Dr. Stone is definitely worth watching if you're a Chemistry nerd like me. Yes, it's on the geekier, dorkier side of Netflix, but damn, this anime serves up the good stuff.
In Dr. Stone, the human race was brought back to the Stone Ages, where everyone had been petrified (literally turned into stone) and only a few survivors were left. Like most animes, this one got pretty dark too.
The survivors, led by a scientific genius, Senku, used their Physics, Biology and Chemistry knowledge to help solve their problems one step at a time. When one of their members, Ruri, fell gravely ill, the team headed out on a mission to find sulfuric acid, synthesise antibiotics and cure her. I know, a lofty-as-hell mission for people living in the Stone Ages.
Venturing into the unknown, Senku and his team discovered a lustrous, gleaming emerald lake of sulfuric acid. Just collect a vial of acid and leave, right? Easier said than done! Watch their adventure here (watch in fullscreen for subtitles):
Yes, I know what's on everyone's minds. Damn, sulfuric acid is some pretty hot stuff. But let’s not get sidetracked by Sulfurina-chan over there. Our real quest is figuring out what turned that silver spear black, right? cue enthusiastic children’s “YEAAAAA!!” sound effect.
So, when Senku (the guy with the huge spring onion head) said that the sulfuric acid lake was enveloped by toxic gases, like hydrogen sulfide and sulfur dioxide, he meant serious business. Hydrogen sulfide (H₂S), in particular, smells like rotten eggs. If you've ever hiked up to the crater of a volcano, it's a smell that you could never miss. Hydrogen sulfide is highly toxic – second only to carbon monoxide as a cause of inhalational deaths. It halts cellular respiration, causing you to lose consciousness due to a lack of oxygen travelling to the brain. And it doesn't just knock you out! Breathing in too much hydrogen sulfide can cause hallucinations, which was exactly what happened to Ginro, who was seduced by imaginary hot babe Sulfurina-chan. Literally blinded by love. The black birds, unfortunately, had no lovely friends to save them from the hot spring of sulfuric acid.
And that is why Senku and his team crafted a silver spear to "sense" the toxic hydrogen sulfide. Btw, the silver spear ain't some mystical omniscient sage that can feel or magically become aware of the gases around it. This can all be explained through Chemistry.
Silver reacts with hydrogen sulfide, sulfur or other sulfur compounds to form silver sulfide, which is the black substance we see forming on the silver spear:
Ag (s) + H₂S → Ag₂S (s) + H₂ (g)
Silver sulfide is also commonly known as tarnish, or blackened silver. You might sometimes see tarnish on old plates and cutlery at home, which could be due to contact with food or items such as hardboiled eggs, mayonnaise, mustard, and rubber bands which all contain sulfur or sulfur compounds. Same for silver jewellery or silver coins that have been left untouched for a while. In air, a silver object can tarnish owing to the reaction of silver with hydrogen sulfide. Don't worry, you should be fine – hydrogen sulfide is found in air at very low concentrations! It is usually produced as a result of some industrial processes and the decomposition of dead plants and animals.
So, if any of your friends start calling those brown or black stains on their silverware "rust," you can swoop in with your newfound knowledge and say, "Actually, my dear Watson, rust is iron oxide. What you’re seeing here is tarnish—silver sulfide, to be precise!" Just don’t come crying to me when your friends start avoiding you like the plague.
But hold up – if hydrogen sulfide is stinky as hell, why did Senku and his team need a silver spear to "sense" it? Can't they just use their noses? Well, at very high concentrations (~100ppm) of hydrogen sulfide, your olfactory senses get overwhelmed, and you will not be able to smell it anymore. Scary stuff, huh? Maybe this spectrum will help you to visualise things better:
Removing tarnish from the silver spear
Senku later tried to polish the silver spear by abrasion, rubbing off the black coating using an alkali base. Although this method works, it isn't exactly very efficient, and results in a loss of silver as well.
A more efficient way to remove tarnish is actually through a redox reaction which is 100% safe and easy to carry out at home (check your cupboards for tarnished cutlery if you want to try this out!).
You only need a few ingredients! In a bowl, simply lay down some aluminium foil, then add some baking soda, table salt and warm water. Place your tarnished silverware in the bowl and voilà! In a short while, your silverware would look as good as new.
Aluminium is more reactive than silver, so it displaces silver in silver sulfide, purifying the silver. This is a redox reaction represented by the following equation:
3 Ag₂S(s) + 2 Al(s) ---> 6 Ag(s) + Al₂S₃(s)
Here, Ag is reduced (from an oxidation state of +1 to 0) and Al is oxidised (from an oxidation state of 0 to +3). The baking soda and salt contributes ions, creating a highly conductive environment where this redox reaction can take place.
