Preparation of 1M Hydrofluoric Acid from Concentrated Stock Solution (48%, w/w)

OVERVIEW

A 48% (w/w) Hydrofluoric acid 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 Hydrofluoric acid solution using commercially supplied 48% stock solution. Remember that the molarity of Hydrofluoric acid is equal to the normality of the solution, which means 1M solution is also a 1N solution.

REQUIREMENTS

Reagents and solutions
48% (w/w) Hydrofluoric acid stock solution
Distilled water

Equipment and disposables
Measuring cylinder/volumetric flask
Beaker (1 Liter)
Magnetic stirrer

OBJECTIVE
Preparation of 1 Liter of 1M Hydrofluoric Acid using Concentrated Stock Solution (48%, w/w)

PROCEDURE

Use personal protective equipment (lab coat, gloves, goggles etc) for your safety and follow the guidelines of your institute.

PART I: Calculate how much 48% (w/w) concentrated Hydrofluoric acid stock solution is required to prepare 1 L of 1 M Hydrofluoric acid solution

Step 1: Calculate the molarity of 48% (w/w) concentrated Hydrofluoric acid solution
The procedure to calculate molarity of 48% (w/w) concentrated hydrofluoric acid solution is described in detail in the post “Molarity of 48% (w/w) Hydrofluoric Acid (HF)”. From this post, you will know that the molarity of 48% (w/w) concentrated hydrofluoric acid solution is 27.586M.

Step 2: Calculate how much stock solution is required to prepare 1L of 1M Hydrofluoric acid 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) = 27.586 M
VS (volume of stock solution) = ? (unknown)

Place all values in the formula:

1 x 1 = 27.586 x VS

VS = 1x 1/ 27.586 = 0.03625 liter (36.25 ml)

So you need 0.03625 liter (36.25 ml) of 48% (w/w) concentrated Hydrofluoric acid solution to prepare a 1 liter of 1M Hydrofluoric acid solution.

Step 3: Calculate the volume of solvent to be taken.

Final volume of diluted solution = 1Liter
Volume of concentrated solution = 0.03625 ml
Volume of solvent (water) required = 1 – 0.03625 = 0.96375 liter

So you need to mix 0.03625 liter (36.25 ml) of concentrated solution to 0.96375 liter (963.75 ml) water to prepare 1 liter of 1M Hydrofluoric acid solution.

PART II: Solution preparation

Step 4: Transfer 963.75 ml water in a beaker/volumetric flask/measuring cylinder. Add 36.25 ml of 48% concentrated Hydrofluoric acid 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 36.25 ml of  48% concentrated Hydrofluoric acid stock solution. Now adjust the final volume to 1 liter with water. Mix it.

STORAGE 
Solution can be stored at room temperature.

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