Calculating the Molarity of a 96% by Mass Sulfuric Acid Solution

Introduction

Molarity, a fundamental concept in chemistry, is crucial for understanding the concentration of solutions. This article focuses on calculating the molarity of a 96% by mass sulfuric acid solution, given its density. Correctly understanding and applying these calculations is vital for performing accurate chemical experiments and maintaining safety standards in laboratories.

Calculating Molarity: A Step-by-Step Guide

To calculate the molarity of a 96% by mass sulfuric acid solution with a density of 1.8355 g/mL, follow these steps:

Step 1: Determine the Mass of the Solution

Assume we have 1 liter (1000 mL) of the solution. Using the given density:

mass of solution 1.8355 g/mL x 1000 mL 1835.5 g

Step 2: Calculate the Mass of Sulfuric Acid in the Solution

Since the solution is 96% sulfuric acid by mass:

mass of H2SO4 0.96 x 1835.5 g 1756.64 g

Step 3: Calculate the Number of Moles of Sulfuric Acid

The molar mass of sulfuric acid (H2SO4) is approximately 98.08 g/mol. Now, calculate the number of moles:

moles of H2SO4 (1756.64 g) / (98.08 g/mol) ≈ 17.88 moles

Step 4: Calculate the Molarity of the Solution

Molarity (M) is defined as the number of moles of solute per liter of solution. Since we have 17.88 moles of sulfuric acid in 1 liter of solution, the molarity is:

molarity 17.88 moles / 1 L 17.88 M

Common Errors in Molarity Calculations

It's important to recognize common mistakes when calculating molarity. One such error could be using the wrong density value. For instance, if the density is given as 1.86 g/mL instead of 1.8355 g/mL, the result would be incorrect. The correct density is 1.8355 g/mL.

Example Problems

Example 1: 95% by Mass Sulfuric Acid Solution

For a 95% by mass sulfuric acid solution with a density of 1.84 g/mL, calculate the molarity:

Mass of the solution: 1000 mL x 1.84 g/mL 1840 g

Mass of H2SO4: 1840 g x 95% 1748 g

Moles of H2SO4: 1748 g / 98 g/mol 17.8 moles

Molarity: 17.8 moles / 1 L 17.8 M

Example 2: General Approach

To find the molarity of any sulfuric acid solution, you need the volume of the solution. Here’s the general formula:

Molarity m / (V x 1000)

Where:

m mass of solute (grams) V volume of solution (mL) 1000 conversion factor to convert mL to L

To find the moles of solute, use the formula:

Moles of solute mass of solute / molar mass of solute

Finally, molarity moles of solute / volume of solution in liters.

Conclusion

Calculating the molarity of a sulfuric acid solution involves precise calculations and attention to detail. The correct formula and density value are crucial for accurate results. Understanding these concepts ensures proper handling and application of sulfuric acid in various chemical processes and experiments.