Sodium in Water

A pea-sized piece of sodium metal is placed on water, where it reacts exothermically to form sodium hydroxide and hydrogen gas. Heat from the reaction can ignite the hydrogen, and a pH indicator shows the solution becoming alkaline.

Note: this uses a tiny piece of sodium that shouldn't explode. See here for the explosive version.

1. Place a beaker in a secondary tray and fill it about halfway with water.
2. Add a few drops of a pH indicator such as phenolphthalein to the water.
3. Using dry tongs, cut and remove a pea-sized piece of sodium from oil storage and quickly blot surface oil with a dry tissue.
4. Stand back and gently place the sodium piece onto the water surface.
5. Observe fizzing, the metal skittering on the surface, hydrogen evolution, possible ignition, and the indicator trail turning pink as sodium hydroxide forms.

Reaction of Sodium and Water - North Carolina School of Science and Mathematics:

📄 Sodium in Water Chemistry Demonstration - Science Notes: https://sciencenotes.org/sodium-in-water-chemistry-demonstration/

• Use different indicators (phenolphthalein, universal indicator) to visualize the pH increase.
• Demonstrate group trends qualitatively by discussing lithium (milder) and potassium (more vigorous) behavior rather than performing them, or show vetted video clips for comparison.

• Teacher demonstration only; do not scale up the sample size beyond pea-sized.
• Wear splash goggles, face shield, lab coat, and appropriate gloves; keep students behind a safety shield and at a safe distance.
• Store sodium under mineral oil or kerosene; handle with dry tools and dry hands away from water sources.
• Use only a borosilicate beaker placed in a larger tray for containment; keep flammables away.
• Expect hydrogen gas; avoid open flames and ignition sources.
• Keep a Class D option such as dry sand available; do not use water or CO₂ extinguishers on alkali metal fires.
• After the reaction, treat the solution as sodium hydroxide; optionally neutralize with dilute acid (e.g., vinegar) before disposal per local rules.

• Why does sodium float on water? (Its density is about 0.97 g/cm³, lower than water.)
• What products form in the reaction, and how does the indicator show this? (Sodium hydroxide and hydrogen; the base raises pH so phenolphthalein turns pink.)
• Why can flames appear even without an external spark? (The exothermic reaction can heat and ignite the hydrogen in air.)
• Why is sodium metal far more reactive than sodium chloride in water? (Na metal readily loses an electron; in NaCl the sodium already exists as Na⁺ and simply dissolves.)
• How does reactivity change down Group 1, and why? (It increases from Li to Cs due to lower ionization energy and weaker attraction to the outer electron.)