Overview
This lesson explains how to calculate weight/volume (w/v) concentrations, an essential skill for preparing pharmaceutical mixtures.
Weight/Volume Concentrations: Concepts
- Weight/volume (w/v) concentration describes grams of solute per 100 milliliters of total solution.
- Commonly involves a solid active ingredient dissolved in a liquid base (e.g., powder in syrup).
- Percent strength expresses the percentage of solute in the total mixture.
Calculating Weight/Volume Percent Strength
- The formula: (grams of solute ÷ milliliters of solution) × 100 = percent strength (% w/v).
- Step 1: Write the ratio of grams solute over total volume in milliliters.
- Step 2: Divide grams by milliliters to get a decimal.
- Step 3: Multiply the decimal by 100 to find the percentage.
Example Calculations
- Example 1: 25 g in 250 mL. Ratio: 25/250 = 0.1; 0.1 × 100 = 10%.
- Example 2: 10 g in 100 mL. Ratio: 10/100 = 0.1; 0.1 × 100 = 10%.
- Example 3: 5 g in 250 mL. Ratio: 5/250 = 0.02; 0.02 × 100 = 2%.
Key Terms & Definitions
- Weight/Volume (w/v) concentration — grams of solute per 100 milliliters of total solution.
- Percent strength — the percentage of active ingredient in the total mixture.
- Solute — the solid substance (active ingredient) being dissolved.
- Solution — the combination of solute and liquid base.
Action Items / Next Steps
- Practice calculating weight/volume concentrations using provided or new examples.
- Be prepared to test your understanding of these calculations.