How to Prepare a 5% Mass/Mass (m/m) Aqueous Solution of Hydrochloric Acid (HCl)

In this guide, we will walk you through the process of making a 5% m/m aqueous solution of hydrochloric acid (HCl). This solution is commonly used in various chemical experiments and applications, particularly in laboratories and industrial settings.

What is a 5% m/m Aqueous Solution of HCl?

A 5% m/m aqueous solution of HCl (hydrochloric acid) is a solution where 5 grams of HCl is dissolved in 95 grams of water to make a total of 100 grams of solution. This concentration is typically expressed as 5 m/m, which stands for 5 grams of solute per 100 grams of solution.

Required Materials and Equipment

HCl solution: You will need a concentrated HCl solution. A 10.0 M solution is preferable but any concentration over 2.0 M can be used. Burette: To accurately measure the volume of HCL solution needed. Tared beaker: To hold the final solution and be accurately weighed. Pipette or graduated cylinder: For transferring distilled water. Distilled water: For diluting the concentrated HCL solution.

Step-by-Step Guide

Step 1: Calculate the Volume of HCl Solution Required

The first step is to calculate the volume of the concentrated HCl solution needed to obtain the desired amount of HCl. The molar mass of HCl is 36.5 g/mol. For a 10.0 M HCl solution:

1.0 L or 1000 mL of 10.0 M HCl solution contains 10 moles of HCl, which is equivalent to 365 grams (36.5 g/mol * 10 mol).

To obtain 5 grams of HCl, you would need:

Volume 5 g / 365 g/L 13.7 mL

Step 2: Measure the HCl Solution

Using a burette, accurately transfer 13.7 mL of the 10.0 M HCl solution into a tared beaker. Make sure to use the burette to achieve precise volume measurements.

Step 3: Add Distilled Water

Add distilled water to the beaker containing the 13.7 mL of HCl solution until the total mass of the solution is 100 grams. This can be done while carefully weighing the beaker during the addition of water.

Step 4: Stir the Solution

Mix the solution thoroughly to ensure that the HCl is well-dissolved.

Advanced Notes and Considerations

Using Different Concentrations: If you do not have a 10.0 M HCl solution, you can still use a higher concentration like 5.0 M or even 2.0 M. Simply adjust the volume of the solution using the same dilution principle:

Volume of concentrated HCl (Desired grams of HCl / (Molarity of concentrated HCl * Molar mass of HCl))

Concentration Variation: If a 5% m/m HCl solution is insufficient, you can increase the concentration by using a stronger HCl solution or by adjusting the volume ratio in the same manner.

Handling Safety: Hydrochloric acid is highly corrosive. Always wear appropriate protective gear, such as gloves and goggles, and work in a well-ventilated area. Ensure that you are familiar with the safety data sheet (SDS) of HCl before handling it.

Conclusion

By following the steps outlined in this guide, you can prepare a 5% m/m aqueous solution of hydrochloric acid accurately and efficiently. This solution is invaluable in numerous chemical experiments and industrial processes, providing a precise and reliable starting point for your experiments.