Hydrogen gives a squeaky pop with a burning splint at the mouth of a tube of collected gas. Oxygen relights a glowing splint. Both require supervised flame testing.
Carbon dioxide turns limewater cloudy because calcium carbonate forms. Chlorine bleaches damp litmus paper white. Chlorine is toxic, so treat this as a written test, not an invitation to make the gas.
A gas coming off a reaction does not identify itself. Choose a test, observe its result and limit your conclusion to what that test establishes.
Worked example
Bubbles form when an unknown solid reacts with dilute acid. This alone does not identify hydrogen or carbon dioxide.
Collected gas turns limewater milky: carbon dioxide is supported by that test.
Copy these details if you'd like to report a problem. Your answers and history aren't included. Nothing is sent automatically.
Write an explanation
Why is bubbling alone insufficient evidence for hydrogen?
Compare your explanation with the points below. The text you type isn't marked, saved or sent anywhere.
Compare with the example
Check your explanation for
Explain what bubbling actually shows.
Name the hydrogen test.
State the expected observation.
Example answer
Bubbling shows a gas is being produced. Hydrogen is identified by the characteristic squeaky pop with a burning splint applied to collected gas under supervised conditions.
An answer to improve
All acids give hydrogen, so bubbles confirm it.
Improve your answer
Use the given evidence and conditions to repair the unsupported claim in your first answer.
Save your progress
Your progress stays in this browser. Turn on saving if you want to keep it when you leave the page.