How to Safely Prepare 3M HCl Solution from 37% HCl- A Step-by-Step Guide

How to Prepare 3M HCl from 37% HCl

Preparing a 3M (molar) solution of hydrochloric acid (HCl) from a 37% (w/w) concentrated solution is a common laboratory task. This process involves diluting the concentrated acid to achieve the desired concentration. Here’s a step-by-step guide on how to prepare 3M HCl from 37% HCl.

Materials Needed:

– 37% hydrochloric acid solution
– Distilled water
– A graduated cylinder or pipette
– A container with a tight-fitting lid
– Safety equipment (gloves, goggles, lab coat)

Step 1: Calculate the Volume of 37% HCl Needed

First, determine the volume of the 37% HCl solution required to prepare 1 liter of 3M HCl. The molarity (M) of a solution is calculated using the formula:

M = (Moles of solute) / (Volume of solution in liters)

To find the moles of HCl needed for a 3M solution, use the formula:

Moles of HCl = Molarity × Volume of solution in liters × Molar mass of HCl

The molar mass of HCl is approximately 36.46 g/mol. For a 3M solution, you need:

Moles of HCl = 3 M × 1 L × 36.46 g/mol = 108.38 g

Now, convert the mass of HCl to volume using the density of the 37% HCl solution, which is approximately 1.18 g/mL:

Volume of 37% HCl = (108.38 g) / (1.18 g/mL) ≈ 91.9 mL

So, you need approximately 91.9 mL of the 37% HCl solution to prepare 1 liter of 3M HCl.

Step 2: Prepare the Solution

1. Wear appropriate safety equipment (gloves, goggles, and lab coat) before starting the procedure.
2. Using a graduated cylinder or pipette, measure out 91.9 mL of the 37% HCl solution.
3. Pour the measured 37% HCl into a container with a tight-fitting lid.
4. Add distilled water to the container while stirring gently. Add water slowly to avoid generating excessive heat, which can cause the solution to splash or boil.
5. Once the total volume reaches 1 liter, stop adding water and ensure the solution is well-mixed.

Step 3: Final Check

After preparing the 3M HCl solution, it’s essential to verify the concentration using a pH meter or a standardized titration method. Adjust the concentration if necessary by adding more 37% HCl or distilled water.

Conclusion

Preparing 3M HCl from 37% HCl involves diluting the concentrated acid with distilled water. Always follow proper safety procedures and ensure that the final solution is well-mixed and accurately measured. With this guide, you can successfully prepare the desired concentration of HCl for your laboratory needs.