40 Fun Facts About Chlorine

The so-called chlorine smell at swimming pools actually comes from which compound, formed when chlorine meets sweat?

Chloramine forms when free chlorine reacts with compounds in sweat and other body waste, so the famous pool smell is not the element itself.

Soldiers gassed with chlorine in World War I said it smelled like pepper mixed with which tropical fruit?

Pineapple and pepper was how survivors described the smell, and they also reported a metallic taste that stung the back of the throat.

Before proper gas masks, World War I troops facing chlorine were told to breathe through cloths soaked in what?

Urine was advised because its urea was thought to react with chlorine and blunt it, and the order went down the line within days of the first attack.

Which Hungarian doctor slashed deaths in a Vienna maternity ward by making staff wash their hands in chlorine solution?

Ignaz Semmelweis chose chlorine because it removed the smell of the dissecting room from doctors' hands, which soap alone did not.

Which artificial sweetener, sold under the Splenda brand, is table sugar with three chlorine atoms swapped in?

Sucralose is about 600 times sweeter than sugar, and it was reportedly found when a researcher misheard an order to test a chlorinated compound as taste.

Vinyl records are pressed from which chlorine-rich plastic, also used for water pipes and window frames?

PVC is the world's third most produced plastic, and chlorine makes up more than half of its weight.

What in the human body makes its own hypochlorous acid, the germ-killer in chlorinated pools, to destroy bacteria?

White blood cells called neutrophils turn chloride ions into hypochlorous acid, a bleach-like weapon they use against invading microbes.

The human stomach uses chlorine taken from salt in food to make which corrosive chemical for digestion?

Hydrochloric acid brings the stomach's contents down to a pH between 1 and 3, strong enough to act as a barrier against swallowed microbes.

Which sweet-smelling chlorine compound did Queen Victoria inhale for pain relief during two of her childbirths?

Chloroform was given to the queen by physician John Snow, the same doctor linked to the famous cholera outbreak around London's Broad Street pump.

Chlorine atoms released by CFC gases from old fridges and spray cans destroy which protective part of the atmosphere?

Ozone layer damage is so efficient because each chlorine atom works as a catalyst, breaking up ozone molecules over and over without being used up.

The name chlorine comes from the Greek word khloros, which describes the gas as which colour?

Pale green is the meaning of the Greek khloros, the same root that gives the leaf pigment chlorophyll its name.

Table salt is chlorine bonded to which soft, silvery metal that reacts fiercely with water?

Sodium is a highly reactive metal and chlorine is a poison gas, yet joined together they make a seasoning the body cannot live without.

Chlorine gas made its battlefield debut in April 1915 near which Belgian town on the Western Front?

Ypres was where German troops opened 5,730 cylinders and let the breeze carry the gas across to the Allied lines.

Chlorine, fluorine and iodine belong to which family of elements, whose name is Greek for salt producer?

Halogens was a label first coined for chlorine alone in 1811, and only later stretched to cover its whole column of the periodic table.

Which British chemist, inventor of the miners' safety lamp, proved in 1810 that chlorine was an element?

Humphry Davy repeated an experiment that two French chemists had given up on, decided the gas could not be broken down, and gave it the name it still has.

Which Swedish chemist is credited with discovering chlorine in 1774 but took it for a compound, not a new element?

Carl Wilhelm Scheele made the gas from a manganese mineral and noted that it bleached litmus and killed insects.

Which chlorine-based insecticide was banned in the United States after Rachel Carson attacked it in Silent Spring?

DDT was so prized at first that the Swiss scientist who found its insect-killing power won a Nobel Prize, years before its harm to wildlife came to light.

NASA's Phoenix lander found perchlorate, a chlorine-rich salt toxic to people, in the soil of which world?

Mars has perchlorate spread through its soil, where the salt works like antifreeze and could let briny water stay liquid for a few hours on summer days.

Mixing chlorine bleach with which other common household cleaner produces toxic, lung-burning fumes?

Ammonia reacts with bleach to form poisonous gases, and one of the products, nitrogen trichloride, is explosive as well.

Which chlorine-containing herbicide did American aircraft spray over jungle to strip away cover during the Vietnam War?

Agent Orange blended two chlorinated weedkillers and carried traces of a chlorine-based dioxin, a contaminant linked to cancer.

