Question

TIME ALLOWED IHOUR 1. A total of twenty (20) tablets (suspected to contain cocaine was previously dried over silica gel) were crushed by an analytical Pharmaceutical Chemist working with a Drug Law Enforcement Agency. The total weight of the powder obtained was 9.3g. A specified amount of the powder, 0.2g was dissolved in a mixture of 40mL glacial acetic acid and 10mL mercuric acetate. Two drops of quinaldine red was added and the solution was titrated with 6.25mL of 0.IN perchloric acid (correction factor 0.1115). A blank determination was found to consume 0.25mL (ImL of Perchloric Acid 0.021124g, Each tablet of cocaine contains API 365mg, M.Wt 339.8g) In one sentence, describe the role of correction factor in this analysis What is the exact volume of the acid used during the analysis? Using appropriate equations, briefly explain why the Chemist dried the suspected powder over silica gel. (3marks) d. List 2 indicators that are colorless in acidic medium. Draw the titration curve of a Strong Acid Strong Base. Briefly explain why it is neutral at equivalence point. (3 marks) Calculate the percentage content of cocaine in the suspected powder a. (Imark) (Imark) b. c. (2marks c. (10marks)

Answer 1

Part a.

The role of the correction factor is to minimize errors.

Part b.

The exact volume of the acid (perchloric acid) used = 6.25 - (6.25 * 0.1115) = 5.55 mL

Part c.

Silica can absorb the cocaine (if present) in the suspected powder because both silica (SiO₂) and cocaine (C₁₇H₂₁NO₄) are polar, as a result, they interact with each other.

Part d.

(i) Phenolphthalein

(ii) Thymolphthalein

(iii) 2,4-Dinitrophenol

(iv) p-Nitrophenol

The above indicators are colorless in acidic medium.