Preparing 0.2 M Phosphoric Acid: A Comprehensive Guide

Phosphoric acid (H3PO4) is a widely used chemical in various industries, from food processing to pharmaceuticals. Extending its applications, preparing a 0.2 M solution of phosphoric acid requires precision and a step-by-step approach, combining both chemistry and safety measures. This article provides detailed instructions on how to prepare this solution, including the necessary materials, steps, and safety precautions.

Materials Needed

To prepare a 0.2 M solution of phosphoric acid, the following materials are required:

Phosphoric acid concentrated, typically around 85% concentration. Distilled water, for dilution. Volumetric flask, to accurately measure the final volume. Pipette or graduated cylinder, for measuring the concentrated acid. Protective gear, including gloves, goggles, and a lab coat.

Steps to Prepare 0.2 M Phosphoric Acid

Step 1: Calculate the Amount of Concentrated Phosphoric Acid Needed

The first step involves determining the molarity of the concentrated phosphoric acid.

1. Determine the molarity of the concentrated phosphoric acid. For an 85% phosphoric acid solution, the density is approximately 1.685 g/mL, and the molar mass of H3PO4 is about 98 g/mol.

2. Calculate the number of moles in 1 liter of the concentrated solution:

eterangan{Mass of H3PO4 in 1 L} 85 g from 100 g of solution

tion{Moles of H3PO4} frac{85 g}{98 g/mol} approx 0.867 mol

3. Therefore, the concentration of the concentrated solution is approximately 0.867 M.

Step 2: Determine the Volume of Concentrated Acid Needed

To make 1 liter of a 0.2 M solution:

1. Calculate the required volume of concentrated acid:

olation{Volume} frac{0.2 mol/L times 1 L}{0.867 mol/L} approx 0.230 L or 230 mL

Step 3: Perform the Dilution

To prepare the 0.2 M solution:

Measure out approximately 230 mL of the concentrated phosphoric acid using a pipette or graduated cylinder. Transfer this concentrated acid to a volumetric flask containing around 400-500 mL of distilled water. Remember to carefully add the acid to the water, not the other way around, to prevent exothermic reactions that could cause splattering. Swirl the mixture gently to ensure thorough mixing. Finally, add distilled water to the volumetric flask until the total volume reaches 1 liter.

Step 4: Label the Solution

Once the solution is prepared, clearly label the volumetric flask with the concentration (0.2 M H3PO4) and the date of preparation.

Safety Precautions

Always prioritize safety when handling concentrated acids:

Wear appropriate personal protective equipment (PPE), including gloves, goggles, and a lab coat. Work in a well-ventilated area or in a fume hood if possible. Ensure proper disposal of waste materials according to local regulations.

By following these steps and guidelines, you will have successfully prepared a 0.2 M solution of phosphoric acid. This procedure is essential for precision and accuracy in laboratory settings and other applications where controlled chemical solutions are required.