America's first continuously chlorinated water supply served which community on the Hudson River, facing Manhattan?

Jersey City began treating its Boonton Reservoir supply in 1908, and within a decade the US Treasury was calling for all drinking water to be chlorinated.

Which World War I poison gas, made from chlorine and carbon monoxide, smells faintly of freshly mown hay?

Phosgene was harder to detect than chlorine and far more lethal, and it is blamed for about 85,000 deaths in the war.

Which German chemist, later a Nobel laureate, personally oversaw the first chlorine gas attack of World War I?

Fritz Haber argued that gas was no crueller than bullets, and he is remembered as the father of chemical warfare.

Which British scientist, best known for his work on electricity and magnetism, first turned chlorine into a liquid?

Michael Faraday liquefied chlorine in 1823, and he also discovered tetrachloroethylene, the chlorine-rich liquid that later became a leading dry-cleaning solvent.

Which French chemist first used chlorine gas on cloth and created the bleach known as Javel water?

Claude Berthollet made the liquid in 1789 at his laboratory on the Javel quay in Paris, which is how the bleach got its name.

Which chlorine-bearing acid mixture, known to alchemists for centuries, is famous for dissolving gold?

Aqua regia hid two gold Nobel Prize medals from the Nazis in World War II, when a chemist in Copenhagen dissolved them and left the jar on a shelf.

Which inherited disease is diagnosed with a sweat test measuring chloride, the ion form of chlorine?

Cystic fibrosis damages the channels that move chloride in and out of cells, so far more of it than normal ends up in a patient's sweat.

Which element, a red-brown liquid at room temperature, is used like chlorine to disinfect swimming pools?

Bromine kills germs much as chlorine does but keeps working across a wider pH range, which makes it a good choice for indoor pools.

Which chlorine-containing synthetic rubber, invented at DuPont in 1930, is the usual material for wetsuits?

Neoprene is built from chloroprene, a chlorine-bearing molecule, and the foamed form traps heat well enough to insulate divers and surfers.

Chlorine has caused swimming pool ceilings to collapse by cracking rods made of which normally rust-proof metal?

Stainless steel is not alone in cracking under chlorine attack: the same kind of damage ruined plastic plumbing joints across the US in the 1980s and 1990s.

Outdoor swimming pools lose chlorine quickly because it is broken down by which invisible part of sunlight?

Ultraviolet rays use up free chlorine so fast that pool owners add cyanuric acid, a stabiliser that shields it from the sun.

Which Middle Eastern country's government did international inspectors find had dropped chlorine in barrel bombs?

Syria was blamed by a joint UN and chemical weapons watchdog inquiry in 2016 for three separate chlorine attacks during its civil war.

Early chemists insisted chlorine must contain which element, wrongly believed to be a part of every acid?

Oxygen even takes its name from Greek roots meaning acid producer, a label it kept after chlorine's own acid was shown to contain none.

Splitting brine with electricity yields chlorine, hydrogen and which strong alkali?

Caustic soda and chlorine have to be kept apart inside the cell, because left to mix they react to form bleach.

Raymond Davis filled a tank in a gold mine with chlorine-rich dry-cleaning fluid to catch which particles from the Sun?

Neutrinos showed up at only a third of the predicted rate, a puzzle that lasted decades and earned Davis a share of the 2002 Nobel Prize in Physics.

Chlorine, not fluorine, holds the record among all elements for the highest value of which atomic property?

Electron affinity is the energy an atom gives out on gaining an electron, and fluorine falls short because its atoms are so small.

At which 1915 battle in France did Britain's first chlorine gas attack drift back onto its own troops?

Loos lies in a hollow, and in a light, shifting breeze part of the gas cloud eddied back over the British lines.

A typhoid epidemic in which English cathedral city was stopped in 1905 by adding chlorine to the water supply?

Lincoln kept treating its water as a precaution until 1911, which is why it counts as the start of permanent water chlorination.

Which chlorine-based wound wash, named after a British chemist, was developed at a World War I field hospital?

Dakin's solution is a weak bleach, and a modified version still rinses wounds infected with bacteria that resist antibiotics.

A chlorine-rich perchlorate salt was the oxidiser in the twin solid rocket boosters of which NASA spacecraft?

Space Shuttle boosters were the most powerful solid rocket motors ever flown when they debuted, and perchlorate made up about 70% of their propellant by weight.