JNTU B.Pharmacy I Year PHARMACEUTICAL ANALYSIS-I Previous Question Paper (September/October- 2021 - R17)

Preparation of 0.1 M Ceric Ammonium Sulphate: Dissolve 63.26 g of ceric ammonium sulphate in 500 mL of distilled water containing 30 mL of concentrated sulfuric acid. Stir until dissolved, cool, and dilute to 1000 mL with distilled water. Standardization: Weigh accurately about 0.2 g of primary standard arsenic trioxide (dried at 105°C) into a flask. Dissolve in 20 mL of 1 M sodium hydroxide, then add 100 mL of water and 25 mL of 2 M sulfuric acid. Add 0.15 mL of osmic acid solution and 0.1 mL of ferroin indicator. Titrate with the ceric ammonium sulphate solution until the color changes from reddish-orange to pale blue. Calculate the molarity using the stoichiometry where 1 mole of arsenic trioxide reacts with 4 moles of ceric ammonium sulphate.

Preparation of 0.5 M Sulfuric Acid: Calculate the volume required using the density and percentage purity of concentrated sulfuric acid (approximately 27.7 mL of concentrated H2SO4 is required for 1000 mL). Add the calculated volume slowly to about 500 mL of distilled water with constant stirring, cool, and dilute to 1000 mL. Standardization: Weigh accurately about 1.5 g of anhydrous sodium carbonate (previously dried at 270°C). Dissolve in 50 mL of water and titrate with the sulfuric acid solution using methyl orange as an indicator until the color changes from yellow to orange-red. Calculate molarity based on the reaction: Na2CO3 + H2SO4 -> Na2SO4 + H2O + CO2.

Rounding off is essential to maintain the precision of analytical data. The rules are as follows:

• If the digit to be dropped is less than 5, the preceding digit remains unchanged.
• If the digit to be dropped is greater than 5, the preceding digit is increased by 1.
• If the digit to be dropped is exactly 5, the preceding digit is rounded to the nearest even number (e.g., 2.45 becomes 2.4, and 2.55 becomes 2.6).
• When multiple operations are performed, retain extra digits during intermediate calculations and round only the final result to the appropriate number of significant figures.