Analytical Methods in Chemistry — DU B.Sc (hons) Chemistry Previous Year Question Papers

-- The question paper 'consists of 8 questions in all. (b) In a dataset of five measurements: 12.4, 12.6, 12.5, 12.7, 12.3, compute the mean, standard deviation and relative standard deviation. Give an outline of the general steps involved in an analytical procedure. Briefly describe each step. 5,5,5 (a) Compare the operations of a single beam and a double beam spectrophotometer. (b) What are the drawbacks of the Beer Lambert's law. A 20 ppm solution of a DNA molecule (unknown molecular weight) isolated from Escherichia coli was found to give an absorbance of 0.80 in a 2 cm cell. Calculate the absorptivity of the molecule.. 3.: (a) What is Thermogravimetry.? What are the various components of a thermobalance ? Explain working of a thermobalance giving a schematic diagram. (b) Enumerate the principle of TGA and write down any four applications of TGA. (c) A mixture, of CaO and CaCOz, is analyzed using TGA technique. The TG curve of the sample shows a change of mass from 150 mg to 110 mg between 650°C and 920°C. Calculate the percentage of calcium carbonate in the mixture. 5,5,5 (a) Explain the method of solvent extraction using continuous process when the organic phase (extractant) is heavier than water with the help of a diagram. - (b) 5g of compound A is dissolved in. in. ml of water. -The partition coefficient for compound A between hexane and' water is 5. (i) How much of compound A will be extracted in hexane if it is extracted from aqueous solution with 90 mL of hexane ? (it) How much of compound A will be extracted in hexane if three consecutive extractions are performed using 30 ml of hexane each time and then combine the hexane extracts ? (e) Describe two principal solvent extraction systems for metal ions. Give examples of each. Ninety-six percent of a solute is removed from 100 ml of an aqueous solution by extraction with two 50 ml. portions of an organic solvent. What is the distribution ratio of the Explain the process of sample delivery in flame spectroscopy and describe how atomization of the sample is achieved during the analysis. (b) Discuss the importance of obtaining good resolution in chromatography. Describe other factors influencing the separation of == components in chromatography. (e) Classify different, chromatographic techniques and their underlying principles. Discuss various applications of chromatography. 5,5,5 6. (a) Discuss various equilibrium processes involved. the solvent extraction of metal ion from an aqueous solution using a chelating agent. Write an expression the distribution ratio (D) of the chosen system. Mention the condition for better extraction of metal chelates (b) What is a Q-test in analytical chemistry? Discuss how is it useful in rejecting or retaining of data obtained for an experiment. (c) Compare flame emission spectrometry and flame, atomic absorption spectrometry with respect to applicability of instrumentation, sensitivity and interferences. 5,5,5