Salt formers

Last time I asked “What do you predict would happen to a bunch of brightly coloured flowers placed into a gas jar of chlorine?” Well, of course, the flowers would be bleached white and this is indeed what happened.

Bleach them white

Bleach them white

Chlorine is an element in Group 7 of the Periodic Table, a group called The Halogens. The halogens are: F = fluorine, Cl = chlorine, Br = bromine, I = iodine and At = astatine.

Salt formers

Salt formers

The elements exist as diatomic molecules and we had some fun doodling this the other day.

Hand in hand

Hand in hand

Britannica.com says “the name halogen, from the Greek roots hal- (“salt”) and -gen (“to produce”).” Thus, the halogens produce salts and in my blog of November 1st 2012 I showed some pictures of sodium chloride, sodium bromide and sodium iodide. I don’t have any sodium fluoride, but this too should be a white, crystalline solid.

Sodium fluoride is toxic if swallowed and liberates very toxic gas on contact with acids (CLEAPSS Hazcard 95A, 2007). Presumably this could happen in the stomach if large amounts were ingested. Fortunately, only very small amounts of sodium fluoride are added to fluoride toothpaste (for example 0.32% w/w). Probably best not to swallow your toothpaste anyhow, just in case!

The formula for sodium fluoride is NaF, what would be the formula of calcium fluoride?

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Bleach

Chlorine has a characteristic smell and it also bleaches things white. Thus, you soon know if you have any chlorine around by its whiff and by testing for its bleaching properties. It has a pale yellow/green colour, although this can be hard to see at low concentrations.

A gas jar filled with chlorine gas

A gas jar filled with chlorine gas

Chlorine bleaches both red and blue litmus paper white. For the animation below the litmus papers were moistened with distilled water and attached to a glass rod before being lowered into chlorine.

Moist red and blue litmus turn white

Moist red and blue litmus turn white

It’s possible to see the blue litmus paper turning pink, before it is bleached white. This is because as the chlorine gas dissolves in water it reacts to produce both hypochlorous acid (HOCl) and hydrochloric acid (HCl).
Cl2 + H2O -> HOCl + HCl
Hypochlorous acid is the active disinfectant in water treatment and this is one of the most important technologies used in industrialised societies. Of course, chlorine gas is quite toxic and humans should avoid inhaling it, especially those with known breathing difficulties such as asthma.
What do you predict would happen to a bunch of brightly coloured flowers placed into a gas jar of chlorine?