Question

Propofol (178.23g/mol) is an anesthetic widely used in surgery and involved in the death of Michael Jackson. It is a weaking acidic drug that is soluble in water and has a pKa of 11.1. If 1,131.8mg of propofol was dissolved in a 1.00L IV bag (aqueous solution), what would be the pH of this solution? Report to 2 decimal places

Answer 1

Mass of Propofol = 1131.8 mg = 1.318 g

Molar mass of Propofol = 178.23 g/mol

Moles of Propofol = 1.318 / 178.23

= 0.0074

Volume of solution = 1.0 L

Molarity of Propofol solution = 0.0074 / 1.0

= 0.0074

pKa of Propofol = 11.1

Ka = 10^-pKa

= 10^-11.1

= 7.94*10^-12  

Let us denote the Propofol by HA (weak acid).

HA    H⁺   + A^-  
Initial 0.0074 0 0
Change -x +x +x
Final 0.0074 - x x x

Ka = [H⁺][A^-] / [HA]

7.94*10^-12 = x*x / (0.0074 - x)

x = 2.42*10^-7

So, [H⁺] = 2.42*10^-7 M

pH = - log [H⁺]

= - log (2.42*10^-7)

pH = 6.61