A 45% (w/w) Potassium hydroxide can be purchased from several commercial suppliers. It is a clear colorless liquid and can be diluted to prepare solutions of known concentrations. Here we describe a procedure to prepare a 1 M Potassium hydroxide solution using commercially supplied 45% stock solution.
Reagents and solutions
45% (w/w) Potassium hydroxide solution
Equipment and disposables
Measuring cylinder/volumetric flask
Beaker (1 Liter)
Preparation of 1 Liter of 1M Potassium hydroxide using concentrated stock solution (45%, w/w)
Use personal protective equipment (lab coat, gloves, goggles etc) for your safety and follow the guidelines of your institute.
PART I: Calculate how much 45% (w/w) concentrated stock Solution is required to prepare 1 L of 1M Potassium hydroxide solution
Step 1: Calculate the molarity of 45% (w/w) concentrated Potassium hydroxide solution
The procedure to calculate molarity of 45% (w/w) concentrated Potassium hydroxide solution is described in detail in the post “Molarity of 45% (w/w) Potassium Hydroxide (KOH)”. From this post, you will know that the molarity of 45% (w/w) concentrated Potassium hydroxide solution is 11.677 M.
Step 2: Calculate how much concentrated stock solution is required to prepare 1L of 1M Potassium hydroxide solution using dilution method.
Dilution method is described in detail in the post “Preparing Working Solution from Stock Solution by Dilution”.
Use the following formula to calculate the volume of concentrated solution required for the preparation of 1 liter of 1M solution of hydrochloric acid solution
Formula: Cf x Vf = CS x VS
Cf (concentration of diluted (final) solution) = 1M
Vf (volume of diluted (final) solution) = 1 liter
CS (concentration of stock solution) = 11.677 M
VS (volume of stock solution) = ? (unknown)
Place all values in the formula:
1 x 1 = 11.677 x VS
VS = 1 x 1/ 11.677 = 0.0856 liter (85.6 ml)
So you need 0.0856 liter (85.6 ml) of 45% (w/w) concentrated Potassium hydroxide solution to prepare a 1 liter of 1M Potassium hydroxide solution.
Step 3: Calculate the volume of solvent to be taken.
Final volume of diluted solution = 1Liter
Volume of concentrated solution = 0.0856 liter
Volume of solvent (water) required = 1 – 0.0856 = 0.9144 Liter
So you need to mix 0.0856 liter (85.6 ml) of concentrated solution to 0.9144 liter (914.4 ml) water to prepare 1 liter of 1 M Potassium hydroxide solution.
PART II: Solution preparation
Step 4: Transfer 914.4 ml water in a beaker/volumetric flask/measuring cylinder. Add 85.6 ml of 45% Potassium hydroxide stock solution and mix it to prepare a homogeneous solution.
Note: In case you have not calculated the amount of water to be added, just take ≈ 500 ml water in a volumetric flask/measuring cylinder (capacity 1L) and add 85.6 ml of 45% Potassium hydroxide stock solution. Now adjust the final volume to 1 liter with water. Mix it.
Solution can be stored at room temperature.