Réaction du Sodium avec l'Eau

Observation de la réaction vigoureuse d'un métal alcalin avec l'eau

Classroom Demonstrations Advanced (University) 25 min ~$12,00

Objectif

Démontrer la réactivité des métaux alcalins en faisant réagir du sodium avec de l'eau, en observant le dégagement d'hydrogène et la formation d'hydroxyde.

Contexte

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.

Avertissements de sécurité

  • 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

EPI requis

goggles gloves lab_coat face_shield

Matériaux

  • 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)

Équipement

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

Procédure

1

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

3 min
2

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

2 min 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 min Cut on dry surface only
4

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

1 min 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 min 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 min 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 min

Résultats attendus

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.

Nettoyage

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

Détails

Catégorie
Classroom Demonstrations
Difficulté
Advanced (University)
Durée
25 min
Coût estimé
$12,00
Étapes
7
Matériaux
4

Plus d'expériences

Bécher Invisible (Correspondance d'Indice de Réfraction) 15 min Chimioluminescence avec le Luminol 30 min Colonne Arc-en-ciel de Densités 30 min Congélation Instantanée : Eau Surfusionnée 120 min Dentifrice d'Éléphant 20 min Fluide Non Newtonien : Oobleck 20 min Magnésium Brûlant dans la Glace Carbonique 25 min Réaction de l'Horloge à Iode 45 min Réaction Oscillante de Briggs-Rauscher 40 min Réaction Thermite 30 min

Frequently Asked Questions

What is the objective of Réaction du Sodium avec l'Eau?
Démontrer la réactivité des métaux alcalins en faisant réagir du sodium avec de l'eau, en observant le dégagement d'hydrogène et la formation d'hydroxyde.
How difficult is Réaction du Sodium avec l'Eau?
This experiment is rated as Advanced (University). It takes approximately 25 minutes to complete.
What safety precautions are needed for Réaction du Sodium avec l'Eau?
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 Réaction du Sodium avec l'Eau?
The main materials required are: Sodium metal, Phenolphthalein indicator, Distilled water, Mineral oil.
What results should I expect from Réaction du Sodium avec l'Eau?
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.