干冰中的镁燃烧

镁在固态二氧化碳中持续燃烧，将CO₂还原为碳

Classroom Demonstrations Advanced (University) 25 分钟 ~$15.00

目标

演示镁能够还原二氧化碳，挑战CO₂总能灭火的错误认知。

背景

Magnesium burns so intensely (over 3000°C) that it can reduce carbon dioxide to elemental carbon. When a burning magnesium ribbon is placed in a cavity carved into dry ice (solid CO₂), it continues to burn brilliantly white, producing magnesium oxide (white powder) and elemental carbon (black specks). This reaction (2Mg + CO₂ → 2MgO + C) dramatically shows that CO₂ is not always an effective fire extinguisher and that thermodynamic favorability depends on the specific reactants involved.

安全警告

  • Burning magnesium is extremely bright — never look directly at it without shade protection
  • Dry ice causes frostbite on contact — never handle with bare hands
  • Perform behind a safety shield
  • Keep a fire-resistant mat underneath
  • Do not attempt to extinguish burning Mg with water — explosion risk
  • Ensure ventilation — CO₂ accumulation in enclosed spaces is dangerous

所需PPE

goggles gloves lab_coat face_shield

材料

  • Magnesium ribbon (30 cm)
    Clean, bright surface
  • Dry ice block (1 kg)
    Solid CO₂ (−78.5°C)
  • Tongs (long-handled) (1)
    For handling dry ice

设备

Safety shield Fire-resistant mat Chisel or screwdriver (for carving cavity in dry ice) Lighter or matches Welding goggles or #14 shade glass

步骤

1

Using tongs, carve a small cavity (about 3 cm deep) in the dry ice block. Place the dry ice on a fire-resistant mat.

3 分钟 Wear insulated gloves for dry ice
2

Set up the safety shield between the demonstration and the audience. Distribute welding goggles or instruct everyone to look away when ignited.

2 分钟
3

Light one end of the magnesium ribbon. Once burning, quickly place it in the dry ice cavity using tongs.

2 分钟 Do not look directly at the flame
4

Place another piece of dry ice on top to create a CO₂ atmosphere around the burning magnesium.

2 分钟
5

Observe: the magnesium continues to burn with an intense white flame inside the CO₂ environment. It does NOT go out.

3 分钟 Maintain safe distance
6

After the reaction, examine the residue: white MgO powder and black carbon specks. Discuss the reaction: 2Mg + CO₂ → 2MgO + C.

8 分钟 Wait for residue to cool completely
7

Discuss implications for fire safety: why Mg fires cannot be extinguished with CO₂, water, or standard fire extinguishers.

5 分钟

预期结果

The magnesium continues to burn brilliantly inside the dry ice. After the reaction, white MgO and black carbon specks are visible in the dry ice cavity. This proves CO₂ has been reduced to elemental carbon.

清理

Allow all residues to cool and dry ice to sublimate. Sweep up MgO and carbon residue. No chemical waste disposal needed.

详情

类别
Classroom Demonstrations
难度
Advanced (University)
时长
25 分钟
预估费用
$15.00
步骤数
7
材料
3

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Frequently Asked Questions

What is the objective of 干冰中的镁燃烧?
演示镁能够还原二氧化碳，挑战CO₂总能灭火的错误认知。
How difficult is 干冰中的镁燃烧?
This experiment is rated as Advanced (University). It takes approximately 25 minutes to complete.
What safety precautions are needed for 干冰中的镁燃烧?
Key safety precautions include: Burning magnesium is extremely bright — never look directly at it without shade protection; Dry ice causes frostbite on contact — never handle with bare hands; Perform behind a safety shield.
What materials are needed for 干冰中的镁燃烧?
The main materials required are: Magnesium ribbon, Dry ice block, Tongs (long-handled).
What results should I expect from 干冰中的镁燃烧?
The magnesium continues to burn brilliantly inside the dry ice. After the reaction, white MgO and black carbon specks are visible in the dry ice cavity. This proves CO₂ has been reduced to elemental carbon.