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OrgChem Lab (2nd sem) > Activity No. 4 > Flashcards

Activity No. 4 Flashcards

1
Q

an obvious difference between certain compounds

A

color

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2
Q

color of quinone

A

yellow

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3
Q

color of chlorophyll

A

green

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4
Q

their color range from bright yellow to deep red, depending on double bond conjugation

A

2,4-dinitrophenylhydrazone derivatives of aldehydes and ketones

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5
Q

color of aspirin

A

colorless

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6
Q

although we see sunlight(or white light) as _____________ in color, it is actually composed of a broad range of ____________

A

radiatiom wavelengths in the ultraviolet (UV), visible and infrared (IR) portions of the spectrum

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7
Q

the component colors of the visible portion can be separated by ________

A

passing sunlight thru a prism

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8
Q

what is the function of a prism

A

acts to bend the light in differing degrees according wavelength

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9
Q

visible wavelengths cover a range from

A

400-800 nm

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10
Q

color that has the longest visible wavelength

A

red

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11
Q

color that has the shortest visible wavelength

A

voilet

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12
Q

order of decreasing wavelength

A

ROY G BIV

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13
Q

which has high frequency, UV or IR?

A

UV

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14
Q

WAVELENGTH IN nm:
RED

A

620-780 nm

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15
Q

WAVELENGTH IN nm:
ORANGE

A

585-620 nm

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16
Q

WAVELENGTH IN nm:
YELLOW

A

570-585 nm

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17
Q

WAVELENGTH IN nm:
GREEN

A

490-570 nm

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18
Q

WAVELENGTH IN nm:
BLUE

A

440-490 nm

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19
Q

WAVELENGTH IN nm:
INDIGO

A

420-440 nm

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20
Q

WAVELENGTH IN nm:
VIOLET

A

400-420 nm

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21
Q

absorption of UV radiation causes ________

A

the valence electrons in the molecules to go the higher (anti-bonding) energy levels

22
Q

what electronic excitations can occur in a spectral range of 200-400 nm

A

n —> π*
π —> π*
n —> σ*

23
Q

below 200 nm is the

A

far ultraviolet region

24
Q

far ultraviolet region can allow

A

higher energy types of electronic excitation

25
Q

TRUE/FALSE.
Oxygen can still absorb radiation from the far UV region and will therefore be an obstacle in getting reliable results

A

TRUE

26
Q

this region is located beyond 400 nm

A

Visible region

27
Q

visible region can cause

A

π —> π* electronic transition in colored polyunsaturated conjugated compounds

28
Q

data gatgered from uv-vis spectroscopy are useful in: (2)

A

(1) in structure elucidation chemical analysis
(2) in qunatitative analysis

29
Q

these two provide information to the general chemical structure

A

(1) wavelength of maximum absorption ( π*max)
(2) intensity or molar absorptivity, ϵ

30
Q

trend in energy required for the different electronic transitions is :

A

n—π* < π—π* < n—σ*

31
Q

conjugated double bond systems require (more/less) energy or (longer/shorter) πmax than __________ for π—π transitions

A

less
longer
nonnon-conjugated system

32
Q

as the number of π molecular orbitals (increases/decreases), distance between π and π* molecular orbitals (increase/decrease)

A

increases
decreases

33
Q

only what electronic transition occur with high intensity or molar absorptivity (10000-20000)

A

π—π*

34
Q

ϵ for ______ transitions are very small (10-100), which means there are infrequent transitions due to geometrical difficulties

A

n—π*

35
Q

is a specific value for a particular compound

A

molar absorptivity

36
Q

equation of Beer’s law

A

A= log Io/I = ϵbc

where: A= absorbance (optical density)
Io= intensity of incident light
I= intensity of light transmitted by sample
ϵ= molar absorption coefficient
b= thickness of sample in cm
c= concentratiom of solution in M

37
Q

what instrument will be used to determine the absorbance of acetone, salicylic acid and various dyes versus water solvent as blank

A

double-beam Lasany UV-Vis spectrophotometer Model LI-2800

38
Q

the solvent used to dissolve the samples

A

distilled water

39
Q

other solvents that are transparent at UV which can also be used but these must be of spectral grade

A

hexane, 95% ethyl alcohol, etc

40
Q

solvents must be __________ and _______ since a very small amount of substance as on a fingerprint can give a spectrum

A

very clean
pure

41
Q

these ions absorb UV

A

Dissolved ions such as nitrates and iodides

42
Q

these ions absorb visible radiation

A

colored ions such as Fe+3

43
Q

Sample cells for UV must be made of

A

fused quartz

44
Q

why does the sample cell for UV must not be made of silica (glass)?

A

since silica(glass) absorb ultraviolet radiation

45
Q

thickness of the sample cell

A

10 mm

46
Q

objective of the experiment

A

to learn how to use the uv-vis spectrophotometer and the data obtained herein for structure elucidation

47
Q

PREPARATION OF SOLUTIONS:
step 1. From thr Merck Index, obtain the0. _______ and ______ of ________, ______, amd the three ______. Prepare _________ of acetone (___g/___mL) and ________(0.1g/100mL). This will serve as the _______ for the entire class

A

Molecular weight
density
acetone
salicylic acid
dyes
aqueous solutions
0.15g/100 mL
salicylic acid
stock solution

48
Q

PREPARATION OF SOLUTIONS:
Step 2

A

Pipette 3 mL of this solution into another 100 mL graduated cylinder and dilute to mark

49
Q

PREPARATION OF SOLUTIONS:
Step 3

A

Prepare 2.0 x 10^-6 M solutions (in 10 mL volumetric flasks) of each dye using water as solvent

50
Q

SAMPLE CELLS AND ABSORPTION MEASUREMENTS:
Step 1

A

The clear faces of the cuvettes must not be touched. Rinse the 2 cuvettes or sample cells w/ distilled water, then with ethanol

51
Q

SAMPLE CELLS AND ABSORPTION MEASUREMENTS:
Step 2

A

Dry. Rinse one cuvette w/distilled water and the other w/solution. Then, refill them about 2/3 full, with their respective liquids. Cover. Make sure there are no air bubbles. Wipe the clear faces of the cuvettes

52
Q

SAMPLE CELLS AND ABSORPTION MEASUREMENTS:
Step 3

A

Plug the instrument to 220v outlet. Allow 30-minute warm-up. Obtain the absorption spectrum of each sample solution from 200-800 nm

OrgChem Lab (2nd sem) (9 decks)

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