Understanding Concentration
* Concentration: A measure of how much solute (the substance being dissolved) is present in a given amount of solvent (the substance doing the dissolving). Common units include:
* Molarity (M): Moles of solute per liter of solution.
* Percent Concentration (%): Grams of solute per 100 grams or milliliters of solution.
* Parts per million (ppm): Milligrams of solute per liter of solution.
Dilution: Making a Solution Less Concentrated
Dilution is the process of adding more solvent to a solution to decrease its concentration. Here's the key formula:
* M₁V₁ = M₂V₂
Where:
* M₁: Initial concentration (molarity) of the concentrated solution.
* V₁: Volume of the concentrated solution you'll use.
* M₂: Desired final concentration (molarity) of the diluted solution.
* V₂: Final volume of the diluted solution.
Steps for Dilution
1. Determine the desired final concentration (M₂) and final volume (V₂) of the diluted solution.
2. Calculate the volume (V₁) of the concentrated solution needed using the formula M₁V₁ = M₂V₂. Solve for V₁: V₁ = (M₂V₂) / M₁
3. Measure out the calculated volume (V₁) of the concentrated solution.
4. Add enough solvent (typically water) to reach the desired final volume (V₂).
Example
Let's say you have a 2 M solution of sodium chloride (NaCl) and want to make 500 mL of a 0.5 M NaCl solution:
* M₁ = 2 M (concentration of the stock solution)
* V₁ = ? (volume of the stock solution we need to use)
* M₂ = 0.5 M (desired concentration of the diluted solution)
* V₂ = 500 mL (desired final volume of the diluted solution)
Using the formula: V₁ = (M₂V₂) / M₁ = (0.5 M * 500 mL) / 2 M = 125 mL
1. Measure out 125 mL of the 2 M NaCl solution.
2. Add enough water to make the total volume 500 mL.
Important Notes:
* Always add the concentrated solution to the solvent, not the other way around. This helps ensure proper mixing and prevents potential hazards.
* Use appropriate glassware for accurate volume measurements.
* For solutions with specific safety precautions, follow the instructions carefully.
Making a Solution from a Different Concentration Unit
If you are starting with a concentration unit other than molarity, you'll need to convert it to molarity first. Here's a general approach:
1. Convert the concentration to molarity (M). This may involve using the molecular weight of the solute and appropriate conversion factors.
2. Follow the dilution steps above using the calculated molarity.
Let me know if you'd like more specific examples or have any other questions!
