A barking test tube

What happens when hydrogen burns

Can you make a test tube bark?

Safe­ty pre­cau­tions

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.

Step-by-step in­struc­tions

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.

Process de­scrip­tion

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

Try it