2024 WAEC CHEMISTRY PRACTICAL REDOX TITRATION (final hints)

Summary

In this comprehensive video from the 300 Plus Academy, the focus is on volumetric analysis, also known as quantitative analysis, for final exam revision. The presenter discusses the nuances of a non-conventional acid-based titration involving potassium permanganate and iron(II) sulfate. The video provides a detailed explanation of the color change that indicates the end point of the titration, the importance of acidifying the solution to preserve iron(II) ions, and the economic rationale behind this step. The presenter also guides viewers through the titration procedure, the construction of a titration table, and the calculations required to determine the concentration of the solutions involved. The video concludes with a confident assertion that the topics covered are highly likely to appear in the upcoming exams, encouraging students to prepare diligently for their chemistry practicals.

Takeaways

• 📚 The lecture focuses on volumetric analysis, also known as quantitative analysis, for final revision with a focus on titration methods.
• 🔍 The video discusses adjustments and gray areas in volumetric analysis, particularly for a specific type of titration involving potassium permanganate.
• 💡 The year's titration is not a conventional acid-based titration but a redox titration between potassium permanganate and iron(II) sulfate.
• 🔴 The end point of the titration is identified by a color change from purple to colorless and then to light pink, indicating a change in the oxidation state of the reactants.
• 🧪 Potassium permanganate (KMnO4) acts as a self-indicator due to its strong oxidizing nature, eliminating the need for an external indicator.
• 📝 The procedure for the titration involves pipetting a known volume of the base into a conical flask, acidifying with sulfuric acid, and then titrating.
• 🛡️ Acidification is crucial to prevent the oxidation of iron(II) ions to iron(III) ions before the titration, ensuring that a minimal amount of KMnO4 is used.
• ⚖️ The average volume of KMnO4 used is calculated to determine the concentration of the iron(II) sulfate solution, which is not provided directly.
• 🧮 The concentration of potassium permanganate is calculated based on the given mass and volume of the solution, resulting in a concentration of 0.01 mole per decimeter cube (M/DM³).
• 📉 The number of moles of iron(II) ions in the volume pipetted is calculated using the formula N1/V1 = N2/V2, resulting in 0.009 moles in 25 cm³ of the solution.
• 🎓 The lecture concludes with a reminder that the questions in the practical exam are highly predictable, and students are encouraged to subscribe and share the content for better preparation.

Q & A

What is the focus of the video lecture?

The video lecture focuses on volumetric analysis, also known as quantitative analysis, specifically for final revision. It discusses adjustments, gray areas, and potential changes in the exam.

What type of titration is mentioned as not being conventional this year?

The conventional acid-based titration is not being used this year. Instead, a redox titration between potassium permanganate and iron(II) sulfate is discussed.

What color change indicates the end point in the redox titration described?

The end point in the redox titration is indicated by a color change from colorless to a light pink color.

Why is potassium permanganate (KMnO4) considered a self-indicator in this context?

Potassium permanganate is considered a self-indicator because it is a strong oxidizing agent and its color changes (from purple to colorless and then to light pink) signal the end point of the titration without needing an external indicator.

What is the purpose of acidifying the potassium permanganate solution?

Acidifying the potassium permanganate solution helps to preserve the Fe2+ ions from being prematurely oxidized to Fe3+ by oxygen in the air before the titration begins, ensuring that they are available to react during the titration.

What is the economic reason behind acidifying the potassium permanganate solution?

The economic reason for acidifying the solution is to use a minimal amount of the expensive potassium permanganate (KMnO4) during the titration process.

How is the concentration of potassium permanganate (KMnO4) determined if given in grams per decimeter cube (dm³)?

The concentration of KMnO4 in moles per decimeter cube (dm³) is determined by dividing the mass of KMnO4 in grams by its molar mass and then by the volume in dm³.

What is the role of sulfuric acid (H2SO4) in the titration process?

Sulfuric acid is used to acidify the iron(II) sulfate solution, which prevents the oxidation of Fe2+ to Fe3+ and ensures that Fe2+ ions are available to react with the potassium permanganate during the titration.

What is the formula used to calculate the concentration of B (iron(II) sulfate) in moles per decimeter cube (dm³)?

The formula used to calculate the concentration of B is CB = (CA * VA * NB) / (VB * NA), where CA is the concentration of the acid, VA is the volume of acid used, NB is the number of moles of the base, VB is the volume of the base, and NA is the number of moles of the acid.

How is the average volume of potassium permanganate (KMnO4) used in the titration determined?

The average volume of KMnO4 used is determined by taking the total volume used in multiple titrations and dividing by the number of titrations performed.

What is the significance of constructing a titration table in the analysis?

Constructing a titration table helps to systematically record and analyze the volumes of titrant used, the corresponding color changes, and to calculate the average volume used. It aids in determining the concentration of the unknown solution and ensures accuracy in the results.