CH 3805 – ANALYTICAL CHEMISTRY – III

Date & Time : 26/06/2006/9.00 – 12.00 Dept. No. Max. : 100 Marks

PART – A

Answer ALL the questions. 10 x 2 = 20 marks

Mention the characteristics of a good set of Measurements.
A chloride sample containing bromide as contaminant is estimated by argentometric titration. What is the error associated with the result?
Calculate the pH of the mixture containing 20.00mL of 0.0250M CH₃COOH and 40.00mL of 0.0125M OH^–. K_a for CH₃COOH is 10^–5.
A little of Mg EDTA complex is added in the estimation of Ca⁺² using EDTA. Why?
What is the gravimetric factor for Fe⁺³, when it is precipitated as ferric hydroxide and weighed as ferric oxide?
Calculate the current required to deposit all the metal ions in 100 ml of 0.01M Cu₂Cl₂ in 30 minutes.
What is the difference between potentiometry and voltametry?
Explain why electroylysis of aqueous 1 M NaCl results in the liberation of hydrogen and not Na?
Explain the principle of AAS method of estimation of metal ions.
Mention any two applications of TGA.

PART – B

Answer any EIGHT questions. 8 x 5 = 40 marks

Compare the solubility of Mg(OH)₂ (Ksp Mg(OH)₂ = 10^–12 mol³dm^–9) in
i) 10^–2M La₂(SO₄)₃ ii) 10^–2M AlCl₃.
Analysis of Vitamin C content of a citrus fruit drink gave the following results. 0.218, 0.219, 0.215, 0.230 and 0.220 mg/mL. Calculate the 99% confidence interval if t_99% is 4.60.
Write a note on the acid base titration in non-aqueous solvent.
Discuss the factors which affect ate the equivalence point.
Compare the initial equivalence point pH for the following.
i) 20.00mL of 10^–2M, CH₃COOH Vs 10^–2M OH^–
ii) 20.00 mL of 10^–2 CHCl₂COOH Vs 10^–2M OH^–‑.
K_a for CH₃COOH is 10^–5 and K_a for CHCl₂ COOH is 10^–2.
Show that the equivalence point potential for Fe⁺² Vs MnO₄^–‑/H⁺ depends on pH.
Define half wave potential. How does it differ from standard reduction potential?
An aqueous solution of CdSO₄was analysed at its half-wave potential with a current of 0.6 A. Calculate the time required to lower the concentration of 10ml of Cd²⁺ solution from 2 x 10^–4 M to 1.9 x 10^–4M. What conclusion you can draw from the result?
Explain a coulometric method of estimation thiosulphate using iodide.
How will you estimate bromide by ampereometric titration?
Explain, with suitable diagrams, the difference between TGA and DTA.
Explain, with an example, the principle of i) steam distillation and ii) solvent extraction.

PART – C

Answer ALL the questions. 10 x 2 = 20 marks

The following data were obtained in calibrating a calcium ion electrode for the determination of pCa. A linear relationship between the potential E and pCa is known to exist.

pCa E mv

5.00 –53.8

4.00 –27.7

3.00 +2.7

2.00 +31.9

1.00 +65.1

i) Calculate the equation for the best straight line through these points.
ii) Obtain the pCa of a serum solution in which the electrode potential is 20.3mV, which is the mean of four measurements.

iii) Also calculate the standard deviation of the slope and the result.

Draw the titration curve for the titration of 20.00mL of 0.0250M Ni⁺² vs 0.01250M EDTA at pH 8 by finding out the p^Ni at the following stages: i) initial ii) pre-equivalence point iii) just before equivalence point iv) the equivalence point v) post equivalence point.
Keff for [Ni EDTA]^–2 is 10¹⁶ at pH 8.
i) Determine the concentration of all the species in the mixture containing 50 mL of 0.0500M Fe⁺² and 25mL of 0.1000M Ce⁺⁴ in 1.000M H₂SO₄. E⁰Ce⁺⁴/Ce⁺³ = 1.5V; E⁰Fe⁺³ /Fe⁺² = 0.70V
ii) A 0.6200g sample containing NaCl and NaBr gives 0.5120g precipitate of silver halide. Another 0.6200g sample containing NaCl and NaBr gives 0.5120g precipitate of silver halide. Another 0.6200g sample is titrated with 0.1070M AgNO₃ requiring 28.10mL. Calculate the percentages of NaCl and NaBr in the sample.