钠与水的反应

观察碱金属与水的剧烈反应

Classroom Demonstrations Advanced (University) 25 分钟 ~$12.00

目标

通过钠与水的反应演示碱金属的活泼性，观察氢气释放和氢氧化物的生成。

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

所需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)

设备

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

步骤

1

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

3 分钟
2

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

2 分钟 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 分钟 Cut on dry surface only
4

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

1 分钟 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 分钟 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 分钟 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 分钟

预期结果

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.

清理

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

详情

类别
Classroom Demonstrations
难度
Advanced (University)
时长
25 分钟
预估费用
$12.00
步骤数
7
材料
4

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Frequently Asked Questions

What is the objective of 钠与水的反应?
通过钠与水的反应演示碱金属的活泼性，观察氢气释放和氢氧化物的生成。
How difficult is 钠与水的反应?
This experiment is rated as Advanced (University). It takes approximately 25 minutes to complete.
What safety precautions are needed for 钠与水的反应?
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 钠与水的反应?
The main materials required are: Sodium metal, Phenolphthalein indicator, Distilled water, Mineral oil.
What results should I expect from 钠与水的反应?
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.