91Ó°ÊÓ

Milliequivalents (meq) are a unit of chemical measurement commonly used in calculations involving acids and bases. They are useful because they help standardize measurements based on the number of reactive units in a substance, rather than the amount of the substance itself. This is important in chemistry when dealing with reactions or solutions.

To calculate milliequivalents, you multiply the normality of the solution (\(N\), which is the equivalent concentration of solute per liter of solution) by the volume of the solution in milliliters (\(V\)).
This gives us the equation: \( \text{meq} = N \times V \).

• Normality (\(N\)) refers to the concentration of equivalents per liter of solution.
• Volume (\(V\)) is the amount of the solution in milliliters.

By using milliequivalents, you are essentially counting how many reactive units are present, which is useful for determining the outcome of reactions or the strength of a solution. In our exercise, we use this method to assess the contributions of different acids in a mixture.

When you mix different acids, you're bringing together solutions with varied characteristics. In the exercise, we're tasked with mixing hydrochloric acid, sulphuric acid, and nitric acid.
Each of these acids has its own normality and volume, and this affects the final composition of the mixture.
To understand the process:

• Hydrochloric acid (\(HCl\)): Starts with a normality of 0.5N and a volume of 20 mL, giving 10 meq.
• Sulphuric acid (\(H_2SO_4\)): Has a normality of 0.1N and a volume of 60 mL, contributing 6 meq.
• Nitric acid (\(HNO_3\)): With a normality of 0.2N and a larger volume of 150 mL, adds 30 meq to the mixture.

When these acids are combined, the total milliequivalents are calculated by summing up the contributions from each acid.
This results in a total of 46 meq. The total volume of the mixture is the sum of the individual volumes: 230 mL.

To determine the normality of an acid mixture, follow a systematic step-by-step approach. This ensures accuracy and avoids confusion. Here's how it's done:

• Calculate Milliequivalents for Each Acid: Using the formula \( \text{meq} = N \times V \), find the milliequivalents for each component in the mixture. This turns individual normality and volume into a comparable unit across all components.
• Find Total Milliequivalents: Add up the milliequivalents you've calculated for each acid. This total represents the overall reactive capacity of the mixture.
• Calculate Total Volume: Add the volumes of the individual acids to find the complete volume of the mixture.
• Determine the Mixture's Normality: With total milliequivalents and total volume, calculate the final normality using \( N = \frac{\text{Total meq}}{V_{\text{total}}} \). Substitute the known values to find the normality.

In our case, substituting 46 total meq and 230 mL volume into this formula gives a normality of 0.2N.
This step-by-step method not only helps find the answer accurately but also aids in understanding the roles different variables play in the calculation.