

In case of dilute solutions, if the solvent does not absorb in the applied wavelength range (i.e., it is transparent, just like water or alcohol in the visible range), then the absorption coeffi- cient is _____ to the concentration of the solute

Answer 17

Proportional

Question 18

What does molar extinction coefficient (extinc- tion coefficient for short) depend on?

Answer 18

• wavelength
• characteristics of the material.

(It does not depend on the concentration and thick- ness of the material).

Question 19

the Beer-Lambert Law is only valid for ____

Answer 19

Dilute solutions

Question 20

What are complementary colors?

Answer 20

a pair of colors that gives white light as a result of additive color mixing.

• Such pairs are for example: yellow-blue, green-red, etc.
• The color of a material apparent from reflected or transmitted light will be the complementary color of the absorbed one.

Question 21

The location of the absorption maxima (there may be more than one) is related to the ____

Answer 21

electron excitation ener- gies characteristic for the molecular structure

Question 22

• *The ____ of the absorption maximum changes _____ with the _____, provided that the thick- ness stays constant**
• *=> This proportionality is used for _____**

Answer 22

Height

Proportionally

Thickness

Concentration determination

Question 23

The equipment used to measure absorption spectra is called ____

Answer 23

absorption spectrometer

Question 24

In the simple, manual spectrophotometer, the absorbance of the (1)___ and that of the (2)___ are measured separately at every wavelength, which is set manually.

Answer 24

1. sample
2. reference (solvent)

Question 25

DEMONSTRATION MEASUREMENT - THE AB- SORPTION SPECTRUM OF HEMOGLOBIN

What are the 3 tasks?

Answer 25

1. sample
2. reference (solvent)

Question 26

DETERMINATION OF THE CONCENTRATION OF COPPER ION VIA COMPLEX FORMATION

Series of the solutions are made so that known concentrations of a ligand is added (cL) to the metal-ion solution of unknown concentration (cM).

This way we obtain a series of solutions with (1) _____ complex concentration (cC).

Complex concentration (2)____ only until there is (3)___ metal ion available.

Further addition results in (4) ____ ligand concentration. Accordingly, complex concentra- tion (cC) reaches (5) ____ and hence the ab- sorbance reaches a (6) ____ as ligand concentra- tion (cL) is increased

Answer 26

(1) increasing
(2) increases
(3) free
(4) excess
(5) saturation
(6) plate

Question 27

In the simple, manual spectrophotometer, the absorbance of the (1)___ and that of the (2)___ are measured separately at every wavelength, which is set manually.

Answer 27

1. sample
2. reference (solvent)