post lab discussion: exp. 10

Question 1

it deals with the production, measurement and interpretation of spectra arising from the interaction of electromagnetic radiation with matter

Answer 1

spectroscopy

Question 2

spectroscopy utilizing radiation in the UV-Vis range

Answer 2

UV-Vis Spectroscopy

Question 3

what is the range wavelength of electromagnetic radiation in the UV–Vis portion of the spectrum

Answer 3

200 to 700 nm

Question 4

UV range -
Vis range -

Answer 4

UV range - 200 to 350 nm
Vis range - 350nm to 700 nm

Question 5

true or false:
the UV range is colorless to the human eye

Answer 5

true

Question 6

true or false:
different wavelengths in the visible range does not have a characteristic color

Answer 6

false - they each have a characteristic color

Question 7

what are the 2 general categories based on the type of radiation-matter interaction that the UV-Vis spectroscopy is divided to

Answer 7

absorbance
fluorescence

Question 8

it is to determine the concentration analyte in a given solution

Answer 8

quantitative absorption spectroscopy

Question 9

wavelength color:
less than 380 -
more than 780 -

Answer 9

less than 380 - ultraviolet (violet)
more than 780 - near infrared (purple)

Question 10

the wheel color

Answer 10

R
O
Y
G
B
V

Question 11

it is fast, simple and inexpensive method to determine the concentration of an analyte in solution, where the type of compound to be analyzed (‘analyte’) is known

Answer 11

UV-Vis analysis

Question 12

what equipment can we use to analyze with UV-Vis analysis?

Answer 12

spectrophotometer

Question 13

I0 =
I =

Answer 13

I0 = radiation coming in,
I = radiation coming out

decrease of a beam of radiation as it passes through a cuvette containing an absorbing solution

Question 14

briefly explain what happens in the spectrophotometer machine

Answer 14

sample-holding cell or cuvette containing the solution to be analyzed is placed in the path of radiation of a selected wavelength

amount of radiation passing through the sample is measured relative to a reference sample

relative amount of light passing through the sample is then used to determine the concentration of the analyte (the substance being measured) in the solution

decrease in radiation intensity after passing through the solution is due to the absorption of photons by the absorbing species present in the solution

Question 15

explain the difference between transmittance and absorbance

Answer 15

transmittance - fraction of the
incident light absorbed by the solution, defined as the ratio of I to I0.

T = I/I0
it can also be expressed as percentage: %T = (I/I0) × 100

absorbance - measure of the amount of light absorbed.

A = log(I0/I) = − logT = 2− log %T

Question 16

according to ______ the absorbance is proportional to the concentration of the substance in solution

Answer 16

Beer’s Law
A = εcl

c = concentration of solution (M)
l = optical path length, i.e. dimension of the cuvette (cm)
e = molar absorptivity (L/mol·cm), which is constant for a particular substance at a particular wavelength; ↑ ε, ↑ amt. of radiation absorbed

Question 17

it is the peak that represents the wavelength of maximum absorption

Answer 17

“lambda-max” (λmax)

Question 17

the linearity of the Beer-Lambert law is limited by

Answer 17

chemical and instrumental factors

Question 18

what are the 2 key advantages of taking measurements at this lambda-max peak

Answer 18

maximum sensitivity:
absorbance per unit change in analyte concentration, meaning measurements at the peak are most sensitive to concentration changes

greater adherence to beer’s law:
peak wavelength region, the radiation beam consists of wavelengths with relatively small differences in their molar absorptivities for the analyte being measured

Question 19

when drawing calibration curve,
y axis:
x axis:

it is to determine?

Answer 19

y axis: absorbance
x axis: concentrations

determine the concentration of unknown sample solution by measuring its absorbance

Question 20

what happens when the salicylate ions can be derived with Fe (III)

Answer 20

produce a violet colored complex
that can be quantified at its absorption maxima of 530nm