The Gas Ratio Tells It All! The Thrill of Water Electrolysis with an H-Tube

I’m Ken Kuwako, the Science Trainer. Every day is an experiment.

Electrolysis of water is one of the most iconic chemistry experiments, and using an H-shaped tube makes it even more spectacular. Today, I’d like to share why this classic demonstration is still one of my favorites—and how it beautifully brings a simple chemical formula to life.

Few moments in science are as exciting as hearing a tiny “pop!” during an experiment. This time, together with Mr. T, we carried out the timeless experiment of electrolyzing water using an H-tube. Even after seeing it countless times, it’s still impossible not to be amazed.

Why We Chose an H-Tube

This H-tube is designed with a water reservoir that allows gases to be collected efficiently. Since it’s made of glass, it’s relatively expensive and can break if handled carelessly. That’s why, in regular classroom lessons, I usually use smaller electrolysis kits instead.

【動画で解説】水の電気分解実験、準備から片付けまで徹底網羅！

But the H-tube offers several advantages that smaller devices simply can’t match. You can collect the gases directly through the stopcocks, and more importantly, the larger size makes the entire experiment far more dramatic to watch. When you’re demonstrating chemistry in front of a classroom, that visual impact makes all the difference.

The Beautiful 1:2 Ratio

As electricity flows through the water, oxygen begins to form at the anode while hydrogen is produced at the cathode. Watching the water level slowly move as more gas is generated is surprisingly satisfying.

After a while, something remarkable becomes clear: the volume of gas collected settles into a perfect 1:2 ratio.

This isn’t a coincidence. It’s direct evidence of water’s chemical formula, H₂O. Every water molecule contains two hydrogen atoms and one oxygen atom, and that invisible molecular structure reveals itself as a visible ratio of gases.

That’s what makes this experiment so fascinating. The hidden world of atoms suddenly becomes something you can actually see with your own eyes.

What Happens When You Bring in a Flame?

Next, we tested each gas with a flame. Here’s what happened.

Hydrogen burns with a distinctive “pop,” while oxygen doesn’t burn itself—it supports combustion, making other materials burn more vigorously.

Oxygen

Hydrogen

Reading about these properties in a textbook is one thing, but seeing them happen right before your eyes is something completely different. No matter how many times I perform this experiment, it still brings that same sense of wonder.

Using a large H-tube makes the experience much more powerful than using a compact classroom apparatus. An everyday substance as ordinary as water transforms into two completely different gases with nothing more than electricity. Even more amazing, the amounts of those gases perfectly reflect the molecular structure of water itself.

It’s a wonderful reminder that chemistry isn’t just a collection of formulas—it’s a way of revealing the invisible rules that shape our world.

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