Question 1

For which application is powder X-ray diffraction not suitable for?&#10;A) phase transitions&#10;B) chemical composition&#10;C) sample purity

Accepted Answer

Powder X-ray diffraction (XRD) is a powerful technique primarily used for identifying crystalline phases and analyzing phase transitions and sample purity. However, it is not directly used for determining the chemical composition of a sample. Techniques such as X-ray fluorescence (XRF) or mass spectrometry are more suitable for identifying and quantifying the elemental composition of a sample.

Question 2

Why does neutron diffraction require larger crystal size than single crystal X-ray diffraction?&#10;A) Neutrons do not interact well with charged particles.&#10;B) Neutron sources have lower flux than X-ray sources.&#10;C) Larger sample shortens the time of the experiment.

Accepted Answer

Neutron sources have lower flux compared to X-ray sources, meaning fewer neutrons are available to interact with the sample. This necessitates a larger crystal size to ensure sufficient interaction for a detectable diffraction pattern.

Question 3

What type of information can be obtained from ultraviolet-visible spectroscopy?
(i) electronic structure
(ii) concentration of absorbing species
(iii) chemical composition

A) All of them
B) (ii) and (iii)
C) (i) and (ii)

C

Accepted Answer

Ultraviolet-visible spectroscopy primarily provides information about the electronic structure of molecules and the concentration of absorbing species. It does not directly give detailed chemical composition.

Question 4

Find the correct statement on the infrared spectroscopy: A) The samples are diluted with solid, dry KBr and pressed into a pallet. B) Typical infrared instrument has a range between 400 and 24 cm^-1. C) The infrared spectrometers use strong laser radiation.

Accepted Answer

Infrared spectroscopy often involves preparing samples by diluting them with solid, dry potassium bromide (KBr) and pressing the mixture into a pellet. This method is used because KBr is transparent to infrared radiation, allowing the IR light to pass through the sample without being absorbed by the KBr itself.

Question 5

Which of the listed compounds would be best suited for the EPR analysis? A) Group 1 halides B) A complex containing Ti³⁺ C) Organic materials

Accepted Answer

EPR (Electron Paramagnetic Resonance) analysis is best suited for materials with unpaired electrons. The complex containing Ti³⁺ implies the presence of unpaired electrons due to the transition metals and their oxidation states, making it suitable for EPR analysis. Group 1 halides and organic materials typically do not have unpaired electrons unless they are specifically radicals or have paramagnetic impurities.

Question 6

What is the purpose of a standard in NMR spectroscopy?&#10;A) To set the reference point for peak intensity.&#10;B) To help determine an unknown concentration.&#10;C) To set the zero on the chemical shift scale.

Accepted Answer

The purpose of a standard in NMR spectroscopy is to set the zero on the chemical shift scale, which is typically done using tetramethylsilane (TMS) as the standard reference compound.

Question 7

What is mass spectrometry used for?&#10;A) To detect the masses of molecules and their fragments.&#10;B) To detect the concentration of a molecular analyte in a sample.&#10;C) To detect the structure of a molecule.

Accepted Answer

Mass spectrometry is primarily used to determine the masses of molecules and their fragments, which can help infer molecular structure and composition.

Question 8

What do atomic absorption spectroscopy, CHN analysis and X-ray fluorescence analysis have in common?&#10;A) They are all based on absorption of radiation.&#10;B) They are all used to analyse chemical composition.&#10;C) They are all used in structural analysis.

Accepted Answer

Atomic absorption spectroscopy, CHN analysis (for Carbon, Hydrogen, Nitrogen), and X-ray fluorescence analysis are all analytical techniques used to determine the chemical composition of a sample, rather than its structure.

Question 9

A new complex containing Cu²⁺ is prepared. Which method would you use to (i) determine bond lengths in the complex and (ii) check its chemical formula? A) Infrared spectroscopy for (i) and mass spectroscopy for (ii). B) Single crystal X-ray diffraction for (i) and CHN analysis for (ii). C) EPR for (i) and thermal analysis for (ii).

Accepted Answer

Single crystal X-ray diffraction is used to determine the precise arrangement of atoms in a crystalline solid, including bond lengths, while CHN analysis is a method for determining the chemical formula of a compound by measuring the percentages of carbon, hydrogen, and nitrogen it contains.

Question 10

Which technique(s) do not involve use of any radiation?
(i) Mossbauer spectroscopy
(ii) cyclic voltammetry
(iii) electron paramagnetic resonance
(iv) CHN analysis

A) (ii) and (iv)
B) (i) and (iii)
C) (iii) and (iv)

Accepted Answer

Cyclic voltammetry and CHN analysis do not involve the use of radiation. Cyclic voltammetry is an electrochemical technique, while CHN analysis involves combustion to measure carbon, hydrogen, and nitrogen content in a sample.

Deck 8: Physical Techniques in Inorganic Chemistry