OVERVIEW

• A 48% (w/w) Hydrofluoric acid (HF) is a clear colorless aqueous solution of Hydrogen fluoride (HF) gas. It can be purchased from many commercial suppliers.
• % refers to solution concentration in percentage and “(w/w)” refers to solute and solution amount given in grams (i.e., percentage by weight). This means a 48% (w/w) Hydrofluoric acid contains 48 g of Hydrogen fluoride (HF) per 100 g of solution.
  
• The density of 48% hydrofluoric acid is 1.15 g/ml at 25° C. This means the weight of the 1 ml of hydrofluoric acid is 1.15 g at 25°C.
• Molarity refers to the number of moles of the solute per litre of solution. To calculate the Molarity of 48% (w/w) Hydrofluoric Acid, you need to know how many moles of HF are present in 1 liter of solution.
  
• In simple words, 1 mole is equal to the molecular weight of the substance. For example, 1 mole of Hydrogen fluoride is equal to 20.01 g of Hydrogen fluoride (Molecular Weight: 20.01).
• To calculate the molarity, one must first calculate how much Hydrogen fluoride is present in 1 L of 48% Hydrofluoric acid. Once we know the amount of HF present in 1 L solution, we can calculate the molarity of the solution by dividing the HF amount by the molecular weight.
• Calculator: Converting Percentage by Mass to Molarity

Calculation procedure

Step 1: Calculate the volume of 100 grams of Hydrofluoric acid.
Formula:

Density = $\frac{Weight}{Volume}$

OR

Volume = $\frac{\mathrm{Weight}}{\mathrm{Density}}$

The volume of 100 g of Hydrofluoric acid : $\frac{100}{1.15}$ = 86.9565 ml

Note: 48% (w/w) Hydrofluoric acid means that 100 g of Hydrofluoric acid contains 48 g of HF.

The volume of 100 g of Hydrofluoric acid is 86.9565 ml which means 48 g of HF is present in 86.9565 ml of Hydrofluoric acid.

Step 2: Calculate how many grams of HF is present in 1000 ml of Hydrofluoric acid.

86.9565 ml of Hydrofluoric acid contains   = 48 grams of HF
1 ml of Hydrofluoric acid will contain      =   $\frac{48}{86.9565}$ grams of HF

1000 ml of Hydrofluoric acid will contain = $\frac{1000 x 48}{86.9565}$  = 552 grams of HF

1000 ml of Hydrofluoric acid will contain 552 grams of HF.

Step 3: Calculate the number of moles of HF in 552 grams of HF.

20.01 g of HF is equal to 1 mole.

1 g of HF will be equal to $\frac{1}{20.01}$ moles.

552 grams of Hydrogen fluoride will be equal to = $\frac{552 \mathrm{x} 1}{20.01}$ = 27.46 moles

Therefore, we can say that 1 liter of Hydrofluoric acid contains 27.46 moles of HF or in other words molarity of 48% (w/w) Hydrofluoric acid is equal to 27.46 M.