Preparation of a Molar Solution

Summary

In this instructional session, Brett learns how to prepare a copper sulfate solution using a volumetric flask. The instructor explains the steps, including measuring and dissolving 7.99 grams of copper sulfate in water, filling the flask to a precise mark, and ensuring the solution's accuracy by observing the meniscus. The process emphasizes careful measurement, thorough mixing, and maintaining correct molarity. By the end, Brett successfully prepares a 0.16 molar solution, following proper lab techniques for accurate solution preparation.

Takeaways

• 🔬 The instructor is teaching how to prepare a solution using a volumetric flask.
• ⚗️ The flask in use is a 200 mL volumetric flask, designed for precise measurement of molarity.
• 📏 The instructor emphasizes the etched mark on the flask for accuracy in volume measurement.
• 💧 The solution preparation involves filling the flask halfway with water first.
• 📊 The student calculated they needed 7.99 grams of copper sulfate for the solution.
• 🌀 After adding the sample, the student must swirl the flask to dissolve the solid.
• 👀 The bottom of the meniscus should align with the mark on the flask for accuracy.
• 🧪 The instructor advises rinsing to ensure all copper sulfate enters the solution.
• 🔄 After filling, the student is instructed to mix the solution well and check the meniscus again.
• ✅ The final concentration of the prepared copper sulfate solution is 0.16 molar.

Q & A

What is the purpose of using a volumetric flask in this experiment?

The volumetric flask is used for accurately measuring out a specific volume of solution, in this case 200 milliliters, to ensure the correct molarity of the solution.

Why is the mark on the volumetric flask important?

The mark is etched into the glass to indicate the precise level to which the flask should be filled for accurate volume measurement, which is crucial for preparing a solution with the desired molarity.

What is the first step in preparing the solution using the volumetric flask?

The first step is to fill the volumetric flask about halfway with water before adding the measured sample.

How much copper sulfate was calculated to be needed for the solution?

7.99 grams of copper sulfate was calculated to be needed.

Why is it important to swirl the flask after adding the copper sulfate?

Swirling the flask helps dissolve the copper sulfate in the water, ensuring the solution is homogeneous before filling the flask to the final volume.

What is the meniscus and how should it be read?

The meniscus is the curve at the surface of the liquid. It should be read by aligning the bottom of the meniscus with the mark on the volumetric flask for accurate measurement.

What is the final step after dissolving the copper sulfate in the water?

The final step is to fill the flask up to the etched line and mix the solution well, ensuring that the liquid level remains at the mark.

What should you do if the liquid level drops after mixing the solution?

If the liquid level drops after mixing, you should add a little more water to bring it back up to the mark.

What is the concentration of the copper sulfate solution being prepared?

The concentration of the copper sulfate solution is 0.16 M (molar).

Why is it important to rinse after adding the copper sulfate?

Rinsing ensures that all traces of copper sulfate are included in the solution, preventing any solid from sticking to the container and affecting the final concentration.