Activity No. 5

Question 1

Absorption of IR excites a particular bond or part of the molecule which causes

Answer 1

the atoms to vibrate with each other

Question 2

what is the nature of the vibration of the atoms

Answer 2

bending or stretching that causes a change in the dipole moment of the molecule

Question 3

_____of absorption is proportional to the __________ that the vibration imparts on the molecule

Answer 3

the intensity
chnage in dipole moment

Question 4

stretching of a polar group causes a (small/large) chnaange in dipole moment of the molecule

Answer 4

Large

Question 5

stretching of a nonpolar group causes a (small/large/no change) chnaange in dipole moment of the molecule

Answer 5

no change

Question 6

It characterizes C=O stretching vibration

Answer 6

Intense IR absorption or minimum transmittance

Question 7

The amount of energy (or frequency of radiation) required to excite a particular bond depends upon: (3)

Answer 7

(1) strength of the bond
(2) mass of the atoms
(3) spatial arrangement of the atoms in the bond/functional group

Question 8

the amount of energy required to excite a particular bond (decreases/increases) with decreasing bond order (bond strength) and (increases/decreases) with increasing mass.

Answer 8

decreases
decreases

Question 9

arrange in decreasing order according to their frequency of absorption as a result of mass differences: C-Br, C-F, C-Cl

Answer 9

C-F > C-Cl > C-Br

Question 10

Infrared spectoscopy is very useful in: (2)

Answer 10

(1) elucidating structures of unknown compounds
(2) the identification of known compounds

Question 11

what can be determined from an IR spectrum

Answer 11

the functional group present in an unknown sample

Question 12

it is a record of the absorption which because of very closely spaced unresolved lines appear as bands.

Answer 12

IR spectrum

Question 13

sepctra are often presented with the _______ representing frequency and the _______ representing percentage transmission

Answer 13

abscissa
ordinate

Question 14

equation for solving percentage transmission

Answer 14

T = I/Io x 100

Question 15

at what frequncy us the fingerprint region

Answer 15

(1550-650) cm-1

Question 16

if 2 samples give identical bands including those of the fingerprint region, then the two samples are

Answer 16

identical

Question 17

an instrument that directs photons of varying wavelengths into the sample being studied

Answer 17

spectrophotometer

Question 18

It senses and records the percentage of photons absorbed

Answer 18

spectrophotometer

Question 19

The __________ directs photons of IR radiation into the sample

Answer 19

IR spectrophotometer

Question 20

In this experiment what instrument (spectrophotometer) will be used?

Answer 20

Nicolet IS5 Thermoscientific FT-IT

Question 21

objective(s) of the experiment

Answer 21

to learn and practice interpreting the spectra of different compounds

Question 22

PROCEDURE:
For Solid sample

Answer 22

place a small amount of the solid onto the solid sample holder. Run the spectrum

Question 23

PROCEDURE:
For Liquid Sample

Answer 23

Place 1 drop of the liquid onto the NaCl cell. Place gently over the other cell. Reassemble the plates and place it in the sample compartment Run the spectrum. Clean the cells w/ acetone