Sulfur burns in oxygen: properties of sulfur dioxide; test with acidified potassium dichromate paper

Summary

In this chemistry video, sulfur burns in oxygen to form sulfur dioxide, which is observed with a blue flame. The experiment tests sulfur dioxide's acidic and reducing properties using acidified potassium dichromate and distilled water with a universal indicator. The video explains the chemical equations behind these properties, showing sulfur dioxide's ability to form sulfurous acid and its reduction potential when reacting with oxidizing agents like potassium dichromate.

Takeaways

• 🔥 Sulfur burns in oxygen to produce sulfur dioxide, which is a colorless gas.
• 🔵 Burning sulfur in oxygen produces a bright blue flame, which can be difficult to see in air.
• 🧪 Sulfur dioxide can be tested by its reducing properties using acidified potassium dichromate; it changes color from orange to green.
• 🌡️ Sulfur dioxide is an acidic gas, as demonstrated by its reaction with water and changing the pH of the solution to acidic (pH below 4).
• 🌊 Sulfur dioxide reacts with water to form sulfurous acid, which is a weak acid.
• ⚛️ Sulfurous acid, formed from sulfur dioxide and water, demonstrates reducing properties by giving up oxygen.
• 🔋 Sulfur dioxide has an oxidation state of +4 and can be oxidized to sulfate, which has an oxidation state of +6.
• 🌡️ Sulfite ions are oxidized to sulfate ions, losing two electrons in the process.
• ⚖️ The reaction between sulfur dioxide and dichromate ions demonstrates redox chemistry, where dichromate is reduced to chromium (III) and sulfur dioxide is oxidized.
• 📊 The balanced half-equations for the reduction of dichromate and oxidation of sulfite are provided, showing electron transfer processes.

Q & A

What is the purpose of the experiment in the video?

The purpose of the experiment is to burn sulfur in oxygen and observe the properties of the resulting product, sulfur dioxide.

What is the visual indication that sulfur has started burning?

Although the flame is difficult to see in air, it becomes visible as a bright blue flame when sulfur burns in oxygen.

What chemical equation describes the burning of sulfur in oxygen?

The balanced chemical equation is: S (solid) + O₂ (gas) → SO₂ (gas), where sulfur reacts with oxygen to produce sulfur dioxide.

How is the reducing property of sulfur dioxide demonstrated in the experiment?

The reducing property of sulfur dioxide is demonstrated using acidified potassium dichromate. When exposed to sulfur dioxide, the orange potassium dichromate turns green.

What is the test for sulfur dioxide's presence using acidified potassium dichromate?

The test for sulfur dioxide involves dipping filter paper in acidified potassium dichromate. When exposed to sulfur dioxide, the paper changes color from orange to green.

How is the acidic nature of sulfur dioxide shown in the experiment?

The acidic nature of sulfur dioxide is shown by dissolving it in water containing a universal indicator. The water turns from green (neutral) to a color indicating an acidic pH, around 4 or lower.

Why is sulfur dioxide considered an acidic gas?

Sulfur dioxide is considered an acidic gas because it is a non-metallic oxide that reacts with water to form sulfurous acid (H₂SO₃), a weak acid.

What is the balanced half-reaction for the oxidation of sulfite (SO₃²⁻) to sulfate (SO₄²⁻)?

The balanced half-reaction is: SO₃²⁻ + H₂O → SO₄²⁻ + 2H⁺ + 2e⁻. Sulfite is oxidized to sulfate by losing two electrons.

What is the balanced half-reaction for the reduction of dichromate (Cr₂O₇²⁻) to chromium (Cr³⁺)?

The balanced half-reaction is: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O. Each chromium atom is reduced from an oxidation state of +6 to +3, gaining a total of 6 electrons.

Why does potassium dichromate change color during the reaction with sulfur dioxide?

Potassium dichromate changes color from orange to green because the dichromate ion (Cr₂O₇²⁻) is reduced to chromium (Cr³⁺) by the sulfur dioxide, indicating a reduction process.