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IGNOU BCHET-141 (January 2026 – December 2026) Assignment Questions
Part A
1 Give the details of the preservation techniques used for water samples.
2 A sample was analyzed for desired constituent having 3.67 g as the true value. The results of three measurements were 3.70 g, 3.74 g, and 3.77 g. Find the error of the mean (mean error), the percent relative error and the relative accuracy of the mean of the measurements.
3 Give the differences between t-test and F-test with the help of suitable examples.
4 With the help of suitable examples differentiate between the terms-distribution coefficient and distribution ratio.
5 Give the mechanism of extraction by solvation.
6 With the help of suitable equations explain the method solvent extraction with Diphenythiocarbazone.
7 Give the advantages of using continuous extraction?
8 With the help of a suitable diagram explain development of chromatogram along with the use of standard samples.
9 How does surface area of the stationary phase affect the separation in coloumn chromatography? What should be the sample to absorbent ratio so that clear separations are obtained?
10 What are the different types of ion exchangers? Give examples of a strong cation exchanger and a strong anion exchanger alongwith their specific functional groups.
Part B
11 A mixture of CaO and CaCO3 is analysed by TGA. The result indicates that mass of the sample decreases from 320.8 mg to 230.6 mg only between 650°C and 850°C. Calculate the percentage of calcium carbonate in the mixture.
12 Explain the method of pH metric titrations. Draw the different types of pH titration curves and show how equivalence points can be found from them
13 From the following data, calculate the molar conductivity of NaCl in aqueous
solution:
Conductivity of 4.0 × 10-4 mol dm-3 NaCl solution = 6.20 × 10-3 S m⁻¹
Conductivity of the water = 0.05 × 10-3 S m⁻¹.
14 With the help of suitable diagrams explain the typical conductometric titration curves for the following:
a) Strong acid with a strong base
b) Strong acid with a weak base
c) Precipitation titration
15 At 298 K, the limiting molar ionic conductivities of K⁺ and Cl⁻ ions are 73.5 and 76.3 S cm² mol⁻¹ respectively. Calculate:
(a) the transport number of K⁺ ions, and
(b) the transport number of Cl⁻ ions.
16 An infrared radiation has a frequency of 8 gigahertz.
(a) Calculate the energy of a photon corresponding to this radiation.
(b) Determine the wavelength of the radiation.
(Given h = 6.626 × 10 –34 J s and 1 gigahertz = 109 Hz)
17 With the help of a suitable diagram explain the absorption of radiation causing
(a) transitions in rotational energy levels
(b) transitions in vibrational energy levels of the molecule.
18 (a) What is the role of absorbing species in UV-VIS spectra? What are its different types?
(b) The molar absorptivity of a substance is 1.5 × 104cm‒1 mol‒1 dm3. Calculate the transmittance through a cuvette of path length 4.0 cm containing 3.0 × 10‒6 mol dm‒3 solution of the substance.
19 (a) What are the different types of IR spectrometers? Mention any one advantage of FT-IR spectrometer.
(b) What are the characteristic stretching frequencies for the following:
i) carboxylic acids ii) amides iii) nitroalkanes
20 Briefly compare the instrumentations for flame atomic absorption spectrophotometry and flame atomic emission spectrophotometry.
