ナトリウムと水の反応

アルカリ金属と水との激しい反応を観察する

Classroom Demonstrations Advanced (University) 25 分 ~$12.00

目的

ナトリウムを水と反応させてアルカリ金属の反応性を実証し、水素の発生と水酸化物の生成を観察する。

背景

Sodium metal reacts vigorously with water in a classic demonstration of alkali metal reactivity: 2Na + 2H₂O → 2NaOH + H₂. The sodium skates across the water surface as hydrogen gas is evolved, often melting into a ball from the heat of reaction. Adding phenolphthalein indicator to the water reveals the spreading pink color of NaOH as it forms. This reaction illustrates metallic bonding (soft metal), oxidation states, and the trend of increasing reactivity down Group 1.

安全上の警告

  • Sodium is highly reactive — NEVER handle with bare hands
  • Keep sodium away from water until ready for demonstration
  • Cut sodium on a dry tile; keep pieces small (pea-sized maximum)
  • Use safety shield between reaction and audience
  • Hydrogen gas is flammable — larger pieces may ignite the hydrogen
  • NaOH solution formed is corrosive
  • Never use pieces larger than a small pea for this demonstration

必要なPPE

goggles gloves lab_coat face_shield

材料

  • Sodium metal (1 small piece)
    Pea-sized, stored under mineral oil
  • Phenolphthalein indicator (5 mL)
    Added to water
  • Distilled water (500 mL)
  • Mineral oil (For storage)

器具

Large glass trough or crystallizing dish Safety shield Forceps Scalpel or knife (for cutting sodium) Filter paper Tile for cutting

手順

1

Fill the trough with about 300 mL of water. Add a few drops of phenolphthalein indicator. Set up the safety shield.

3 分
2

Using forceps, remove a small piece of sodium from the mineral oil. Blot excess oil with filter paper on a dry tile.

2 分 Keep all water away from cutting area
3

Cut a very small piece (no larger than a pea). Return the remainder to the mineral oil.

2 分 Cut on dry surface only
4

Drop the sodium piece into the water from behind the safety shield. Step back immediately.

1 分 STEP BACK after dropping
5

Observe: the sodium floats, melts into a ball, darts across the surface, fizzes (H₂ evolution), and the water turns pink (NaOH + phenolphthalein).

5 分 Do not lean over the trough
6

After the reaction is complete, test the pH of the solution with pH paper (should be >12).

3 分 Solution is now corrosive NaOH
7

Discuss: Group 1 reactivity trend (Li < Na < K < Rb < Cs), the redox nature of the reaction, and why sodium floats (density 0.97 g/mL < 1.0 g/mL).

7 分

予想される結果

The sodium piece fizzes vigorously on the water surface, darting around as hydrogen is released. It melts into a shiny ball. The phenolphthalein turns the water bright pink in a spreading pattern. With very small pieces, no flame occurs; slightly larger pieces may produce a yellow sodium flame.

後片付け

Neutralize the NaOH solution with dilute HCl before disposing down the drain. Ensure no unreacted sodium remains. Clean the trough thoroughly.

詳細

カテゴリ
Classroom Demonstrations
難易度
Advanced (University)
所要時間
25 分
推定費用
$12.00
ステップ数
7
材料
4

その他の実験

テルミット反応 30 min ドライアイス中でのマグネシウムの燃焼 25 min ヨウ素時計反応 45 min ルミノールによる化学発光 30 min 密度カラム虹 30 min 振動するブリッグス-ラウシャー反応 40 min 消えるビーカー（屈折率マッチング） 15 min 瞬間凍結：過冷却水 120 min 象の歯磨き粉 20 min 非ニュートン流体：ウブレック 20 min

Frequently Asked Questions

What is the objective of ナトリウムと水の反応?
ナトリウムを水と反応させてアルカリ金属の反応性を実証し、水素の発生と水酸化物の生成を観察する。
How difficult is ナトリウムと水の反応?
This experiment is rated as Advanced (University). It takes approximately 25 minutes to complete.
What safety precautions are needed for ナトリウムと水の反応?
Key safety precautions include: Sodium is highly reactive — NEVER handle with bare hands; Keep sodium away from water until ready for demonstration; Cut sodium on a dry tile; keep pieces small (pea-sized maximum).
What materials are needed for ナトリウムと水の反応?
The main materials required are: Sodium metal, Phenolphthalein indicator, Distilled water, Mineral oil.
What results should I expect from ナトリウムと水の反応?
The sodium piece fizzes vigorously on the water surface, darting around as hydrogen is released. It melts into a shiny ball. The phenolphthalein turns the water bright pink in a spreading pattern. With very small pieces, no flame occurs; slightly larger pieces may produce a yellow sodium flame.