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How to Calculate Percent by Mass of a Solution?

Published in Solution Concentration 3 mins read

The percent by mass of a solution is calculated by dividing the mass of the solute by the total mass of the solution and then multiplying by 100.

Understanding Percent by Mass

Percent by mass is a way to express the concentration of a solution. It represents the mass of the solute as a percentage of the total mass of the solution. This is useful in chemistry for determining the composition of mixtures.

Formula for Percent by Mass

The formula to calculate percent by mass is:

Percent by Mass = (Mass of Solute / Mass of Solution) * 100

Where:

  • Mass of Solute is the mass of the substance being dissolved.
  • Mass of Solution is the total mass of the solution, which includes the mass of the solute and the mass of the solvent.

Steps to Calculate Percent by Mass

  1. Identify the Solute and Solvent: Determine which substance is the solute (the substance being dissolved) and which is the solvent (the substance doing the dissolving).
  2. Determine the Mass of the Solute: Find the mass of the solute, usually given in grams.
  3. Determine the Mass of the Solvent: Find the mass of the solvent, usually given in grams or milliliters (assuming density is known for volume conversions to mass).
  4. Calculate the Mass of the Solution: Add the mass of the solute and the mass of the solvent to get the total mass of the solution.
  5. Apply the Formula: Use the formula for percent by mass to calculate the percentage.

Example Calculation

According to the reference video, let's say you have 15 grams of NaCl (solute) and 100 grams of water (solvent).

  • Mass of Solute (NaCl): 15 grams
  • Mass of Solvent (Water): 100 grams
  • Mass of Solution: 15 grams + 100 grams = 115 grams
  • Percent by Mass: (15 grams / 115 grams) * 100 = 13.04% (approximately)

Therefore, the percent by mass of the NaCl solution is approximately 13.04%.

Key Considerations

  • Units: Ensure that the mass of the solute and the mass of the solution are in the same units (e.g., grams).
  • Solution Mass: Remember to include both the solute and solvent masses when calculating the total mass of the solution.

Practical Insights

  • Percent by mass is independent of temperature changes because the mass does not change with temperature.
  • It is commonly used in chemistry and other scientific fields when working with mixtures.
  • This calculation helps in determining the concentration of components in solutions and mixtures accurately.

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