Question

How do I make different pH solutions of 3 mg/L from the 10mg/L stock solution using (HCL and NaCl) pH 3,4,5,6..9?

Answer 1

To prepare different pH solutions using hydrochloric acid (HCl) and sodium hydroxide (NaOH) from a stock solution of 10 mg/L, you can follow these steps:

1. Prepare the stock solution: Start with a stock solution of 10 mg/L. This solution will serve as the starting point for preparing solutions of different pH levels.

2. Determine the required volume: Calculate the volume of the stock solution needed to achieve the desired concentration in the final solution. For example, if you want to prepare a 1 L solution, you would need 1 L of the stock solution for a final concentration of 3 mg/L.

3. Adjust the pH using HCl and NaOH: To adjust the pH, you will use hydrochloric acid (HCl) to lower the pH and sodium hydroxide (NaOH) to raise the pH. The specific volumes of HCl and NaOH required will depend on the target pH and the starting pH of the stock solution.

   • pH 3-6 (Acidic range): To lower the pH from 10 to the desired level, add HCl dropwise while monitoring the pH using a pH meter or indicator paper. Start with a small volume (e.g., 1 mL) of HCl, mix well, and measure the pH. Repeat this process until the desired pH is reached. If the pH overshoots, you can raise it by adding small volumes of NaOH dropwise.

   • pH 7 (Neutral): Since the stock solution is already acidic, you can directly dilute it with deionized water to achieve the desired concentration while maintaining a neutral pH of 7.

   • pH 8-9 (Basic range): To raise the pH from 10 to the desired level, add NaOH dropwise while monitoring the pH. Again, start with a small volume of NaOH (e.g., 1 mL), mix well, and measure the pH. Repeat this process until the desired pH is reached. If the pH overshoots, you can lower it by adding small volumes of HCl dropwise.

4. Dilute to the final volume: Once you have adjusted the pH to the desired level, dilute the solution with deionized water to the final volume (e.g., 1 L).

Remember to handle acids and bases with proper safety precautions and use appropriate laboratory techniques and equipment. It is recommended to have a pH meter or pH indicator paper to accurately measure and adjust the pH of the solutions.