This set of Solid State Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Applications of DTA and TGA”.
1. Which of the following option is appropriate for the TGA and DTA?
a) TGA and DTA measures only weight
b) TGA measures only weight while DTA measures other effects
c) TGA and DTA measures only temperature
d) TGA measures only temperature while DTA measures other effects
Explanation: DTA is more versatile than TGA, TGA detects effects which involve weight changes only. DTA also detects such effects in addition, detects other effects such as polymorphic transitions, which do not involve changes in weight.
2. In the schematic DTA sequence having reversible and irreversible changes, starting with the hydrated material, which of the following steps occurs first on heating?
Explanation: During the DTA, differential thermal analysis sequence having reversible and irreversible changes when started with hydrated material, dehydration is the first step that occurs on heating and appears as an endotherm On cooling, the melt crystallizes and the polymeric change also occur, exothermically on cooling but rehydration does not occur.
3. On studying the reversible process during DTA which of the following is observed on both heating and cooling?
Explanation: On both heating and cooling during the studies of reversible processes in DTA, differential thermal analysis, it is common to observe hysteresis, for instance, the exotherm that appears on cooling may be displaced to occur at a lower temperature than the corresponding endotherm which appears on heating.
4. Which one of the following options is not true for hysteresis?
a) It depends on the nature of the material
b) It depends on the structural change involved
c) It doesn’t depend on the experimental conditions
d) It doesn’t depend on the concentration of the electrode
Explanation: Hysteresis depends not only on the nature of the material and the structural changes involved such as difficult transitions involving, for example, the breaking of string bonds are likely to exhibit much hysteresis but also on the experimental conditions such as the rates of heating and cooling.
5. In the application of DTA and DSC which of the following parameters is measured for the glasses?
a) Concentration of the glass
b) Solubility of the glass
c) Cooling temperature
d) Transition temperature
Explanation: In the application of DTA and DSC for glass the transition temperature Tg is measured. This appears not as a clear peak but rather as a broad anomaly in the baseline of the DTA curve, and it represents the temperature at which the glass transforms from a rigid solid to a supercooled, albeit very viscous, liquid.
6. IN refractories, transitions such as α⇄β quartz or quartz ⇄ cristobalite have which of the following effect?
a) Nasser’s effect
b) Crystal effect
c) Dislocation effect
d) Deleterious effect
Explanation: During the, transitions such as α⇄β quartz or quartz ⇄ cristobalite, deleterious effect is observed on silica refractories because volume changes associated with each transition reduce the mechanical strength of the refractory. These transitions, which should be prevented from occurring if possible, may be monitored by DTA (differential thermal analysis).
7. DTA can be used for which of the following process?
a) Line positions of the crystals
b) Mechanical properties of the crystals
c) Phase diagrams
d) Catalytic properties of enzymes
Explanation: Differential thermal analysis is a powerful method for the determination of phase diagram, especially when used in conjunction with other techniques such as X-ray diffraction for the identification of the crystalline phases present.
8. For the decomposition of the anhydrous calcium oxalate, which of the following steps occur?
a) Intermediates, transition state, product
b) Intermediates, anhydrous oxalate, calcium oxysalts
c) Intermediates, aqueous hydrates, calcium hydroxides
d) Intermediates, anhydrous calcium oxalate, calcium carbonate
Explanation: In the multistage decomposition processes, TG either alone or in conjunction with DTA may be used to separate and determine the individual steps. A known example is the decomposition of the anhydrous calcium oxalate where the decomposition occurs in three steps, intermediates, anhydrous calcium oxalate, and calcium carbonate.
9. A rapid TGA method is used for which of the following process?
a) Decomposition of polymers exothermally
b) Decomposition of enzymes exothermally
c) Decomposition of crystals endothermally
d) Decomposition of reactions isothermally
Explanation: An accurate and rapid TGA method is to study the decomposition of reactions isothermally, the TGA furnace is arranged at a pre-set temperature and the sample introduced directly at this temperature. After allowing 2 to 3 minutes for the sample with time can be followed. The process may be repeated at other temperatures and the results analyzed to determine reaction mechanisms, etc.
10. Which of the following parameters can be used, using the DSC and DTA cells?
a) Catalytic properties of enzyme
b) Elasticity of crystals
c) Enthalpy of substances
d) Line positions of phases
Explanation: With DSC cells or with DTA cells that have been designed for a calorimetric response such measurements may be made rather more accurately and in addition the heat capacity of substances or phases may be measured as a function of temperature.
Sanfoundry Global Education & Learning Series – Solid State Chemistry.
To practice all areas of Solid State Chemistry, here is complete set of 1000+ Multiple Choice Questions and Answers.