Blue and violet cornflowers blossom on a Petri dish.
name: Sodium reacts with alcohol mixture producing strong bases.
Wear eye protection goggles and gloves. Be careful handling sodium. All the equipment should be dry.
Always follow general safety
recommendations. Please note that conducting chemistry
experiments you must comply with the relevant legal procedures in
2C2H5OH + 2Na → 2C2H5ONa + H2
2(СН3)2СНОН + 2Na → 2(СН3)2СНОNa + H2
- Prepare an indicator solution. Dissolve 0.5 gram of bromothymol blue and 1.5 grams of phenolphthalein in 40 grams of isopropanol. The resulting solution has a yellow color.
- Add a few drops of ethanol to the indicator solutions.
- Pour the obtained mixture on the Petri dish.
- Cut a few small pieces of metallic sodium.
- Place the metal pieces at the distant parts of the Petri dish.
- The observed picture resembles blossoming cornflowers.
- Repeat the experiment adding more ethanol.
- The changes speed up.
- Repeat the experiment replacing isopropanol with kerosene.
- The changes slow down.
Sodium is an active alkaline metal. It reacts with alcohol mixture forming sodium ethoxide. Sodium ethoxide is a very strong base. It shifts the pH of the surrounding environment to the alkaline region. This in turn causes the color change of added indicators. Phenolphthalein turns purple and bromothymol blue turns blue. The rate of the reaction with sodium is different in the case of ethanol and isopropanol. Ethanol reacts faster than isopropanol because its hydrocarbon radical is shooter and less branched. In the case of ethanol such structure of the hydrocarbon radical causes distribution of electron density more favorable for the reaction with sodium than in the case of isopropanol. Since isopropanol and ethanol have different viscosity the diffusion flow of alkali creates “flowers”. Kerosene does not react with sodium so if isopropanol is replaced with kerosene the reaction passes only with ethanol and rate of “flower blossoming” decreases.