Questions and answers for exam Preparation

MCQs

Total Questions : 147 | Page 3 of 15 pages

Question 21. Beer's Law states that

absorbance is proportional to both the path length and concentration of the absorbing species
absorbance is proportional to the log of the concentration of the absorbing species
absorbance is equal to P0 / P
none of the above

Discuss Question

Answer: Option A. -> absorbance is proportional to both the path length and concentration of the absorbing species
Answer: (a).absorbance is proportional to both the path length and concentration of the absorbing species

Question 22. Molar absorbtivities of compounds exhibiting charge transfer absorption are

small
moderate
large
none of these

Discuss Question

Answer: Option C. -> large
Answer: (c).large

Question 23. Why is it generally preferable to use absorbance as a measure of absorption rather than % transmittance?

Because %T cannot be measured as accurately as absorbance
Because %T is dependant on the power of the incident radiation
Because absorbance is proportional to the concentration of the analyte, whereas %T is not
none of the above

Discuss Question

Answer: Option C. -> Because absorbance is proportional to the concentration of the analyte, whereas %T is not
Answer: (c).Because absorbance is proportional to the concentration of the analyte, whereas %T is not

Question 24. Molar absorbtivity is the measure of the

amount of light absorbed per unit length
amount of light absorbed per unit concentration
amount of light reflected and absorbed per unit concentration
None of the above

Discuss Question

Answer: Option B. -> amount of light absorbed per unit concentration
Answer: (b).amount of light absorbed per unit concentration

Question 25. Which of the following relationships between absorbance and %transmittance is incorrect?

A = log10 100 / %T
A = 2 - log10 %T
A = log10 1 / T
All are correct

Discuss Question

Answer: Option C. -> A = log10 1 / T
Answer: (c).A = log10 1 / T

Question 26. What is the relationship between wavelength and wave number?

Wavenumber = 1 / wavelength in centimeters
Wavenumber - wavelength in nanometers = 1
Wavelength in nanometers x wavenumber = 1
None of the above

Discuss Question

Answer: Option A. -> Wavenumber = 1 / wavelength in centimeters
Answer: (a).Wavenumber = 1 / wavelength in centimeters

Question 27. Where does a carbonyl (C=0) stretch appear in an IR spectrum?

1740-1720
1870-1650
3640-3250
160-110

Discuss Question

Answer: Option B. -> 1870-1650
Answer: (b).1870-1650

Question 28. Why do fluorescence spectrometers often use double-beam optics?

So a reference solution can be used
To compensate for beam attenuation by the monochromator
To compensate for power fluctuations in the radiation source
All of the above

Discuss Question

Answer: Option C. -> To compensate for power fluctuations in the radiation source
Answer: (c).To compensate for power fluctuations in the radiation source

Question 29. In the intersystem crossing

the spin of an excited electron reverses, changing the state of the molecule (from singlet state to triplet state or vice versa)
a molecule converts its excess energy to light, and emits a photon
a molecule converts excess electronic energy to vibrational energy
all of the above

Discuss Question

Answer: Option A. -> the spin of an excited electron reverses, changing the state of the molecule (from singlet state to triplet state or vice versa)
Answer: (a).the spin of an excited electron reverses, changing the state of the molecule (from singlet state to triplet state or vice versa)

Question 30. Why must the radiation source for fluorescence spectrometry be more powerful than for absorption spectroscopy?

Because the magnitude of the output signal is proportional to the power of the incident radiation
Because the sample won't fluoresce if the incident radiation is of low power
To allow for scattering by the sample
None of the above

Discuss Question

Answer: Option A. -> Because the magnitude of the output signal is proportional to the power of the incident radiation
Answer: (a).Because the magnitude of the output signal is proportional to the power of the incident radiation