Preparation of a 0.5 M Nitric Acid Solution from Concentrated HNO?
Introduction
Preparation of solutions from concentrated acids, particularly strong acids like nitric acid (HNO?), requires careful handling to ensure safety and accuracy. This guide will walk you through the process of preparing 250 cm3 of a 0.5 molar (M) nitric acid solution from concentrated HNO?. Proper technique is crucial to ensure the solution's concentration is accurate and safe to work with.
Understanding the Molarity Concept
Molarity (M) is a measure of the concentration of a solution, defined as the number of moles of solute per liter of solution. When preparing solutions from concentrated acids, it's essential to use the correct molarity conversions and techniques to achieve the desired concentration.
Calculation and Preparation Steps
Let's start with the information provided:
Concentrated HNO?: molarity 15.8 M. Desired solution: Volume (V?) 250 cm3 or 0.25 L, Molarity (M?) 0.5 M.Calculation of Volume of Concentrated HNO? Needed
To calculate the volume of concentrated HNO? needed, we use the formula:
M?V? M?V?
Where:
M? 15.8 M (molarity of the concentrated HNO?) V? volume of concentrated HNO? required (in liters) M? 0.5 M (molarity of the desired solution) V? 0.25 L (volume of the desired solution)Plugging in the values:
V? (M?V?) / M? (0.5 M × 0.25 L) / 15.8 M ≈ 0.00791 L 7.91 mL
Proper Technique for Preparation
It is a good practice to add an amount of water to the container, add the concentrated acid slowly, and then add more water to reach the desired volume. This technique not only ensures that the acid is safely added but also helps in preventing any exothermic reaction that might occur, leading to a safer and more accurate preparation.
Although sulfuric acid is often discussed in this context, similar caution is advised when handling concentrated nitric acid. Always wear appropriate personal protective equipment (PPE), such as gloves and goggles, and ensure proper ventilation.
Additional Calculations and Considerations
For a more detailed calculation, let's consider another example:
Molarity of concentrated nitric acid 16 M
Given:
M? 16 M (initial concentration) M? 0.5 M (final concentration) V? 250 mL (final volume)Using the same formula:
V? (M?V?) / M? (0.5 M × 0.25 L) / 16 M 0.008 L 8 mL
This tells us that 8 mL of concentrated nitric acid is needed, which should be slowly added to a volumetric flask containing approximately 242 mL of water. The solution should then be mixed thoroughly and allowed to cool to room temperature before the volumetric flask is filled to the mark. Finally, the mixture should be shaken well to ensure uniformity.
Concluding Remarks
Preparation of a 0.5 M solution from concentrated nitric acid is a straightforward process once you understand the concept of molarity and the necessary calculations. By following these steps and taking appropriate safety precautions, you can prepare an accurate and safe solution for your experiments or laboratory work.