Spectroscopy

Q1: Molar absorbtivity is the measure of the

A amount of light absorbed per unit length

B amount of light absorbed per unit concentration

C amount of light reflected and absorbed per unit concentration

D None of the above

ANS:B - amount of light absorbed per unit concentration

Molar absorptivity =A/CL.

Molar absorptivity is depended upon path length, then why the answer is B?

Q2: Vibrational spectroscopy is

A a large mass on a weak spring

B a flashlight through a prism and shake it

C a class of spectroscopic techniques which analyzes molecular motions

D an Infrared spectroscopy

ANS:C - a class of spectroscopic techniques which analyzes molecular motions

No answer description is available.

Q3: Which of the following will oscillate the fastest?

A A large mass on a weak spring

B A large mass on a stiff spring

C A small mass on a stiff spring

D A small mass on a weak spring

ANS:C - A small mass on a stiff spring

No answer description is available.

Q4: Molar absorbtivities of compounds exhibiting charge transfer absorption are

A small

B moderate

C large

D none of these

ANS:C - large

Species that exhibit charge-transfer absorption are of particular importance because their molar absorptivities are very large (max > 10,000). Thus, these complexes provide a highly sensitive means for detecting and determining absorbing species. Complexes exhibit charge transfer absorption are called charge-transfer complexes. In order for a complex to exhibit a charge-transfer spectrum, it is necessary for one of its components to have electron-donor characteristics and for the other component to have electron-acceptor properties. Absorption of radiation then involves the transfer of an electron from the donor to an orbital that is largely associated with the acceptor.

Q5: In the equation, A = ε bc, what quantity is represented by "ε"?

A Absorbtivity

B Molar absorbtivity

C Path length

D None of these

ANS:B - Molar absorbtivity

A is Absorbance or optical density or extinction coefficient.
C is concentration.
T pathlength.

Q6: Beer's Law states that

A absorbance is proportional to both the path length and concentration of the absorbing species

B absorbance is proportional to the log of the concentration of the absorbing species

C absorbance is equal to P0 / P

D none of the above

ANS:A - absorbance is proportional to both the path length and concentration of the absorbing species

Beer's law resulted to the concentration of absorbing species.

Lambert's law related to thickness/pathlength of absorbing species.

Q7: Why must the voltage supplied to a tungsten lamp be very stable?

A Because if it wasn't, the lamp would bum out

B Because amount of energy the lamp emits is proportional to the fourth power of the operating voltage

C Because the lamp will only function at a specific voltage

D All of the above

ANS:B - Because amount of energy the lamp emits is proportional to the fourth power of the operating voltage

No answer description is available.

Q8: A simple harmonic oscillator may absorb energy

A at anytime.

B when the frequencies match exactly

C when the amplitudes are the same.

D at no time.

ANS:B - when the frequencies match exactly

When there is a match of frequency, energy is been absorb.

Q9: Where does a carbonyl (C=0) stretch appear in an IR spectrum?

A 1740-1720

B 1870-1650

C 3640-3250

D 160-110

ANS:B - 1870-1650

Please explain the given answer.

Q10: Why is it generally preferable to use absorbance as a measure of absorption rather than % transmittance?

A Because %T cannot be measured as accurately as absorbance

B Because %T is dependant on the power of the incident radiation

C Because absorbance is proportional to the concentration of the analyte, whereas %T is not

D none of the above

ANS:C - Because absorbance is proportional to the concentration of the analyte, whereas %T is not

No answer description is available.

Q11: Which of the following components of a monochromator is the dispersing element?

A The collimating lens

B The entrance slit

C The diffraction grating

D None of these

ANS:C - The diffraction grating

No answer description is available.

Q12: Which of the following relationships between absorbance and %transmittance is incorrect?

A A = log10 100 / %T

B A = 2 - log10 %T

C A = log10 1 / T

D All are correct

ANS:C - A = log10 1 / T

I think the correct answer is D]. All are correct.

Q13: Which of the following is not an IR vibrational mode?

A Stretching

B Scissoring

C Rocking

D Rolling

ANS:D - Rolling

No answer description is available.

Q14: Why are rotational transitions of little use to a spectroscopist?

A Because the energy required to induce a rotational transition is so small that it cannot be measured

B Because rotational transitions are extremely rare

C Because, in liquids and solids, spectral lines corresponding to rotational transitions are broadened as the result of molecular collisions and other interactions

D All of the above

ANS:C - Because, in liquids and solids, spectral lines corresponding to rotational transitions are broadened as the result of molecular collisions and other interactions

Explain the answer.

Q15: In the past, IR spectra had to be aquired one wavelength at a time, which took a long time. Today quick spectra is due to the

A the Fourier Transfer Algorithm allows us to scan all frequencies at once

B light is faster today that it used to be

C absence of broad spectrum of wavelenth

D none of the above

ANS:A - the Fourier Transfer Algorithm allows us to scan all frequencies at once

No answer description is available.

Q16: UV-Vis spectroscopy of organic compounds is usually concerned with which electronic transition(s)?

A σ → σ*

B n → σ*

C n → π* and π → π*

D none of these

ANS:C - n → π* and π → π*

Non bonded electrons to σ* transitions are considered too? Explain, please.



img not found
img

For help Students Orientation
Mcqs Questions

One stop destination for examination, preparation, recruitment, and more. Specially designed online test to solve all your preparation worries. Go wherever you want to and practice whenever you want, using the online test platform.