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Other Units for Solution Concentrations

Other Concentration Units

While Molarity is the standard in chemistry labs, many medical applications use percentage-based units that are easier to calculate quickly at the bedside.

1. Mass Percentage (% w/w)

Defined as the mass of the solute divided by the total mass of the solution, multiplied by 100%.

✏️ Practice Problem: How many grams of NaOH are required to make 250 g of a 50% w/w solution?. Click for Solution

250 g solution * 0.50 (the decimal form of 50%) = 125 g of NaOH.

2. Volume Percentage (% v/v)

Used primarily for liquid-in-liquid solutions (like alcohol or throat sprays). It is the volume of solute per total volume of solution.

✏️ Practice Problem: How many mL of a 45% v/v glucose solution are needed to deliver 18 mL of pure glucose?. Click for Solution

18 mL glucose / 0.45 = 40 mL of solution.

3. Mass-Volume Percentage (% m/v)

This is the "gold standard" unit for clinical IV fluids. It represents the grams of solute per 100 mL of solution.


Vital Clinical Fact: Normal Saline is 0.90% w/v NaCl. This means there is exactly 0.90 g of NaCl in every 100 mL of saline.
✏️ Clinical Practice Problem: A patient receives 75 mL of 0.90% w/v saline per hour. How many grams of NaCl are delivered in 24 hours (1 day)?. Click for Solution
  1. Calculate total volume in 24 hours: 75 mL/hr * 24 hr = 1800 mL.
  2. Calculate grams of NaCl: 1800 mL * (0.90 g / 100 mL) = 16.2 g NaCl.

To master these concepts, try text problems: 69, 75, 77, and 79.