OVERVIEW

•  A 37% (w/w) Hydrochloric Acid is a clear colorless aqueous solution of Hydrogen chloride (HCl) gas. It can be purchased from several commercial suppliers.
• The “%” refers to solution concentration in percent and “(w/w)” refers to solute and solution amount given in grams (i.e., percentage by weight). This means a 37% (w/w) Hydrochloric acid contains 37 g of HCl per 100 g of solution.
  
• The density of 37% (w/w) Hydrochloric acid solution is 1.2 g/ml at 25° C. This means the weight of the 1 ml of the hydrochloric acid solution is 1.2 g at 25°C.
• Molarity refers to the number of moles of the solute present in 1 liter of solution. To calculate the Molarity of 37% (w/w) Hydrochloric Acid (HCl), you need to know how many moles of HCl 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 chloride is equal to 36.46 g of hydrogen chloride (Molecular Weight: 36.46).
• To calculate the molarity, one must first calculate how much Hydrogen chloride is present in 1 L of 37% Hydrochloric acid. Once we know the amount of HCl present in 1 L solution, we can calculate the molarity of the solution by dividing the HCl amount by the molecular weight.
  

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• Molarity of 37% (w/w) Hydrochloric Acid (HCl)
• How to Calculate Molarity of 37% (w/w) Hydrochloric acid (HCl), Alternative Method

Calculation procedure

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

Density = $\frac{Weight}{Volume}$ 

OR

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

The volume of 100 g of Hydrochloric acid : $\frac{100}{1.2}$  = 83.33 ml

Note: 37% (w/w) Hydrochloric acid means that 100 g of Hydrochloric acid contains 37 g of HCl.

The volume of 100 g of Hydrochloric acid is 83.33 ml which means 37 g of HCl is present in 83.33 ml of Hydrochloric acid.

Step 2: Calculate how many grams of HCl is present in 1000 ml of Hydrochloric acid.

83.33 ml of Hydrochloric acid contains   = 37 grams of HCl
1 ml of Hydrochloric acid will contain      =   $\frac{37}{83.33}$  grams of HCl

1000 ml of Hydrochloric acid will contain =   $\frac{\mathrm{37\; x\; 1000}}{83.33}$  grams of HCl  = 444.01776 grams of HCl

1000 ml of Hydrochloric acid will contain 444.01776 grams of HCl.

Step 3: Calculate the number of moles of HCl in 444.01776 grams of HCl.

36.46 g of HCl is equal to 1 mole.

1 g of HCl will be equal to $\frac{1}{36.46}$  moles.

444.01776 grams of Hydrogen chloride will be equal to = $\frac{444.01776 \mathrm{x} 1}{36.46}$ $\frac{444.01776 \mathrm{x} 1}{36.46}$ = 12.178 moles

Therefore, we can say that 1 liter of Hydrochloric acid contains 12.178 moles of HCl or in other words molarity of 37% (w/w) Hydrochloric acid is equal to 12.178 M.