Question

Potassium hydroxide is very soluble in water, resulting in extremely basic solutions. A 121 g sample KOH is dissolved in water at 25 °C to make up 100.0 mL of solution. The molar mass of KOH is 56.11 3. What is the pH of the solution at 25.0°C? • Round the answer to two decimal places.

Answer 1

mass, m = 121 g

use:

number of mol,

n = mass/molar mass

=(1.21*10^2 g)/(56.11 g/mol)

= 2.156 mol

volume , V = 1*10^2 mL

= 0.1 L

use:

Molarity,

M = number of mol / volume in L

= 2.156/0.1

= 21.56 M

This is concentration of KOH

So,

[OH-] = 21.56 M

Given:

[OH-] = 21.56 M

use:

pOH = -log [OH-]

= -log (21.56)

= -1.3336

use:

PH = 14 - pOH

= 14 - -1.3336

= 15.3336

Answer: 15.33