Understanding Stock Solutions

Oct 13, 2025 by magicalceylontours.com 114 views

Introduction

In chemistry, a stock solution is a concentrated solution that is used as a starting point for preparing other solutions with specific concentrations. The process of dilution is a crucial step in preparing solutions with desired concentrations for various applications, including laboratory experiments, industrial processes, and quality control. In this article, we will explore the concept of a stock solution and dilution, using a specific example to illustrate the process.

Understanding Stock Solutions

A stock solution is a concentrated solution that contains a known amount of a substance, usually a solute, dissolved in a solvent. The concentration of the stock solution is typically much higher than the desired concentration of the final solution. The stock solution is then diluted to achieve the desired concentration. The process of dilution involves adding a solvent to the stock solution to reduce its concentration.

Calculating the Concentration of the Stock Solution

To calculate the concentration of the stock solution, we need to know the amount of solute (in this case, $\left( NH_4\right)_2 SO_4$ ) and the volume of the solution. The molar mass of $\left( NH_4\right)_2 SO_4$ is 132.14 g/mol. We are given that 66.05 g of $\left( NH_4\right)_2 SO_4$ is dissolved in enough water to make 250 mL of solution.

First, we need to calculate the number of moles of $\left( NH_4\right)_2 SO_4$ dissolved in the solution:

\text{Number of moles} = \frac{\text{Mass of solute}}{\text{Molar mass}}

\text{Number of moles} = \frac{66.05 \text{ g}}{132.14 \text{ g/mol}}

\text{Number of moles} = 0.500 \text{ mol}

Next, we need to calculate the concentration of the stock solution in moles per liter (M):

\text{Concentration} = \frac{\text{Number of moles}}{\text{Volume of solution (L)}}

\text{Concentration} = \frac{0.500 \text{ mol}}{0.250 \text{ L}}

\text{Concentration} = 2.00 \text{ M}

Dilution of the Stock Solution

A 10.0 mL sample of the stock solution is then diluted to 50.0 mL. To calculate the concentration of the diluted solution, we need to know the initial concentration of the stock solution and the volume of the diluted solution.

The initial concentration of the stock solution is 2.00 M, and the volume of the diluted solution is 50.0 mL. We can calculate the concentration of the diluted solution using the dilution formula:

\text{Concentration of diluted solution} = \frac{\text{Initial concentration} \times \text{Initial volume}}{\text{Final volume}}

\text{Concentration of diluted solution} = \frac{2.00 \text{ M} \times 10.0 \text{ mL}}{50.0 \text{ mL}}

\text{Concentration of diluted solution} = 0.400 \text{ M}

Conclusion

In conclusion, a stock solution is a concentrated solution that is used as a starting point for preparing other solutions with specific concentrations. The process of dilution involves adding a solvent to the stock solution to reduce its concentration. By understanding the concept of stock solutions and dilution, we can prepare solutions with desired concentrations for various applications.

Calculating the Concentration of the Diluted Solution

To calculate the concentration of the diluted solution, we need to know the initial concentration of the stock solution and the volume of the diluted solution. We can use the dilution formula to calculate the concentration of the diluted solution:

\text{Concentration of diluted solution} = \frac{\text{Initial concentration} \times \text{Initial volume}}{\text{Final volume}}

\text{Concentration of diluted solution} = \frac{2.00 \text{ M} \times 10.0 \text{ mL}}{50.0 \text{ mL}}

\text{Concentration of diluted solution} = 0.400 \text{ M}

Understanding the Concept of Molarity

Molarity is a measure of the concentration of a solution, expressed in moles of solute per liter of solution. It is an important concept in chemistry, as it allows us to calculate the concentration of a solution and predict its behavior.

Calculating the Number of Moles of Solute

To calculate the number of moles of solute, we need to know the mass of the solute and its molar mass. We can use the formula:

\text{Number of moles} = \frac{\text{Mass of solute}}{\text{Molar mass}}

\text{Number of moles} = \frac{66.05 \text{ g}}{132.14 \text{ g/mol}}

\text{Number of moles} = 0.500 \text{ mol}

Calculating the Concentration of the Stock Solution

To calculate the concentration of the stock solution, we need to know the number of moles of solute and the volume of the solution. We can use the formula:

\text{Concentration} = \frac{\text{Number of moles}}{\text{Volume of solution (L)}}

\text{Concentration} = \frac{0.500 \text{ mol}}{0.250 \text{ L}}

\text{Concentration} = 2.00 \text{ M}

Understanding the Concept of Dilution

Dilution is the process of adding a solvent to a solution to reduce its concentration. It is an important concept in chemistry, as it allows us to prepare solutions with desired concentrations for various applications.

