Mixed percentage units, derived from the mass of solute and the volume of solution, are popular for certain biochemical and medical applications. Mass-volume percent is usually abbreviated as **%m/v** or **%w/v** when used. A mass-volume percent is a ratio of a solute’s mass to the solution’s volume expressed as a percentage. The specific units used for solute mass and solution volume may vary, depending on the solution, but are usually assumed to be **grams of solvent and mL of solution** if not specified:

$$\%\;m/v = \frac{g\;\text{solute}}{mL\;\text{solution}}\times 100\%$$

#### Calculating with % m/v

Physiological saline solution, seen above, is generally a 0.9 % m/v solution of sodium chloride (NaCl) in water. What mass of sodium chloride would be needed to make a 250 mL intravenous bag of saline solution?

#### Solution

We can solve this problem using the unit analysis method: $$0.9\:\%m/v\;\text{NaCl} = \frac{x\; \text{g NaCl}}{250\;\text{mL saline}} \times 100\% \\ \left(\frac{0.9\times 250}{100} \right) = x\; \text{g NaCl} \\ =0.225 \; \text{g NaCl} \\ =0.2\; \text{g NaCl} $$