Padronização de solução (parte 1 - experimento): titulação de hidróxido de sódio (NaOH)

Summary

In this chemistry tutorial, the instructor demonstrates how to standardize a sodium hydroxide (NaOH) solution using potassium hydrogen phthalate (KHP) as a primary standard. The process involves accurately weighing KHP, dissolving it in distilled water, and titrating with NaOH while using phenolphthalein as an indicator. The titration continues until the solution turns light pink, signaling the endpoint. The final volume of NaOH used is measured to calculate its true concentration. This step-by-step guide is ideal for learners interested in the practical aspects of solution preparation and titration techniques.

Takeaways

• 😀 Introduction to the experiment: The goal is to standardize a sodium hydroxide (NaOH) solution using potassium hydrogen phthalate (KHP).
• 😀 Padronization involves determining if the NaOH solution has the expected concentration of 0.1 mol/L, which can vary slightly due to preparation errors.
• 😀 A primary standard, KHP, is used because it's pure and stable, essential for accurately determining NaOH concentration.
• 😀 KHP is weighed carefully (about 0.4 grams), and the tare function of the balance is used to exclude the weight of the container.
• 😀 The KHP is dissolved in distilled water, and it’s important to ensure all solid is fully dissolved before proceeding.
• 😀 Phenolphthalein, a pH indicator, is added to the KHP solution. It helps identify when the titration reaches its endpoint by changing color.
• 😀 The NaOH solution is prepared and filled into a burette. The burette should be free from air bubbles for accurate measurement.
• 😀 The titration is performed by slowly adding NaOH drop by drop to the KHP solution, agitating constantly to ensure proper mixing.
• 😀 The endpoint of the titration is reached when the solution changes from colorless to a faint pink, indicating neutralization.
• 😀 After titration, the volume of NaOH used is recorded. The concentration of NaOH is then calculated using this volume and the mass of KHP used in the reaction.

Q & A

What is the main goal of the experiment described in the video?

The main goal of the experiment is to standardize a sodium hydroxide (NaOH) solution to determine its actual concentration, which is initially assumed to be 0.1 mol/L.

Why is standardization of the sodium hydroxide solution necessary?

Standardization is necessary because the actual concentration of the NaOH solution may vary due to human error in preparing the solution, differences in volume measurements, or inaccuracies in the glassware, and we need to determine the exact concentration for precise calculations in future experiments.

What substance is used as the primary reagent for the standardization?

The primary reagent used for the standardization is potassium biftalate (KHP), which is a pure substance that reacts with sodium hydroxide in the titration process.

What is the purpose of using potassium biftalate in the experiment?

Potassium biftalate is used as a primary standard because it reacts in a known stoichiometric relationship with sodium hydroxide, allowing the calculation of the NaOH solution's concentration.

What equipment is used to measure the volume of the sodium hydroxide solution?

A burette is used to measure the volume of the sodium hydroxide solution during the titration process.

What role does phenolphthalein play in the experiment?

Phenolphthalein is used as an indicator in the titration. It changes color to indicate the endpoint of the reaction, signaling when all the potassium biftalate has reacted with the sodium hydroxide.

Why is it important to avoid air bubbles in the burette?

Air bubbles in the burette can lead to inaccurate volume measurements, as they would result in an incorrect reading of the volume of the sodium hydroxide solution used in the titration.

How should the titration be conducted to avoid errors in the color change?

The titration should be conducted slowly, adding the sodium hydroxide solution drop by drop, and the solution in the Erlenmeyer flask should be constantly stirred to ensure accurate detection of the color change at the endpoint.

What is the correct color change to indicate the completion of the titration?

The correct color change is a light pink color that remains stable, indicating that the sodium hydroxide has completely neutralized the potassium biftalate.

What happens if too much sodium hydroxide is added during the titration?

If too much sodium hydroxide is added, the solution will turn a darker pink, indicating an overshoot past the endpoint, which could lead to inaccurate results in determining the concentration of the NaOH solution.