Question 1

Which component in a UV/Vis spectrophotometer is responsible for isolating a specific analytical wavelength ($$\lambda_{anal}) $$from the rest of the spectrum?

Accepted Answer

Monochromator

Question 2

A compound absorbs light at 430 nm with a molar absorptivity ($$\varepsilon) of$$ $$5.12 	imes 10^3$ L·cm$$^{-1}$$·mol$$^{-1}$$. If the concentration (c$) is 3.80$$ 	imes $$10^{-5} M $$and the pathlength ($$l) is 1 cm$$, what is the absorbance ($$A) $$according to Beer-Lambert Law?

Accepted Answer

$$A = 0.194$$

Question 3

Which of the following is a limitation of UV/Vis spectrophotometry when analyzing complex samples?

Accepted Answer

Analytical wavelengths can overlap, causing interference

Question 4

What is the main function of a photomultiplier tube in a spectrophotometer?

Accepted Answer

To convert incident light into an electrical signal

Question 5

Which region of the electromagnetic spectrum is used to analyze colourless compounds in UV/Vis spectrophotometry?

Accepted Answer

UV region (200–400 nm)

Question 6

A solution has a transmittance ($$T) of 25.4$$%. What is its absorbance ($$A$$)?

Accepted Answer

$$A = 0.595$$

Question 7

Which of the following is a strength of atomic absorption spectroscopy (AAS) compared to flame emission spectroscopy (FES)?

Accepted Answer

AAS is more sensitive due to greater concentration of electrons in the ground state

Question 8

What is the purpose of adding strontium chloride (SrCl$$_2) or $$lanthanum chloride (LaCl$$_3) $$during AAS or FES analysis?

Accepted Answer

To remove anionic interference by precipitating out SO$$_4$$^{2-}$$ and PO$$_$$4^{3-}$$

Question 9

Which sample cell material is suitable for measurements in the UV region (200–380 nm)?

Accepted Answer

Quartz

Question 10

In ICP-OES, what is the main advantage of using a polychromator and diode array detector?

Accepted Answer

It allows simultaneous detection of multiple elements at different wavelengths

Question 11

Which interference in AAS and FES is caused by high flame temperatures leading to atom ionization and loss of excited electrons?

Accepted Answer

Ionization interference

Question 12

A calibration curve for vanillin in a cool drink shows a sample absorbance of 0.180. If the diluted concentration is 34 ppm and the dilution factor is 10, what is the original concentration in ppm?

Accepted Answer

340 ppm

Question 13

Which of the following is NOT a typical application of UV/Vis spectrophotometry?

Accepted Answer

Quantifying alkali metals in biological fluids

Question 14

What is the relationship between absorbance ($$A) $$and transmittance ($$T) in $$spectrophotometry?

Accepted Answer

$$A = -\log T$$

Question 15

Which sample introduction method is used in AAS and FES to convert liquid samples into an aerosol for analysis?

Accepted Answer

Nebulizer

Question 16

Which of the following is a limitation of ICP-OES?

Accepted Answer

It requires skilled technicians for operation and maintenance

Question 17

Which type of interference in AAS and FES can be solved by adjusting the viscosity of the sample using ethanol or glycerol?

Accepted Answer

Viscosity interference

Question 18

What is the main principle behind atomic absorption spectroscopy (AAS)?

Accepted Answer

Atoms absorb element-specific radiation from a hollow cathode lamp

Question 19

Which of the following is a strength of UV/Vis spectrophotometry?

Accepted Answer

It is non-destructive and allows analyte recovery

Question 20

In flame emission spectroscopy (FES), which group of elements is most commonly analyzed?

Accepted Answer

Alkali and alkaline earth metals

Spectroscopy Techniques in Analytical Chemistry: UV/Vis, AAS, FES, and ICP-OES

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