Lab Experiment #5: Volumetric Analysis by RedOx Titration.

Summary

This video demonstrates how to determine the purity of a solid using volumetric analysis through a redox titration. The process involves preparing a solution from an impure solid, titrating it with potassium permanganate, and calculating the concentration of the solution. By using stoichiometry and the redox reaction between potassium permanganate and iron(II) ions, the video guides viewers through the steps of determining the exact concentration and purity of the solid. The titration procedure includes rough and accurate titrations, with the final goal of calculating the percent purity of the iron sulfate heptahydrate sample.

Takeaways

• 😀 The purpose of the video is to demonstrate how to determine the purity of a solid using volumetric analysis through redox titration.
• 😀 The solid being tested is impure, meaning the concentration of the solution cannot be calculated directly from the mass of 2.5 grams of the solid.
• 😀 The titration reaction is a redox reaction between potassium permanganate (KMnO₄) and iron(II) sulfate (FeSO₄) in an acidic medium.
• 😀 The balanced redox equation for the reaction is: MnO₄⁻ + 5 Fe²⁺ + 8 H⁺ → Mn²⁺ + 5 Fe³⁺ + 4 H₂O.
• 😀 Stoichiometry between potassium permanganate and iron sulfate is 1:5, which helps in calculating the relationship between their molarities.
• 😀 The molarity of KMnO₄ is known (0.02 M), and this can be used to calculate the molarity of the iron sulfate solution by performing a titration.
• 😀 Once the molarity of the iron sulfate solution is determined, it allows for the calculation of the pure mass of iron sulfate heptahydrate in the sample.
• 😀 The purity of the solid can be determined by dividing the mass of pure iron sulfate by the initial 2.5 grams, and multiplying by 100 to get the percent purity.
• 😀 To begin the experiment, the burette should be filled with potassium permanganate, and 10 mL of the iron sulfate solution should be prepared for titration.
• 😀 The titration involves adding potassium permanganate to the iron sulfate solution in incremental amounts, starting with rough titration and then proceeding to more accurate titrations after observing color changes.

Q & A

What is the purpose of the redox titration in this experiment?

The purpose of the redox titration in this experiment is to determine the purity of a solid (iron sulfate heptahydrate) by calculating the concentration of the iron sulfate solution through volumetric analysis.

Why is the concentration of the iron sulfate solution not initially calculable from the mass of the solid used?

The concentration cannot be calculated directly from the mass of the solid because the iron sulfate used is impure. The actual mass of pure iron sulfate is less than the 2.5 grams weighed, affecting the concentration.

How is the concentration of the iron sulfate solution determined?

The concentration is determined through titration, where potassium permanganate (the titrant) reacts with the iron(II) sulfate solution. The relationship between the moles of potassium permanganate and iron sulfate, derived from the balanced redox reaction, allows the calculation of the solution's concentration.

What is the significance of the balanced redox reaction between potassium permanganate and iron sulfate?

The balanced redox reaction provides the stoichiometric relationship between potassium permanganate (MnO₄⁻) and iron(II) sulfate (Fe²⁺). This relationship is used to calculate the moles of iron sulfate in the solution from the volume of potassium permanganate used during the titration.

What does the molar ratio in the redox reaction (1:5) represent?

The molar ratio of 1:5 means that for every 1 mole of potassium permanganate (MnO₄⁻) used, 5 moles of iron(II) ions (Fe²⁺) are involved in the reaction.

How is the percent purity of the iron sulfate determined in this experiment?

The percent purity of the iron sulfate is determined by calculating the mass of pure iron sulfate from the titration results and then dividing it by the initial mass of the impure sample (2.5 grams), multiplying by 100%.

Why is acid added to the solution during the titration?

Acid is added to the solution to speed up the redox reaction between potassium permanganate and iron(II) sulfate. Without the acid, the reaction would be very slow.

What is the role of the burette in the titration?

The burette holds the potassium permanganate solution (the titrant) and is used to add it to the iron sulfate solution in a controlled manner to determine the volume needed for the reaction to reach its endpoint.

What is the purpose of performing a rough titration before the accurate titrations?

The rough titration is performed to estimate the volume of potassium permanganate required to complete the reaction. This helps in setting a reasonable starting point for the accurate titrations.

How do you know when to stop the titration?

The titration is stopped when the color change becomes permanent, indicating that the reaction has reached its endpoint. This happens when the excess potassium permanganate has reacted with all the iron(II) ions.