Normal Saline (0.9% NaCl): Chemistry, Concentration, and Clinical Use

Normal Saline

Normal saline (NS) = 0.9% w/v sodium chloride (NaCl) in water. Also called physiological saline or isotonic saline.

Chemical Basis

• NaCl molecular weight: 58.44 g/mol
• Valence (n-factor): 1
• Equivalent weight = 58.44 g/equiv
• 1 Normal (1 N) solution = 1 equivalent per liter = 58.44 g/L NaCl.
• 0.9% w/v = 9 g/L = 0.154 mol/L ≈ 0.154 N (since n=1).

Historically, "normal" referred to a 1 N solution, but 0.9% NaCl became the clinical standard because its osmolarity (~308 mOsm/L) approximates human plasma (~285–295 mOsm/L), making it isotonic.

Clinical Applications

• IV fluid resuscitation, maintenance, dilution vehicle
• Wound irrigation, catheter flush
• Nebulization vehicle
• Not for large-volume replacement in hyponatremia (use hypertonic) or hypernatremia (use hypotonic).

Key Point

Despite the name, 0.9% NaCl is not 1 N; it is ~0.154 N. The term "normal saline" is a clinical convention, not a chemical normality designation.