How to Dilute a 1000 ppm Stock Solution to 0.01 M in a 50 mL Flask

When working in a laboratory, precise calculations are essential for diluting stock solutions to the desired concentration. This article provides a step-by-step guide on how to dilute a 1000 ppm stock solution to a 0.01 M concentration in a 50 mL flask, based on the molar mass of the solute.

Understanding the Terms: Molarity and ppm

Molarity (M) is defined as the number of moles of solute per liter of solution, commonly used in laboratory settings for expressing solution concentration. Parts per million (ppm) is another way to express concentration, specifically used when dealing with very dilute solutions. It is defined as the mass of solute in milligrams (mg) per liter (L) of solution.

Step-by-Step Guide to Dilution

To dilute a 1000 ppm stock solution to a 0.01 M (molar) concentration in a 50 mL flask, you need the molecular weight (molar mass) of the solute to perform the necessary calculations. The process involves several key steps:

Step 1: Identify the Solute’s Molar Mass

The first step is to determine the molar mass (MW) of the solute. This value is crucial in converting between molarity and ppm. The molar mass is the mass of one mole of a substance and is typically found in the periodic table or provided in the solution’s specifications.

Step 2: Convert ppm to Molarity

The conversion from ppm to molarity (M) is given by the formula:

Molarity (M) (ppm / MW) x 10-3

For instance, if the solute is sodium chloride (NaCl), which has a molar mass of 58.5 g/mol, the calculation would be:

0.0171 M (1000 ppm / 58.5 g/mol) x 10-3

This shows that the stock solution, at 1000 ppm, is equivalent to 0.0171 M.

Step 3: Calculate the Required Volume of Stock Solution

To achieve the desired concentration, you need to calculate the volume of the stock solution required. The formula for dilution is:

C1V1 C2V2

Where:

C1 initial concentration (0.0171 M) V1 volume of stock solution needed C2 final concentration (C? 0.01 M for the desired 50 mL flask) V2 final volume (50 mL)

Solving for V1:

V1 (C2V2) / C1

Plugging in the values:

V1 (0.01 M × 50 mL) / 0.0171 M ≈ 29.23 mL

Therefore, you need approximately 29.23 mL of the 1000 ppm stock solution.

Step 4: Perform the Dilution

Measure 29.23 mL of the 1000 ppm stock solution and transfer it to a clean 50 mL volumetric flask. Then, add distilled water up to the calibration mark to make the final volume 50 mL. Gently swirl the flask to mix the solution thoroughly.

Step 5: Verify the Concentration

Before using the diluted solution, it is advisable to measure the concentration using an analytical method such as titration or spectrophotometry to ensure the accuracy of the dilution.

Additional Tips for Accurate Dilution

Use accurate measurements: Ensure that all volumetric glassware is clean and calibrated to avoid errors. Controlled environment: Perform the dilution in a fume hood if the solute is volatile or toxic. Consistent conditions: Maintain constant environmental conditions to ensure repeatability.

Conclusion

Diluting a 1000 ppm stock solution to a 0.01 M concentration in a 50 mL flask requires careful calculation and precise measurements. Understanding the terms and using the appropriate formulas will help you achieve the desired concentration accurately.

Key Takeaways:

Molarity and ppm are units used to express solution concentration. Calculate the molar mass of the solute to convert between ppm and molarity. Use the dilution formula to determine the volume of stock solution needed. Perform accurate measurements and verify the concentration to ensure accuracy.

For more information on solution preparation and concentration calculations, refer to standard laboratory manuals or online resources dedicated to analytical chemistry.