Question

Phenol (CH3OH), commonly called carbolic acid, is a weak organic acid. CH OH(aq) + H20(1) =CH20" (aq) + H30+ (aq) K. = 1.3 x 10-10 If you dissolve 0.715 g of the acid in enough water to make 767 mL of solution, what is the equilibrium hydronium ion concentration? (1,0+)-1 What is the pH of the solution? pH- Submit Answer Try Another Version 10 ltem attempts remaining

Answer 1

Molar mass of C6H5OH,

MM = 6*MM(C) + 6*MM(H) + 1*MM(O)

= 6*12.01 + 6*1.008 + 1*16.0

= 94.108 g/mol

mass(C6H5OH)= 0.715 g

use:

number of mol of C6H5OH,

n = mass of C6H5OH/molar mass of C6H5OH

=(0.715 g)/(94.11 g/mol)

= 7.598*10^-3 mol

volume , V = 7.67*10^2 mL

= 0.767 L

use:

Molarity,

M = number of mol / volume in L

= 7.598*10^-3/0.767

= 9.906*10^-3 M

C6H5OH dissociates as:

C6H5OH -----> H+ + C6H5O-

9.906*10^-3 0 0

9.906*10^-3-x x x

Ka = [H+][C6H5O-]/[C6H5OH]

Ka = x*x/(c-x)

Assuming x can be ignored as compared to c

So, above expression becomes

Ka = x*x/(c)

so, x = sqrt (Ka*c)

x = sqrt ((1.3*10^-10)*9.906*10^-3) = 1.135*10^-6

since c is much greater than x, our assumption is correct

so, x = 1.135*10^-6 M

So, [H+] = x = 1.135*10^-6 M

use:

pH = -log [H+]

= -log (1.135*10^-6)

= 5.9451

Answer:

[H3O+] = 1.13*10^-6 M

pH = 5.945