Introduction
Barium chloride is an inorganic compound with the chemical formula BaCl2. It is a white crystalline solid that is soluble in water. When heated, barium chloride undergoes decomposition to produce a vivid green flame. So when people ask “What color does barium chloride burn?”, the answer is green.
Barium Chloride Properties
Barium chloride has several key properties:
- Chemical formula: BaCl2
- Molecular weight: 208.233 g/mol
- Appearance: White crystalline solid
- Density: 3.856 g/cm3
- Melting point: 963°C
- Boiling point: 1560°C
- Solubility: Soluble in water
As an ionic compound, barium chloride dissociates completely in water to release barium cations (Ba2+) and chloride anions (Cl-). The barium ions provide the green color when the compound burns.
Barium Chloride Flame Test
Flame tests are used to identify elements based on the color they emit when heated. When barium chloride is heated in a flame test, it imparts a vivid green color to the flame. This occurs because the barium ions are excited and emit photons in the green region of the visible spectrum.
The flame test procedure for barium chloride is straightforward:
- Obtain a clean platinum wire loop
- Dip the loop into solid barium chloride so a small amount adheres
- Place the loop into a Bunsen burner flame
- Observe the green color emitted
The green color is characteristic of barium and allows easy identification of the element. The chloride ions do not contribute to the flame color.
Barium Chloride Decomposition
When heated strongly, barium chloride decomposes according to the chemical equation:
BaCl2 (s) → BaO (s) + Cl2 (g)
Here, the solid barium chloride breaks down to produce solid barium oxide and chlorine gas. The decomposition begins around 850°C and happens readily at higher temperatures.
As the decomposition occurs, the barium ions are released and impart the green color to the flame. The chloride ions split off as chlorine gas. So the vivid green flame is a result of the excited barium ions produced during thermal decomposition.
Why Does Barium Burn Green?
The green color comes from photons emitted by the barium ions at specific wavelengths in the visible spectrum. When heated, electrons in the barium ions gain energy and jump to higher orbital levels. As they relax back down, energy is released in the form of light.
The specific transitions of electrons in barium generate photons at wavelengths of 493.4 nm and 553.5 nm, which correspond to green light. The human eye perceives this combination of wavelengths as an intense green color.
So in summary, barium burns green because:
- Barium chloride decomposes when heated to release barium ions
- Electron transitions in the barium ions emit photons in the green wavelengths
- The human eye sees this combination of wavelengths as green
No other ions contribute to the green color – it is exclusively caused by the excited barium ions.
Real-World Applications
The vibrant green flame test for barium has several practical uses:
Fireworks
Barium compounds are commonly used in fireworks to produce green colors. Barium chloride, nitrate, and chlorate are typical barium sources used in pyrotechnics. When ignited, the barium generates the characteristic green hue.
Standard for Green Color
The 523.5 nm emission line of barium ions is used as a reference standard for green colors. This wavelength defines the visual sensation of pure green. Other shades of green are mixtures of wavelengths.
Identifying Barium Compounds
The flame test is used to detect the presence of barium in an unknown sample. If the sample burns green, barium is positively identified qualitatively. The intensity of the green can also be used to quantify the barium concentration.
Green Firework Composition
Here is an example green firework composition using barium chloride:
| Chemical | Amount |
|---|---|
| Barium chloride | 20 g |
| Sodium nitrate | 80 g |
| Sulfur | 8 g |
| Polyvinyl chloride binder | 20 g |
The barium chloride provides the green color, while the sodium nitrate is the oxidizer and sulfur fuels the reaction. When ignited, this composition will burn with a brilliant green flame.
Proper safety precautions should always be taken when working with pyrotechnic mixtures.
Conclusion
In summary, barium chloride burns with a vivid green flame when heated. This occurs because the decomposed barium ions emit photons in the green wavelengths of the visible spectrum. The green color has many practical uses, from fireworks to identifying barium compounds. So next time you see a green sparkler or firework, you’ll know it’s due to barium!
