Questions on Instrumental Methods of Analysis

1 1 Questions on Instrumental Methods of Analysis 1. Which one of the following techniques can be used for the detection in a liquid chromatograph? a. Ultraviolet absorbance or refractive index measurement. b. Increase in temperature c. Ionization in flame d. Thermal conductivity Answer = a 2. Considering high performance liquid chromatography , which one of the following statements is FALSE? a. hplc is suitable for the separation and determination of the nonvolatile ( high boiling point) components. b. The stationary phase could be a liquid or a solid. c.

2 Columns longer than 50 meters have been used here to increase the efficiency of separation. d. high pressure is used here to decrease the retention time and improve the separation of components. Answer = c 3. According to Beer s law for a colored solution, which one of the following statements is False? (a) The percent transmission is not directly proportional to the concentration. (b) The absorbance is directly proportional to the concentration. (c) The absorbance does not change when the cell path length (cell thickness) increases.

3 (d) When the concentration of the unknown sample is higher than the highest concentration in the calibration range, the sample should be diluted. Answer = b 4. Deuterium and tungsten lamps are used as a light source in one of the following techniques. (a) Nuclear magnetic resonance spectrophotometers (b) X-rays diffractometers (c) Gas chromatograph (d) Uv/Visible spectrophotometers Answer = d 5. Which one of the following arrangements for the sequence of the main components of a Uv/visible spectrophotometer is Correct? (a) Light source Monochromator Sample cell Detector Readout (b) Light source Detector Sample cell Monochromator Readout (c) Light source Sample cell Detector Monochromator Readout (d) Light source Readout Sample cell Detector Monochromator Answer = a 2 6.

4 Considering the electrochmical cells, which one of the following statements is False? (a) Galvanic cell is that in which a spontaneous chemical reaction takes place and an electrical energy is produced. (b) A nonspontaneous chemical reaction is forced to occur in the electrolysis cell. (c) The salt bridge is used to allow for the movement of electrons from the solution of one half cell to the other (d) The cathode is the electrode at which reduction takes place. Answer = a 7. which one of the following radiation has the longer wavelength a- infra red b- visible c- x-ray d- ultra violet e- gamma rays Answer = a 8.

5 The energy associated with infra red is enough to make a- electronic transitions b- vibrational and rotational transitions c- a full separation of the electron in the outer shell d- X-ray fluorescence e- an electron move from an inner orbital Answer = b 9. The moisture in an organic substance is determined by a- potentiometric titration b- X-ray fluorescence c- X-ray absorption d- Karl Fisher titration e- Measuring the pH of the system Answer = d 10. The technique used to identify a functional group in an organic molecule is a- coulometry b- X-ray fluorescence c- Infrared spectrometry d- Karl Fisher titration e- Conductimetry Answer = c 3 11.

6 One part per million is the same as (a) 1 g/g (b) 1 mg/kg (c) 1 ng/mg (d) All of the above are correct Answer = c 12. Narrow line spectra are emitted by (a) hot solids (b) excited polyatomic molecules (c) molecules in the ground molecular state (d) excited atoms Answer = d 13. What are the dimensions of the molar absorptivity in the Beer's law expression ? (a) Moles per liter (b) Liters per (c) Grams per mole (d) Micrograms per square centimeter Answer = b 14. The region of the electromagnetic spectrum in which the highest energy photons are observed is the (a) ultraviolet (b) infrared (c) microwave (d) x-ray Answer = d 14.

7 An important advantage of a double-beam spectrophotometer over a single-beam spectrophotometer is that (a) it permits cancellation of slow variations of the source power (b) it requires same light source for Uv, Vis, and Infra red radiation (c) it can be used in conjunction with rapid response detection systems (d) a greater range of wavelengths can be used Answer = a 4 15. Grating is a device used in the spectrophotometer to function as (a) a light source (b) a monochromator (c) a detector (d) a nebulizer Answer = b 16.

8 Helium rather than argon, often is used as the carrier gas in GLC when TCD is used as the detector because, (a) He has a higher ionization potential (b) He is more inert (c) He has stable isotopes which separate and cause a change in column behavior. (d) He has a higher thermal conductivity Answer = d 17. To deionize laboratory water by ion-exchange, the best approach employs (a) a column containing a strong acid cation exchanger in the hydrogen form (b) a column containing a strong base anion exchanger in the hydroxyl form (c) a mixed bed column containing a strong acid cation exchanger in the sodium form and a strong base anion exchanger in the hydroxyl form (d)

9 A mixed bed column containing a strong acid cation exchanger in the hydrogen form and a strong base anion exchanger in the hydroxyl form Answer = c 18. Reversed phase hplc is the technique in which (a) stationary phase is solid and mobile phase is liquid . (b) the stationary phase is made of very fine particles. (c) the stationary phase is non polar and the mobile phase is relatively polar. (d) the stationary phase has been silinized with dimethyldichlorosilane. Answer = c 19. Considering high performance liquid chromatography , which one of the Following statements is FALSE?

10 (a) hplc is suitable for the separation and detrmination of the nonvolatile species. (b) The stationary phase used in the hplc column could be relatively polar or nonpolar liquid . (c) The separation efficiency has been increased by decreasing the particle size of the solid support for the stationary phase. (d) Very long columns have been used here to increase the effecirncy of separation. Answer = d 5 20. Considering the electrochmical cells, which on of the following statements is TRUE? a. Electrons move from the cathode towards the anode b.