Understanding Mass Percentage: The Basics
Mass percentage, often denoted as %m/m or %w/w, is a fundamental way to express the concentration of a solution. It is defined as the mass of the solute divided by the total mass of the solution, multiplied by 100. The total mass of a solution is the sum of the mass of the solute and the mass of the solvent. For a "10% glucose in water by mass" solution, this means a clear quantitative ratio of the components.
The Calculation Explained
A 10% glucose in water by mass solution contains 10 grams of glucose for every 100 grams of the final solution. The remaining 90 grams in 100 grams of solution is water. The composition of a 100 g solution is:
- Mass of solute (glucose) = 10 g
- Mass of solution = 100 g
- Mass of solvent (water) = Mass of solution - Mass of solute = 100 g - 10 g = 90 g
This mass-based measurement is valuable because it is temperature-independent, unlike volume-based units such as molarity. This makes mass percentage reliable for industrial processes where temperatures may vary.
How to Prepare a 10% Glucose Solution by Mass
Preparing a 10% glucose solution by mass requires careful measurement. To create a 100 g solution:
- Gather Materials: You will need a weighing scale, a container, solid glucose, and distilled water.
- Weigh the Glucose: Measure 10 g of glucose accurately into the container.
- Add the Water: Add exactly 90 g of distilled water to the glucose.
- Mix Thoroughly: Stir until the glucose is fully dissolved. This results in a 10% glucose solution by mass.
- Scaling: The 1:9 ratio of glucose to water by mass in the solution can be scaled. For example, a 200 g solution would use 20 g of glucose and 180 g of water.
Comparison of Concentration Units
Different concentration units are used in chemistry. Here's a comparison of mass percentage with molarity and mass/volume percentage:
| Feature | Mass Percentage (% m/m) | Molarity (M) | Mass/Volume Percentage (% m/v) |
|---|---|---|---|
| Definition | Mass of solute per 100g of solution | Moles of solute per liter of solution | Mass of solute per 100ml of solution |
| Temperature Dependence | Temperature-independent | Temperature-dependent due to volume changes | Temperature-dependent due to volume changes |
| Unit of Measurement | % m/m or %w/w | mol/L | % m/v |
| Common Applications | Industrial chemistry, food production, intravenous fluids | Laboratory reagents, stoichiometry calculations | Medical labs, pharmaceutical preparations |
Applications and Relevance
Defining concentration by mass percentage is crucial in various fields. In medicine, specific mass percentage concentrations are used for intravenous (IV) fluids like 10% dextrose to provide calories and fluid. The food and beverage industry uses mass percentages to ensure product consistency and sweetness. The temperature independence of mass percentage makes it a reliable tool for quality control in manufacturing. Understanding a 10% glucose in water by mass solution is a foundational concept in quantitative chemistry, ensuring clarity and consistent results.
Common Misconceptions to Avoid
Avoid confusing the mass of the solvent with the total mass of the solution. A 10% mass/mass solution is 10g of glucose in a total of 100g of solution, not 10g of glucose in 100g of water. Mass percentage and molarity are not interchangeable as molarity is temperature-sensitive. Always use consistent mass units for calculations.
Conclusion
In conclusion, a "10% glucose in water by mass" solution means that 10% of the total mass of the solution is glucose, and the remaining 90% is water. This temperature-independent unit is a reliable standard in science, medicine, and industry, allowing for accurate calculation and preparation of solutions for various applications. Its clarity makes mass percentage a cornerstone of quantitative chemistry. For further reading on solution concentrations, see LibreTexts Chemistry.
