Solution Preparation

Summary

In this video, we demonstrate the process of preparing a standard ammonium sulfate solution for redox titrations. The procedure involves accurately weighing 1.00 grams of ammonium sulfate, dissolving it in distilled water, and transferring it to a 100 mL volumetric flask. The solution is carefully mixed and adjusted to the exact 100 mL mark using the meniscus for precision. Key steps include rinsing, careful pouring, and proper mixing techniques to ensure an accurate and homogeneous solution, essential for successful titration experiments.

Takeaways

• 😀 Use a 100 mL volumetric flask for preparing the standard solution of iron to ammonium sulfate for redox titrations.
• 😀 Accurately weigh the iron to ammonium sulfate solid, targeting a mass of 1.00 grams for the solution.
• 😀 Always tear the scale to zero before weighing the solid to avoid including the mass of the weigh boat.
• 😀 When adding solid, use a scoopula to carefully transfer the material to the weigh boat, avoiding spills or contamination of the scale.
• 😀 Do not pour the solid directly into the volumetric flask's narrow neck to prevent clogs—use a beaker for the initial dissolution.
• 😀 Rinse the weigh boat and the transfer beaker with distilled water to ensure that all solid material is transferred to the beaker.
• 😀 Stir the mixture gently and add a small amount of water to help the solid dissolve, ensuring that only 15-20% of the final volume is used in the first dissolution.
• 😀 When transferring the solution to the volumetric flask, use a funnel and a rubber policeman to prevent spills and ensure complete transfer of the solution.
• 😀 Adjust the final volume of the solution carefully, making sure the meniscus is exactly at the 100 mL mark when viewed at eye level.
• 😀 To mix the solution effectively, invert the volumetric flask at least seven times to ensure proper mixing without introducing air bubbles.

Q & A

What is the purpose of creating a standard solution in this experiment?

The purpose is to prepare ammonium sulfate as a primary standard for redox titrations, ensuring precise and accurate measurements during the titration process.

Why is ammonium sulfate chosen as the primary standard in this experiment?

Ammonium sulfate is commonly used as a primary standard because it is stable, has a known and consistent composition, and can be easily measured for accurate preparation of a solution.

How do you ensure accuracy when weighing out the solid for the solution?

Accuracy is ensured by taring the scale before weighing the solid, carefully adding the solid in small amounts, and avoiding overfilling. Any excess solid is discarded in a waste container.

Why is it important not to pour the solid directly into the volumetric flask?

The neck of the volumetric flask is narrow, and the solid could get stuck, preventing it from dissolving properly. Instead, the solid is mixed in a beaker and then transferred to the flask.

What is the purpose of using a rubber policeman when transferring the dissolved solid to the volumetric flask?

The rubber policeman helps guide the liquid from the beaker into the funnel, preventing splashing or spillage, and ensures all the liquid adheres to the beaker for accurate transfer.

Why do you need to rinse the beaker and funnel during the preparation of the solution?

Rinsing ensures that no solid or liquid remains behind, ensuring that all of the solid is transferred into the volumetric flask for accurate solution preparation.

How much water should be used initially to dissolve the solid in the beaker?

About 15 to 20 percent of the final flask volume (20 mL for a 100 mL flask) is used initially to dissolve the solid, as this amount is sufficient for dissolving most of the solid without exceeding the flask's capacity.

What is the role of distilled water in the preparation of the standard solution?

Distilled water is used to dissolve the solid and to rinse the beaker, funnel, and stir rod to ensure no solid is left behind and to accurately fill the volumetric flask to its calibration line.

Why is parallax an issue when filling the volumetric flask, and how can it be avoided?

Parallax occurs when the observer's eye is not level with the meniscus, leading to inaccurate readings. It can be avoided by ensuring the eye is directly level with the line to accurately determine the correct volume.

How do you properly mix the solution in the volumetric flask after filling it to the line?

The solution is mixed by inverting the flask several times (typically seven), as this allows the air bubble at the top to move through the solution, ensuring thorough mixing without shaking.