People of the likes of Amber Heard and Ellen Degeneres could probably do with some aluminium and redox chemistry, considering how much help they would need to clean up their tarnished reputation.
Inside the gas mask
Being the genius that he is, Senku created gas masks to protect his team from the toxic gases. Equipped with the gas masks, they set out on a second, very valiant trip to obtain sulfuric acid. Watch the clip below:
How did Senku create those gas masks? In the clip, he mentioned two ingredients, both of which he extracted from bamboo ash:
Activated charcoal
Potassium carbonate
Activated charcoal is the ingredient that does the magic here! It is a carbon powder that has very high surface area: volume ratio.
This is an electron microscope image of activated charcoal. Check out all the holes in this thing (oops, sorry for triggering your trypophobia).
Activated carbon is very porous, and by having such high surface area, it attracts toxic gas molecules, which adsorb onto its surface. The basic potassium carbonate also helps by neutralising the acidic gases encountered by Senku and his team:
Reaction with H₂S: H₂S + K₂CO₃ -> K₂S + H₂O + CO₂
Reaction with SO₂: SO₂ + K₂CO₃ -> CO₂ + K₂SO₃
Real-life sulfuric acid lakes
What we see in Dr. Stone actually isn't too crazy – did you know that some of these beautiful, pristine acid lakes exist in nature? Some of them are tourist destinations which you can visit, if this blog post hasn't already deterred you enough.
If you’re an adventure and hiking fan, you need to add Kawah Ijen, an active volcano in East Java to your bucket list. Check out that insaneee blue lake of acid at its crater:
Looks tempting to swim in right? Please, manage your intrusive thoughts at all costs. The pH of the lake water, containing hydrochloric and sulfuric acids is less than 0.3, meaning it can dissolve metal, much less your body. These lakes are 100% natural, and they are formed when acidic gases, such as sulfur dioxide, hydrogen sulfide and hydrogen chloride released by the active volcano dissolve in water. Let's pray that if we visit, we don't lose our footing like the boy in Dr. Stone did.
Andd.. that's not the only cool thing about Kawah Ijen. Check out the stunning blue flames of Mt. Ijen:
Is that you, Azula?? At Kawah Ijen, extremely high quantities of sulfuric gases emerge at high pressures and temperatures (sometimes in excess of 600°C) along with lava.
Exposed to the oxygen present in air and sparked by lava, the sulfuric gases burn readily, and their flames are bright blue. Some of the sulfuric gases also condense to become liquid sulfur, flowing down the rock face as they burn, making it seem as though blue lava is spilling down the mountainside. This effect is only visible at night – during daytime, the volcano looks like roughly any other.
Some people postulate that Mt. Ijen and its blue flames are what hell actually looks like. In some religious scriptures, hell is described as "one of fire and brimstone". And brimstone, by the way, is an alternative name for sulfur. So... if these scriptures are true, that ain't too far-fetched a theory. Hell, if it exists at all, could really be pitch-black and iridescent blue... and perhaps smell like rotten eggs.
The troubling truth behind the volcano that burns blue
While some of us may view Mt. Ijen as a mere cross off our bucket list, the entire livelihood of many locals depend on it.
Sulfur is a valuable commodity. It has become essential to many products bought and sold across the globe – matches, car batteries, fertilisers, detergent and gunpowder, to name a few. When the volcano's sulfuric gases hit the cooler air outside, they condense into liquid and drip off the pipe. As the liquid cools, it solidifies into yellow sulfur, which can then be chipped off and collected.
Many local sulfur miners depend on this sulfur to support their families and children. Their work is literally back-breaking – When they are on the job, the workers carry the load some 9,000 feet, going up a steep mountain to the crater’s edge. As most miners cannot afford gas masks, they use wet towels to cover their faces, but clouds of toxic sulfur continue to engulf them. Enveloped in poisonous fumes and heat, they chip away at hardended blocks and carry 60-100 kg worth of loads up and down the crater, all to earn a meagre $10 to $15 USD a day. Still, it remains one of the highest paid occupations in the region.
The miners suffer from skin problems and respiratory issues – they cough, their eyes water, and many of them don't live past 50 years old. As if we haven't made enough references to hell, this solid sulfur is aptly named "Devil's gold" by the locals. Perhaps because of its distinct yellow colour, but perhaps because the people who rely heavily on it for money pay a heavy price with their health.
Brings a whole new meaning to making a deal with the devil.
Learn more here about Kawah Ijen and its sulfur-mining industry in this video:
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