Question

Calculate the pH of a solution in which one normal adult dose of aspirin (640 mg ) is dissolved in 10 ounces of water. Express your answer to one decimal place.

Answer 1

The pH of the solution in which one normal adult dose aspirin is dissolved is :  2.7

Given data :

mass of aspirin = 640 mg = 0.640 g

volume of water = 10 ounces = 0.295735 L

molar mass of aspirin = 180.16 g/mol

moles of aspirin = mass / molar mass = 0.00355 mol

Determine the pH of the solution

First step : calculate the concentration of aspirin

= moles of Aspirin / volume of water

= 0.00355 / 0.295735

= 0.012 M

Given that pKa of Aspirin = 3.5

pKa = -logKa

therefore ; Ka = $10^{-3.5}$ = $3.162 * 10^{-4}$

From the Ice table

$3.162 * 10^{-4}$ = $\frac{x + H^+}{[aspirin]}$  = $\frac{x^{2} }{0.012-x}$

given that the value of Ka is small we will ignore -x

x² = $3.162 * 10^{-4} * 0.012$

x = $1.948 * 10^{-3}$  

Therefore

[ H⁺ ] = $1.948 * 10^{-3}$

given that

pH = - Log [ H⁺ ]

     = - ( -3 + log 1.948 )

     = 2.71 ≈ 2.7

Hence we can conclude that The pH of the solution in which one normal adult dose aspirin is dissolved is :  2.7

Learn more about Aspirin : brainly.com/question/2070753