Calculating Moles of Sulfuric Acid to Prepare a Solution

In chemistry, determining the number of moles of a substance required to prepare a solution is a fundamental skill. For instance, to find how many moles of H2SO4 (sulfuric acid) are needed to prepare 200 mL of a 1.0 M solution, you can follow a straightforward process involving molarity, volume, and moles. This article will guide you through the steps and provide a comprehensive understanding of the concept.

Basics of Molarity and Moles

Molarity (M) is defined as the number of moles of solute per liter of solution. The formula for calculating molarity is:

Molarity (M) Moles of Solute / Volume of Solution (in liters)

Example Calculation: 200 mL of 1.0 M H2SO4 Solution

To prepare 200 mL of a 1.0 M solution of sulfuric acid, follow these steps:

Convert the volume from milliliters to liters:

200 mL 0.200 L

Use the formula to calculate the moles:

Moles Molarity × Volume in liters

Moles 1.0 M × 0.200 L 0.200 moles

Therefore, you need 0.200 moles of H2SO4 to prepare 200 mL of a 1.0 M solution.

Understanding the Molar Expression

The molar concentration (M) is given by the equation:

M n/V

where n is the number of moles of solute and V is the volume of the solution in liters. This expression allows us to determine the moles of solute:

Moles (n) Molarity (M) × Volume (V in liters)

Using the given values:

Moles of H2SO4 1.0 M × 0.2 L 0.2 moles

This molar quantity refers to sulfuric acid, a diprotic acid, which plays a crucial role in various industrial and laboratory applications.

Demoivre's Formula and Dilution

The technique demonstrated in this example is known as dilution. The formula M1V1 M2V2 is used to calculate the volume of the concentrated acid needed to prepare the desired solution.

Example of Using M1V1 M2V2

Suppose you have a concentrated sulfuric acid solution that is 12 M, and you need to prepare 3.00 liters of a 4.0 M solution. You can use the formula M1V1 M2V2 to find the initial volume (V1) of the concentrated acid needed:

Rearrange the formula to solve for V1:

V1 (M2V2) / M1

Plug in the values:

V1 (4.0 M × 3.00 L) / 12 M 0.67 L

This means that you need 0.67 liters (or 670 mL) of the original 12 M concentrated sulfuric acid solution. The remaining volume (2.33 liters) should be made up with distilled water to achieve the final volume of 3.00 liters.

Conclusion

Understanding and applying the concept of molarity and moles is essential in chemistry. The steps outlined above can be generalized to calculate the number of moles required to prepare various solutions. By mastering these techniques, chemists can effectively conduct experiments and prepare solutions for different applications. Whether you're in a laboratory or dealing with industrial processes, the principles of molarity and dilution are valuable knowledge.