By Kylene Arnold – Updated Mar 24, 2022
Normality expresses the number of equivalent hydrogen ions released by one liter of an acid in the presence of a base. For strong acids such as hydrochloric acid (HCl), this metric is preferable to molarity because it accounts for the single proton each molecule donates. A 0.5 N HCl solution therefore contains half an equivalent of hydrogen ions per liter, ensuring consistent reactivity across preparations.
Sum the atomic masses: hydrogen (1.007 g mol⁻¹) + chlorine (35.45 g mol⁻¹) = 36.457 g mol⁻¹.
Because each HCl molecule releases one H⁺, the equivalent mass equals the molar mass: 36.457 g eq⁻¹.
Use the formula: × (EqM × N × L). For 1 L of 0.5 N solution, 36.457 g eq⁻¹ × 0.5 N × 1 L = 18.2285 g of pure HCl.
Commercial HCl is typically 37 % w/w with a specific gravity of 1.19 g mL⁻¹. Calculate the volume of stock acid required: 18.2285 g ÷ (0.37 × 1.19) = 41.4 mL.
1. Fill a beaker with distilled water to approximately 500 mL (half the target volume). 2. Add the 41.4 mL of concentrated HCl slowly while stirring continuously to avoid localized overheating. 3. Once fully mixed, top off the solution with distilled water to reach exactly 1 L.
Follow all laboratory safety protocols when handling concentrated acids, and dispose of excess solution in accordance with local regulations.
