By Claire Gillespie | Updated March 24, 2022
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A saline solution is simply a mixture of sodium chloride (salt) and water. In a weight‑percent (w/v) solution, the salt is the solute and the water is the solvent. The calculation follows the formula:
w/v = (mass of solute ÷ volume of solution) × 100%
Because water’s density is 1 g/mL, 1 mL of water weighs 1 g, which simplifies the math.
Decide how much solution you require. For example, 200 mL of a 5 % saline solution.
Multiply the target volume by the desired percentage in decimal form: 200 mL × 0.05 = 10 g of salt.
Using the digital scale, measure 10 g of salt. Accuracy at this step is crucial for the final concentration.
Pour the measured salt into a graduated cylinder or volumetric flask that already contains roughly 180 mL of water. Gently swirl or stir until the salt has completely dissolved.
Top up with additional water until the total volume reads 200 mL. Adding the salt first and then filling to the mark ensures the correct concentration—adding 200 mL of water first would over‑dilute the solution.
Following these steps guarantees a precise 5 % saline solution, suitable for laboratory experiments, medical preparations, or other applications that require a consistent concentration.
