Question

Heroin (M_w = 369.42 g/mol) is weakly basic compound due to its tertiary amine group. The pK_a of its conjugate acid form is 7.95.

Six grams of a street drug containing heroin and calcium phosphate as the only components was shaken with 60 mL of chloroform. The chloroform was carefully decanted and evaporated to yield 738.84 mg of white solid, which was then dissolved in 300 mL of 6 mM HCl in water. This aqueous solution was divided into three equal aliquots. To the first aliquot, a full content of CO₂ soda charger was emptied but no precipitate formed. To the second aliquot, 1 mL of 1% bismuth nitrate was added but no precipitate formed. To the third aliquot, 2 mL of 5 M NaOH was added and a white precipitate formed. What was the pH of the third aliquot before the addition of 5 M NaOH?

Answer 1

Here, I express the pH of the solution. At fast I calculate PKb value of the weak base. When six grams of street drug shaken in 60 ml of chloroform then 738.84 mg heroin is precipitate. This heroin dissolved in 300 ml of 6mM HCl, and pH of the solution is 2.22, here heroin does not effect on pH because the concentration of H+ ion of HCl solution is much much higher than the heroin solution.