askvity

How to Calculate the Concentration of a Mixed Solution?

Published in Solution Concentration 3 mins read

To calculate the concentration of a mixed solution, especially when combining solutions of the same solute, you need to determine the total moles of solute and the total volume of the solution. Here’s a breakdown of the process:

Steps to Calculate the Concentration of a Mixed Solution

  1. Calculate Moles in Each Solution: First, determine the number of moles of solute in each individual solution before mixing. This is typically done using the formula:

    Moles = Concentration × Volume

    Where:

    • Concentration is typically in molarity (M), which is moles per liter (mol/L).
    • Volume is in liters (L). If the volume is given in milliliters (mL), convert it to liters by dividing by 1000.

  2. Add Up the Moles: Once you've calculated the moles of solute in each solution, add them together to find the total number of moles of solute in the mixed solution.

    Total Moles = Moles₁ + Moles₂ + Moles₃ + ...

  3. Determine the Total Volume: Calculate the total volume of the mixed solution by adding the volumes of all the individual solutions together. Make sure all volumes are in the same unit (preferably liters).

    Total Volume = Volume₁ + Volume₂ + Volume₃ + ...

  4. Calculate the Final Concentration: Finally, calculate the concentration of the mixed solution by dividing the total moles of solute by the total volume of the solution.

    Final Concentration = Total Moles / Total Volume

    The result will be the concentration of the mixed solution, usually expressed in molarity (M).

Example Calculation

Let's say you have two solutions of NaCl (sodium chloride):

  • Solution 1: 2.0 L of 0.5 M NaCl
  • Solution 2: 3.0 L of 1.0 M NaCl

Here's how to calculate the concentration of the mixed solution:

  1. Calculate moles in Solution 1:

    Moles₁ = 0.5 M × 2.0 L = 1.0 mol

  2. Calculate moles in Solution 2:

    Moles₂ = 1.0 M × 3.0 L = 3.0 mol

  3. Calculate total moles:

    Total Moles = 1.0 mol + 3.0 mol = 4.0 mol

  4. Calculate total volume:

    Total Volume = 2.0 L + 3.0 L = 5.0 L

  5. Calculate the final concentration:

    Final Concentration = 4.0 mol / 5.0 L = 0.8 M

Therefore, the concentration of the mixed NaCl solution is 0.8 M.

Key Considerations

  • Units: Always ensure that the units are consistent throughout the calculation. Convert all volumes to liters and use molarity (mol/L) for concentration.
  • Additive Volumes: Assume volumes are additive unless otherwise stated. In some cases, mixing solutions can result in a slight volume change, but this is often negligible.
  • Same Solute: This method applies when mixing solutions containing the same solute. If different solutes are mixed and react, the calculation becomes more complex and requires stoichiometry.

By following these steps, you can accurately calculate the concentration of a mixed solution, ensuring correct results in your chemical calculations and experiments.

Related Articles