Hydrogen for Hire
Every use is a property in disguise
What this lesson covers
Why it matters
One gas lifts weather balloons to the edge of the sky, welds metal at 2500°C, feeds rockets, and turns liquid groundnut oil into solid vanaspati ghee. Hydrogen never gets a job it does not have the property for.
Predict first
Bubble hydrogen through soap solution. The bubbles tear free and race upward into the air. What does this prove?
Hydrogen is the lightest gas known — 14.4 times less dense than air — so hydrogen-filled soap bubbles float upward. That single property once made it the obvious filling for balloons.
- Hydrogen is far lighter than air — about 14.4 times less dense — correct
- The bubbles are hot, and hot things rise
- Hydrogen repels soap and pushes the bubbles away
What you do
Hire the right property for each job: match what hydrogen IS to what hydrogen DOES.
Check yourself
Hydrogen is collected over water in the lab because…
Colourless, odourless and nearly insoluble in water, hydrogen bubbles up through the water and fills the inverted jar without dissolving on the way.
Hydrogen lifts better than helium, yet modern airships and passenger balloons refuse to use it. Why?
A large volume of hydrogen–air mixture explodes dangerously — one spark is enough. So slightly heavier but unburnable helium carries passengers, while hydrogen still lifts unmanned weather balloons.
What makes the oxy-hydrogen flame so prized?
Burning hydrogen in oxygen gives only water and enormous heat. The 2500°C flame cuts and welds metals — and even fuses alumina into synthetic rubies and sapphires.
- it is very slightly soluble — a litre of water dissolves only about 20 mL of it — correct
- it reacts with water to make even more hydrogen
- it is denser than air, so it sinks neatly into the jar
- It forms an explosive (detonating) mixture with the oxygen in air — correct
- It has become too rare and expensive
- Its strong smell makes it unusable
- It reaches about 2500°C — hot enough to cut and weld metals and melt platinum and quartz — correct
- It burns cool, so it cannot harm the welder
- It deposits smoky carbon that marks the metal