Preparing a 0.1 N Hydrochloric Acid (HCl) Solution from a 37% W/W Concentrate: A Comprehensive Guide

In industrial and laboratory settings, preparing specific concentrations of hydrochloric acid (HCl) solutions from concentrated stocks is a common procedure. This guide will walk you through the process of preparing a 0.1 N HCl solution from a 37% w/w HCl solution. This detailed step-by-step procedure adheres to proper safety protocols and ensures accurate concentration preparation.

Understanding the Concentration of the Stock Solution

First, it is crucial to understand the concentration and density of the stock solution you are working with. For a 37% w/w HCl solution:

Density of 37 HCl

The density of concentrated HCl is approximately 1.19 g/mL.

Calculate the Mass of HCl in 1 L of Concentrated Solution

Use the following calculations to determine the mass of HCl in 1 L of the concentrated solution:

Mass of Solution: Mass of solution Density * Volume 1.19 g/mL * 1000 mL 1190 g Mass of HCl: Mass of HCl 37% * 1190 g 0.37 * 1190 g ≈ 440.3 g

Calculate the Number of Moles of HCl

The molar mass of HCl is 36.46 g/mol.

Moles of HCl: Moles of HCl Mass of HCl / Molar mass of HCl 440.3 g / 36.46 g/mol ≈ 12.08 mol

Calculate the Normality of the Stock Solution

HCl is a monoprotic acid, so its normality (N) is equal to its molarity (M). Given that the volume of the concentrated solution is 1 L:

Normality of Concentrated HCl: Normality 12.08 N

Use the Dilution Equation

To prepare a 0.1 N solution, use the dilution formula:

C1V1 C2V2
C1 Initial concentration (12.08 N)
V1 Volume of concentrated solution to use (unknown)
C2 Final concentration (0.1 N)
V2 Final volume of diluted solution (desired volume)

Assuming you want to prepare 1 L (1000 mL) of 0.1 N solution:

12.08 N * V1 0.1 N * 1000 mL
V1 (0.1 * 1000 mL) / 12.08 ≈ 8.28 mL

Prepare the Solution

Follow these steps to prepare the desired solution:

Measure 8.28 mL of 37% HCl: Use a pipette or a graduated cylinder to accurately measure this volume. Dilute it with distilled water: Transfer the measured HCl into a volumetric flask or a suitable container. Add distilled water while stirring gently to ensure complete dissolution. Add water to reach a final volume of 1 L: Use a flask or a container with a mark for 1 L, and carefully add water until the meniscus reaches the mark.

Always add acid to water instead of water to acid to prevent boiling and potential splash hazards. Safety equipment such as gloves and goggles should be worn during the entire preparation process.

Summary

This guide provides a comprehensive procedure for preparing a 0.1 N HCl solution from a 37% w/w HCl concentrate. By following these steps accurately and safely, you can ensure the correct concentration is achieved in your laboratory or industrial setting.