Calculate the number of moles of calcium sulfate

Oct 13, 2025 by wbrum.org 29 views

Introduction

In chemistry, preparing solutions with precise concentrations is crucial for various experiments and applications. A chemist prepares a solution of calcium sulfate (CaSO4) by measuring out 5.1 mg of calcium sulfate into a 250. mL volumetric flask and filling the flask to the mark with water. To determine the concentration of this solution in mol/L, we need to perform a series of calculations.

Understanding the Problem

The chemist has prepared a solution with a known mass of calcium sulfate (5.1 mg) in a known volume of water (250. mL). To calculate the concentration of the solution in mol/L, we need to follow these steps:

Determine the molar mass of calcium sulfate (CaSO4): The molar mass of CaSO4 is the sum of the atomic masses of calcium (Ca), sulfur (S), and four oxygen (O) atoms.
Calculate the number of moles of calcium sulfate: Using the molar mass of CaSO4, we can calculate the number of moles of calcium sulfate present in the solution.
Calculate the concentration of the solution in mol/L: We will use the number of moles of calcium sulfate and the volume of the solution (250. mL) to calculate the concentration in mol/L.

Calculating the Molar Mass of Calcium Sulfate (CaSO4)

The atomic masses of the elements involved are:

Calcium (Ca): 40.08 g/mol
Sulfur (S): 32.07 g/mol
Oxygen (O): 16.00 g/mol

The molar mass of CaSO4 is the sum of the atomic masses of these elements:

Molar mass of CaSO4 = 40.08 g/mol (Ca) + 32.07 g/mol (S) + 4 × 16.00 g/mol (O) Molar mass of CaSO4 = 40.08 g/mol + 32.07 g/mol + 64.00 g/mol Molar mass of CaSO4 = 136.15 g/mol

Calculating the Number of Moles of Calcium Sulfate

To calculate the number of moles of calcium sulfate, we need to divide the mass of calcium sulfate (5.1 mg) by its molar mass (136.15 g/mol).

First, we need to convert the mass of calcium sulfate from milligrams (mg) to grams (g):

5.1 mg = 0.0051 g

Now, we can calculate the number of moles of calcium sulfate:

Number of moles = mass of CaSO4 (g) / molar mass of CaSO4 (g/mol) Number of moles = 0.0051 g / 136.15 g/mol Number of moles ≈ 3.74 × 10^(-5) mol

Calculating the Concentration of the Solution in Mol/L

To calculate the concentration of the solution in mol/L, we need to divide the number of moles of calcium sulfate by the volume of the solution (250. mL).

First, we need to convert the volume of the solution from milliliters (mL) to liters (L):

mL = 0.250 L

Now, we can calculate the concentration of the solution:

Concentration (mol/L) = number of moles / volume of solution (L) Concentration (mol/L) = 3.74 × 10^(-5) mol / 0.250 L Concentration (mol/L) ≈ 1.50 × 10^(-4) mol/L

Conclusion

In this article, we have calculated the concentration of a chemist's solution of calcium sulfate (CaSO4) in mol/L. We started by determining the molar mass of CaSO4, then calculated the number of moles of calcium sulfate present in the solution, and finally calculated the concentration of the solution in mol/L. The concentration of the solution is approximately 1.50 × 10^(-4) mol/L.

Discussion

The concentration of a solution is a critical parameter in chemistry, and accurate calculations are essential for various experiments and applications. In this article, we have demonstrated the importance of precise calculations in determining the concentration of a solution. By following the steps outlined in this article, chemists and students can calculate the concentration of a solution with confidence.

Future Directions

In the future, we can explore other aspects of solution chemistry, such as calculating the concentration of a solution with a known volume and unknown mass, or determining the molar mass of a compound with a known concentration and volume. These calculations will require a deeper understanding of chemistry and mathematical concepts, but will provide valuable insights into the world of solution chemistry.

References

CRC Handbook of Chemistry and Physics, 97th Edition
IUPAC Compendium of Chemical Terminology, 2nd Edition
Chemistry: An Atoms First Approach, 2nd Edition by Steven S. Zumdahl

Introduction

In our previous article, we calculated the concentration of a chemist's solution of calcium sulfate (CaSO4) in mol/L. In this article, we will address some common questions and concerns related to calculating concentration.

Q: What is the importance of calculating concentration in chemistry?

A: Calculating concentration is crucial in chemistry as it helps us understand the amount of substance present in a given volume of a solution. This information is essential for various experiments and applications, such as determining the amount of reactants needed for a reaction, understanding the behavior of solutions, and predicting the outcomes of chemical reactions.

Q: How do I calculate the concentration of a solution if I know the mass of the solute and the volume of the solution?

A: To calculate the concentration of a solution, you need to follow these steps:

Determine the molar mass of the solute.
Calculate the number of moles of the solute using the mass of the solute and its molar mass.
Calculate the concentration of the solution by dividing the number of moles of the solute by the volume of the solution.

Q: What is the difference between molarity and molality?

A: Molarity and molality are two different units of concentration. Molarity is defined as the number of moles of solute per liter of solution, while molality is defined as the number of moles of solute per kilogram of solvent.

Q: How do I convert between molarity and molality?

A: To convert between molarity and molality, you need to know the density of the solution. The conversion factor is:

Molarity (M) = molality (m) × density (ρ)

Q: What is the significance of the molar mass of a substance?

A: The molar mass of a substance is the sum of the atomic masses of its constituent atoms. It is an essential parameter in chemistry as it helps us calculate the number of moles of a substance and its concentration in a solution.

Q: How do I determine the molar mass of a substance?

A: To determine the molar mass of a substance, you need to know the atomic masses of its constituent atoms. You can find this information in a periodic table or a reference book.

Q: What is the difference between a strong acid and a weak acid?

A: A strong acid is an acid that completely dissociates in water, while a weak acid is an acid that only partially dissociates in water.

Q: How do I calculate the pH of a solution?

A: To calculate the pH of a solution, you need to know the concentration of hydrogen ions (H+) in the solution. The pH is defined as the negative logarithm of the concentration of hydrogen ions:

pH = -log[H+]

Q: What is the significance of the pH scale?

A: The pH scale is a measure of the acidity or basicity of a solution. It ranges from 0 to 14, with a pH of 7 being neutral, a pH less than 7 being acidic, and a pH greater than 7 being basic.

Conclusion

In this article, we have addressed some common questions and concerns related to calculating concentration. We have discussed the importance of calculating concentration, the difference between molarity and molality, and the significance of the molar mass of a substance. We have also provided information on how to calculate the pH of a solution and the significance of the pH scale.

Discussion

Calculating concentration is a critical aspect of chemistry, and accurate calculations are essential for various experiments and applications. In this article, we have demonstrated the importance of understanding the concepts of concentration, molarity, and molality. By following the steps outlined in this article, chemists and students can calculate the concentration of a solution with confidence.

Future Directions

References

CRC Handbook of Chemistry and Physics, 97th Edition
IUPAC Compendium of Chemical Terminology, 2nd Edition
Chemistry: An Atoms First Approach, 2nd Edition by Steven S. Zumdahl