Calculating the Concentration of the Diluted Solution

\text{Concentration of diluted solution} = \frac{\text{Initial concentration} \times \text{Initial volume}}{\text{Final volume}}

\text{Concentration of diluted solution} = \frac{2.00 \text{ M} \times 10.0 \text{ mL}}{50.0 \text{ mL}}

\text{Concentration of diluted solution} = 0.400 \text{ M}

Conclusion

References

CRC Handbook of Chemistry and Physics, 97th ed., CRC Press, 2016.
Chemistry: The Central Science, 14th ed., Prentice Hall, 2018.
Dilution and Concentration, Chemistry LibreTexts, 2020.

Glossary

Molarity: A measure of the concentration of a solution, expressed in moles of solute per liter of solution.
Stock solution: A concentrated solution that is used as a starting point for preparing other solutions with specific concentrations.
Dilution: The process of adding a solvent to a solution to reduce its concentration.
Molar mass: The mass of one mole of a substance, expressed in grams per mole.

Introduction

In our previous article, we explored the concept of a stock solution and dilution, using a specific example to illustrate the process. In this article, we will answer some frequently asked questions about stock solutions and dilution.

Q: What is a stock solution?

A: A stock solution is a concentrated solution that is used as a starting point for preparing other solutions with specific concentrations. It is typically much more concentrated than the desired final solution.

Q: Why do we need stock solutions?

A: Stock solutions are used to prepare solutions with specific concentrations for various applications, including laboratory experiments, industrial processes, and quality control. They allow us to easily prepare solutions with the desired concentration.

Q: How do we calculate the concentration of a stock solution?

A: To calculate the concentration of a stock solution, we need to know the amount of solute (in this case, $\left( NH_4\right)_2 SO_4$ ) and the volume of the solution. We can use the formula:

\text{Concentration} = \frac{\text{Number of moles}}{\text{Volume of solution (L)}}

Q: What is dilution?

A: Dilution is the process of adding a solvent to a solution to reduce its concentration. It is an important concept in chemistry, as it allows us to prepare solutions with desired concentrations for various applications.

Q: How do we calculate the concentration of a diluted solution?

A: To calculate the concentration of a diluted solution, we need to know the initial concentration of the stock solution and the volume of the diluted solution. We can use the dilution formula to calculate the concentration of the diluted solution:

\text{Concentration of diluted solution} = \frac{\text{Initial concentration} \times \text{Initial volume}}{\text{Final volume}}

Q: What is the difference between a stock solution and a diluted solution?

A: A stock solution is a concentrated solution that is used as a starting point for preparing other solutions with specific concentrations. A diluted solution is a solution that has been prepared by adding a solvent to a stock solution to reduce its concentration.

Q: Why is it important to know the concentration of a solution?

A: Knowing the concentration of a solution is important because it allows us to predict its behavior and ensure that it is safe to use. It is also important for quality control and regulatory purposes.

Q: Can I use a stock solution to prepare a solution with a different concentration?

A: Yes, you can use a stock solution to prepare a solution with a different concentration. However, you will need to calculate the new concentration using the dilution formula.

Q: How do I store a stock solution?

A: Stock solutions should be stored in a cool, dry place, away from light. They should also be labeled with the date of preparation and the concentration of the solution.

Q: Can I use a stock solution that has been stored for a long time?

A: It depends on the type of solution and the storage conditions. Some stock solutions can be stored for a long time, while others may degrade over time. It is always best to check the solution before using it.

Q: How do I dispose of a stock solution?

A: Stock solutions should be disposed of according to local regulations and guidelines. They should be handled and disposed of in a way that minimizes exposure to the environment and human health.

Conclusion

References

CRC Handbook of Chemistry and Physics, 97th ed., CRC Press, 2016.
Chemistry: The Central Science, 14th ed., Prentice Hall, 2018.
Dilution and Concentration, Chemistry LibreTexts, 2020.

Glossary

Molarity: A measure of the concentration of a solution, expressed in moles of solute per liter of solution.
Stock solution: A concentrated solution that is used as a starting point for preparing other solutions with specific concentrations.
Dilution: The process of adding a solvent to a solution to reduce its concentration.
Molar mass: The mass of one mole of a substance, expressed in grams per mole.