Preparation of 2M Hydrochloric Acid (HCl) Solution from Concentrated HCl (30-34%)

To prepare a 2 M hydrochloric acid (HCl) solution from a concentrated HCl solution with a 30-34% w/w concentration, follow these detailed steps:

Step 1: Determine the Density of the Concentrated HCl Solution

The density of concentrated HCl (30-34%) is approximately 1.18 g/mL. For calculations, you may use an average density of 1.19 g/mL.

Step 2: Calculate the Molarity of the Concentrated HCl

To calculate the molarity of the concentrated HCl, first determine the mass of HCl in 1 L of the solution:

For a 30% solution: Mass of solution 1000 mL × 1.19 g/mL 1190 g Mass of HCl 0.30 × 1190 g 357 g For a 34% solution: Mass of solution 1000 mL × 1.19 g/mL 1190 g Mass of HCl 0.34 × 1190 g 404.6 g

Next, calculate the number of moles of HCl based on the molar mass (36.46 g/mol):

For 30%: Moles of HCl 357 g / 36.46 g/mol ≈ 9.79 mol For 34%: Moles of HCl 404.6 g / 36.46 g/mol ≈ 11.09 mol

Finally, calculate the molarity of the concentrated HCl:

For 30%: Molarity 9.79 mol / 1 L 9.79 M For 34%: Molarity 11.09 mol / 1 L 11.09 M

Step 3: Perform the Dilution Calculation

To prepare a 2 M solution from the concentrated solution, use the dilution formula: C1V1 C2V2:

C1 concentration of the concentrated solution (9.79 M or 11.09 M) V1 volume of the concentrated solution needed C2 desired concentration (2 M) V2 final volume of the diluted solution

Example Calculation Using 30% HCl (9.79 M):

C1 9.79 M, C2 2 M, V2 1 L V1 (2 M × 1 L) / 9.79 M ≈ 0.204 L or 204 mL

Example Calculation Using 34% HCl (11.09 M):

C1 11.09 M, C2 2 M, V2 1 L V1 (2 M × 1 L) / 11.09 M ≈ 0.180 L or 180 mL

Step 4: Prepare the Solution

Measure the calculated volume of concentrated HCl (204 mL for 30% or 180 mL for 34%).

Slowly add the concentrated HCl to a volumetric flask containing a sufficient amount of distilled water (e.g., about 500 mL initially). After adding the acid, carefully bring the total volume up to 1 L with distilled water.

Mix thoroughly and ensure the solution is homogeneous.

Safety Precautions

Always add acid to water, not water to acid, to prevent exothermic reactions that can cause splattering.

Wear appropriate personal protective equipment (gloves, goggles, lab coat) when handling concentrated acids.

This will give you a 2 M HCl solution. Adjust the calculations based on the specific concentration of your HCl solution if necessary.