When An Essential Substance Used In Chemistry Turned Out Not To Exist

In 2018, a team of researchers attempting to investigate the use of sulfide solutions to reduce mercury emissions from alumina refineries made another, bigger discovery: an ion once considered an essential part of chemistry calculations simply does not exist.

While investigating the use of sulfide solutions to reduce mercury emissions, the team began looking at the S^2– ion. While it does exist in various forms, it had been assumed that it exists as an aqueous solution, with water acting as the dissolving substance. 

For decades, it was assumed that it existed in this form, S^2–(aq). However, the team used a Raman spectrometer, which uses scattered light to measure the vibrational energy modes of samples, and found to everyone’s surprise that despite their best efforts no S^2–(aq) was detected.

“A simple chemical problem that defies the best that modern instrumentation can provide is rare nowadays,” the team wrote in their paper. “A widespread, ongoing misadventure in science is even rarer. However, both have happened over the assumed existence of the chemical species S^2–(aq).”

According to the team, who wrote that the ion (in aqueous form) needs to be “comprehensively banished by the chemical community”, the mistake took place decades ago, and has been a part of chemistry research calculations ever since.

“It means that some simple chemistry calculations, often used to predict how sulfide minerals dissolve and react in water, are incorrect,” Dr Darren Rowland, co-author on the study, said in a statement at the time. “Our recommendation to researchers and teachers is to not accept the existence of sulfide ion in aqueous solution, as there is no evidence for its existence.”

“We hope our results now take a firm hold in chemical calculations,” he added, “but time will tell.”

The study is published in Chemical Communications.