CHM260 Tutorial Questions Chptr 2: MOLECULAR ABSORPTION SPECTRO

Name the suitable cell materials for use in the following electromagnetic region: a) UV b) Visible

Answer explanation

a) LiF / Fused silica / quartz

b) LiF / Fused silica / quartz / corex glass / silicate glass

Define the term 'continuum source' and give one (1) example of this source.

Answer explanation

Source which provides a broad distribution of wavelength within a particular spectral range. Example: D2 lamp / Nerst glower / arc lamp / tungsten lamp

Name the type of detector commonly used in UV-Visible spectroscopy.

Answer explanation

Phototubes/ photomultiplier tubes (PMT)

Draw the block diagram of a double beam spectrophotometer and label each component.

Answer explanation

(refer notes)

In spectroscopic analysis: a) name one (1) suitable cell material for use in UV spectroscopy. b) give an example of a continuum source for infrared (IR) spectroscopy. c) state the principle of use for a quantum detector. d) what is the function of a monochromator or a filter?

Answer explanation

a) LiF / Fused silica / quartz

b) Nerst glower / tungsten lamp

c) Quantum detector is based on the photoelectric effects, where photoelectrons are ejected from a photopositive surface by electromagnetic radiation. The photoelectrons are attracted to the anode, resulting in photocurrent which can be amplified and measured.

d) To restrict the radiation being measured to a narrow band that is absorbed or emitted by an analyte

State one (1) advantage of a double-beam instrument compared to a single-beam instrument.

Answer explanation

Compensate the most short-term fluctuations in the radiant output of the source OR Compensate for wide variations of source intensity with wavelength OR Well suited for continuous recording of the absorption spectra

Define the term 'chromophores'.

Answer explanation

Unsaturated organic functional groups that absorb in UV/Vis region