A barking test tube
What happens when hydrogen burns
Can you make a test tube bark?
Wear protective gloves, eyewear, and a mask. Perform this experiment in a well-ventilated area. Observe safety precautions when working with fire.
Reagents and equipment
- 10 g zinc;
- 30 mL 20% sulfuric acid solution;
- a conical flask;
- a rubber stopper with one tube;
- a test tube;
- a candle;
- a lighter or matches.
Pour 10 g zinc into the conical flask and add 30 mL of 20% sulfuric acid solution. Observe the tumultuous release of colorless gas. Close the flask using the stopper with one tube. Hold the test tube over the tube tip to collect the forming gas. Light the candle. Keeping the test tube upside down, bring its neck to the burning candle. You will hear a sharp sound reminiscent of a dog’s bark.
Sulfuric acid and zinc react, producing colorless hydrogen gas:
Zn + H₂SO₄ = ZnSO₄ + H₂↑
As hydrogen gas is lighter than air, it can be collected by holding the test tube upside down over the source. Burning pure hydrogen results in a small pop, and hydrogen mixed with oxygen results in a characteristic barking sound. In the laboratory, this method can be used to test the purity of obtained hydrogen.
2H₂ + O₂ = 2H₂O