Spectroscopy Calculations & Pipetting

Question 1

Pipetting Accuracy

Answer 1

1. weigh an empty weigh boat (record the weight) or tare/zero the balance with the weigh boat on it
2. use the pipette to add 1000uL of the solution to the tube
3. Record the new weight
4. Repeat this procedure for 5 times and calculate the average and standard deviation
5. Repeat steps 1 to 4 for 200uL and 500uL ( if available)
   Record all results and calculate the average and standard deviation of each set

Question 2

m = milli

Answer 2

1 x 10-3

Question 3

u = micro

Answer 3

1 x 10-6

Question 4

n = nano

Answer 4

1 x 10-9

Question 5

p = pico

Answer 5

1 x 10-12

Question 6

k = kilo

Answer 6

1 x 10-3

Question 7

molarity =

Answer 7

Grams/Litre /Molecular Mass

Question 8

Molecular Mass

Answer 8

is sometimes written as Daltons (Da) or Atomic Mass Units (AMU),

Question 9

stock solutions

Answer 9

are reagents that are generally made up at high concentrations

Question 10

C1 V1 = C2 V2

Answer 10

C1 = Stock Concentration
V1 = Stock Volume
C2 =Dilution Concentration
V2 = Dilution Volume

Question 11

sunlight (or white light) uniform or homogenous in color?

Answer 11

Actually composed of a broad range of radiation wavelengths in the ultraviolet (UV), visible and infrared (IR) portions of the spectrum

Question 12

Prism

Answer 12

acts to bend the light in differing degrees according to wavelength

Question 13

Lycopene

Answer 13

red pigment (in tomatoes)

Question 14

Lutein

Answer 14

a yellow pigment ( in egg yolks)

Question 15

b-carotene

Answer 15

an orange pigment ( in carrots)

Question 16

A Chromophore

Answer 16

is the part of a molecule that absorbs or reflects light. Chromophores determine the color of a molecule

Question 17

UV transparent

Answer 17

is the term used for molecules with no double bonds or only one double bond as they dont absorb in the UV-VIS region eg. any alkane

Question 18

A Spectrophotometer

Answer 18

records wavelengths at which absorption occurs + the degree of absorption at each wavelength

Question 19

monochromatic

Answer 19

a single wavelength

Question 20

cuvette

Answer 20

transparent container

Question 21

I = I o

Answer 21

the sample compound does not absorb light of a given wavelength

Question 22

I<I o

Answer 22

the sample compound absorbs light at a given wavelength

Question 23

I o =

Answer 23

intensity of the reference beam
incident light

Question 24

I =

Answer 24

transmitted light

Question 25

absorbance =

Answer 25

= log Io / I
Absorbance is also referred to as the Optical Density (OD)

Question 26

intensely absorbing compounds

Answer 26

must be examined in dilute solution !
this is because the absorbance of a sample will be proportional to its molar concentration in the sample cuvette

Question 27

different compounds =

Answer 27

= very different absorption maxima and absorbances

Question 28

molar absorptivity

Answer 28

a corrected absorption value, used when comparing the spectra of different compounds

Question 29

molar absorptivity =

Answer 29

= AI c I
where:
A = absorbance
c = sample concentration in moles/liter
I = length of light path through the cuvette in cm