# What's happening in this water electrolysis? **URL:** \ **Category:** Factual Questions\ **Tags:** science-math\ **Created:** [October 24, 2024, 10:34pm UTC](https://boards.straightdope.com/t/whats-happening-in-this-water-electrolysis/1009176 "2024-10-24T22:34:07Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [October 24, 2024, 10:34pm UTC](https://boards.straightdope.com/t/whats-happening-in-this-water-electrolysis/1009176/1 "2024-10-24T22:34:07Z")
My science teacher friend says the blackened test tube is getting the least gas, which would mean it’s the oxygen side. This invalidates my guess and theory, so I’m asking here. Why is the tube getting black at the top? Is pulling in electrons breaking graphite covalent bonds? I thought supplying electrons would do that job, but I was guessing. > **[Electrolysis.jpg](https://drive.google.com/file/d/1gXd_OCeCsltTCh5kFS2nxe8OdmhU0uPY/view?usp=sharing)** > > Google Drive file. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [October 25, 2024, 3:27pm UTC](https://boards.straightdope.com/t/whats-happening-in-this-water-electrolysis/1009176/2 "2024-10-25T15:27:52Z")
> [@Cardinal](#): > > Is pulling in electrons breaking graphite covalent bonds? There should be no graphite in there. The tubes should have been full of just distilled water when the electrolysis started. ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [October 25, 2024, 9:19pm UTC](https://boards.straightdope.com/t/whats-happening-in-this-water-electrolysis/1009176/3 "2024-10-25T21:19:33Z")
> [@Cardinal](#): > > Why is the tube getting black at the top? Is pulling in electrons breaking graphite covalent bonds? Water electrolysis anodes are prone to corrosion. You’re seeing surface oxidation and freeing of polyaromatic “soot”. ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [October 26, 2024, 1:31pm UTC](https://boards.straightdope.com/t/whats-happening-in-this-water-electrolysis/1009176/4 "2024-10-26T13:31:10Z")
Maybe it’s me, but I see no wires providing the power for the electrolysis? And pencils as electrodes? ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [October 26, 2024, 3:57pm UTC](https://boards.straightdope.com/t/whats-happening-in-this-water-electrolysis/1009176/5 "2024-10-26T15:57:24Z")
Understandable. It’s a single photo of a weird display of transparent tubes and transparent liquid using seemingly intentionally obscured wires carrying unseeable electrical currents to capture invisible gases while throwing us all off using household items as electrodes for some reason. The least surprising thing about this exercise is that pencils blacken things. ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [October 26, 2024, 7:13pm UTC](https://boards.straightdope.com/t/whats-happening-in-this-water-electrolysis/1009176/6 "2024-10-26T19:13:08Z")
> [@GaryM](#): > > And pencils as electrodes? ETA wrong link. But yes, the graphite makes for a reasonable home electrode. Here’s the right link: > **[Biosensing based on pencil graphite electrodes](https://www.sciencedirect.com/science/article/abs/pii/S0039914018307963)** > > Pencil leads have been increasingly used as electrode material in electrochemical applications. Commonly denominated as pencil graphite electrodes (PG…