The phrase "10% glucose solution" can lead to confusion if the unit of measurement is not specified. In scientific and medical fields, precision is paramount, and understanding the difference between weight/volume (w/v) and weight/weight (w/w) concentrations is crucial for accurate calculations and solution preparation.
Understanding Percentage Concentration
What is Weight/Volume (w/v) Percentage?
In a weight/volume percentage concentration, the amount of solute is expressed in grams, and the volume of the final solution is expressed in milliliters. A 10% (w/v) solution means that for every 100 mL of the final solution, there are 10 grams of solute dissolved within it. For example, to make 100 mL of a 10% (w/v) glucose solution, you would dissolve 10 grams of glucose in a smaller volume of water and then add enough water to bring the total volume up to 100 mL.
What is Weight/Weight (w/w) Percentage?
A weight/weight percentage concentration describes the mass of the solute in grams relative to the total mass of the solution in grams. A 10% (w/w) solution contains 10 grams of solute for every 100 grams of the final solution. To prepare a 10% (w/w) glucose solution, you would dissolve 10 grams of glucose in 90 grams of water, resulting in a total solution mass of 100 grams. This concentration type is independent of temperature, unlike w/v, which is affected by volume changes due to temperature fluctuations.
Why the Difference Matters
Failing to distinguish between these two methods can lead to significant errors in applications ranging from laboratory experiments to intravenous fluid administration. The difference can be substantial, especially when dealing with large volumes. A 10% w/v solution and a 10% w/w solution have different densities and therefore contain different masses of solute per unit volume.
Calculating Grams of Glucose
Calculation for a 10% (w/v) Solution
Calculating the mass of glucose for a given volume of a 10% (w/v) solution is straightforward. The formula is:
$Mass of Glucose (g) = (Volume of Solution (mL) / 100) × 10$
Example Calculations:
- For 100 mL: $(100/100) × 10 = 10$ grams of glucose.
- For 500 mL: $(500/100) × 10 = 50$ grams of glucose.
- For 1 Liter (1000 mL): $(1000/100) × 10 = 100$ grams of glucose.
Calculation for a 10% (w/w) Solution
To calculate the mass of glucose in a 10% (w/w) solution for a specific total solution mass, the formula is:
$Mass of Glucose (g) = (Total Mass of Solution (g) / 100) × 10$
Example Calculations:
- For 100 grams of solution: $(100/100) × 10 = 10$ grams of glucose.
- For 50 grams of solution: $(50/100) × 10 = 5$ grams of glucose.
Comparison of W/V and W/W Percentage
| Feature | Weight/Volume (w/v) | Weight/Weight (w/w) |
|---|---|---|
| Definition | Grams of solute per 100 mL of solution | Grams of solute per 100 grams of solution |
| Preparation Method | Dissolve solute and bring total volume to 100 mL | Dissolve solute in solvent to achieve total mass of 100 g |
| Common Use | Clinical settings, lab work with liquids | Industrial processes, solid-in-liquid mixtures |
| Affected by Temperature? | Yes, volume changes with temperature | No, mass is unaffected by temperature |
| Need for Density | Not required for basic calculations | Needed to convert to w/v or molarity |
Conclusion
In summary, the number of grams of glucose in a 10% solution is entirely dependent on the method of concentration measurement. A 10% weight/volume (w/v) solution contains 10 grams of glucose per 100 mL of solution, a common standard in many applications. A 10% weight/weight (w/w) solution contains 10 grams of glucose for every 100 grams of total solution mass. Always confirm the concentration type when preparing or working with solutions to ensure accuracy and prevent potential errors. For more detailed information on solution concentrations, refer to a reliable chemistry resource such as the Chemistry LibreTexts page on solution concentrations.
Preparing a 10% (w/v) Glucose Solution (Step-by-Step)
- Measure: Accurately measure 10 grams of glucose using an electronic balance.
- Combine: Add the measured glucose to a volumetric flask or beaker.
- Dissolve: Add a smaller amount of distilled water to the flask and stir or swirl until the glucose is completely dissolved.
- Fill to Volume: Carefully add more distilled water until the total volume of the solution reaches the 100 mL mark on the flask.
- Mix: Mix the solution thoroughly to ensure homogeneity.
- Label: Label the container with the concentration (10% w/v), name (glucose), and date.
