Fluorine

 

Fluorine

Chemical formula	F
Atomic Number	9
OTP appearance	yellowish gas
Molar Mass(g/mol)	19
Density(g/cc)	0.0017
Melting Point(°C)	-220
Boiling Point(°C)	-188
NFPA 704	0 4 4 OW

It's worth noting up front that elemental fluorine and hydrofluoric acid are ridiculously dangerous, being highly reactive and highly toxic. Elemental fluorine is rarely required, normal usage is as a fluoride ion. (AlF₃, NaF, KMgF₄) There is an actual term "Fluorine Martyr" to describe the substantial number of scientists who were killed or maimed trying to isolate elemental fluorine.

Uses

Primary

• Powerful halogen
• Essential to many medicines
• Alternative to chlorine for aluminum electrolysis
• Present in most highly resistant plastics (Teflon, PTFE, etc)

Natural Occurrence

• Elemental fluorine does not gnerally occur in nature
  • the lone exception is the mineral antozonite
• Fluorine occurs in the minerals fluorite and fluorapatite.

Hazards

Like chlorine, only many times worse.

• highly reactive and very toxic.
• explosive in the presence of hydrogen gas.

Precautions

It's hopelessly dangerous, but if you must...

• Making containers out of fluorite to start with
• Copper containers can be passivated by controlled exposure to fluorine, forming a passivating layer of copper fluoride

Production

N. B. Hopefully no elemental fluorine will ever be required by this project.

Synthesis

Chemical

1. Produce potassium hexafluoromanganate(IV) by the controlled reduction of potassium permanganate, potassium fluoride, hydrofluoric acid and hydrogen peroxide. This is really Manganese(IV) fluoride with two potassium fluorides added on.

   2 KMnO₄ + 2 KF + 10 HF + 3 H₂O₂ → 2 K₂MnF₆ + 8 H₂O + 3 O₂

2. Produce Antimony pentafluoride: from bubbling hydrogen fluoride throughantimony pentachloride and

   SbCl₅(l) + 5 HF(g) → SbF₅(l) + 5 HCl(g)

3. Combine potassium hexafluoromanganate(IV) and antimony pentafluoride, producing elemental fluorine

   2 K₂MnF₆(s) + 4 SbF₅(l) → 4 KSbF₆ + 2 MnF₃ + F₂

Electrolysis

1. Combine potassium hydroxide and hydrogen fluoride

   KOH + 2 HF → KHF₂ + H₂O

2. Remove the water
3. Combine with additional hydrogen fluoride

   KHF₂ + HF → KH₂F₃

4. Electrolyze, producing hydrogen and fluorine

   2 KH₂F₃(l)

   {

   →

   -50°C}

   2 KHF₂ + H₂(g) + F₂(g)

Storage

• Elemental Fluorine can be stored in passivated metals and teflon
• More practically, it can be "stored" as mercury (II) fluoride (HgF₂) simply by exposing a mercury halide or oxide to fluorine gas. Mercury (II) fluoride thermally decomposes into Mercury vapor and fluorine at 645°C

  2 HgF₂(s)

  {

  →

  645°C}

  2 HgF(g) + F₂(f) quickly followed (at that temperature) by

  2 HgF(g)

  {

  →

  570°C}

  2 Hg(g) + F₂ which represents complete dissociation into gaseous mercury and fuorine.

• Cooling these gases below 350°C condenses the mercury leaving the fluorine

See Also

• Fluorine minerals sodium aluminum hexafluoride, fluorapatite and fluorite.