halogens

A small cylinder of hydrogen fluoride with 340 g or 360 liter of HF in it. More than enough to kill someone. 

Hydrogen fluoride is a colorless gas what can be liquefied quite easily, with a little ice and water, since its boiling point is 19.5 °C. The gas or its solution in water (hydrofluoric acid) attacks glass, so it could be only stored in steel or plastic. The reaction with silicates (glass) produces silicon tetrafluoride what is a low boiling point ( 4 °C), highly reactive compound and hexafluorosilicic acid.

SiO2 + 4 HF → SiF4(g) + 2 H2O
SiO2 + 6 HF → H2SiF6 + 2 H2O

Hydrogen fluoride is the only hydrohalic acid that is not considered a strong acid, i.e. it does not fully ionize in dilute aqueous solutions. When the concentration of HF approaches 100% (like in the gas cylinder on the picture), the acidity increases dramatically because of homoassociation: 3 HF is in equilibrium with H2F+ +  FHF−

Once absorbed into blood through the skin, it reacts with blood calcium and may cause cardiac arrest. In the body, hydrofluoric acid reacts with the ubiquitous biologically important ions Ca2+ and Mg2+. Hydrofluoric acid exposure is often treated with calcium gluconate, a source of Ca2+ that sequesters the fluoride ions. So if anyone works with this, always have a lot calcium gluconate solution somewhere close.

8/9/14 Collin’s Garage with @onyourmarksnj @crosstowntrain @northrunner_ @gin_war & #halogens

📷: @angieenicoleee (at Suffern, New York)

There is a rule, that elemental iodine dissolves in oxygen containing solvents with brown and oxygen free solvent with purple color. 

Well, in this case I dissolved some iodine in trimethyl-borate, methyl ester of boric acid (B(OMe)3) and got this reddish solution. It’s far from brown and it’s not purple.

P.S.: Yes, I know I should wear gloves, but currently we do not have any gloves in the lab… 

Halogens

Trends

  • reactivity, electronegativity, mpt, bpt, all increase up the group  because the ionic radius is smaller up the group, as there is less shielding, so the attraction between the electrons and nucleus will be stronger towards the top
  • the solubility increases up the group because they are more electronegative and polar, so can overcome the forces of the hydrogen bonds in water. note that fluorine also exhibits hydrogen bonding.
  • they look darker and become more volatile down the group, this is because there will be more electrons in the elements towards the bottom, so they will have stronger intermolecular forces. this is why iodine is a solid, bromine, a liquid, and chlorine and fluorine are gases.
  • become stronger reducing agents as you go down

Reactions

  • with hydrogen H2 + X2 —-> 2HX
    chlorine needs dark
    bromine needs a platinum catalyst at high temperature
    iodine needs a platinum catalyst at a high temperature 
  • hydrogen halide + ammonia gas —-> ammonia halide
  • halogen + sulphuric acid ——> hydrogen halide (they are oxidised)
    chlorine= steamy fumes (HCl)
    bromine= misty fumes and red/ brown vapour (HBr)
    iodine= violet fumes (HI)
  • potassium halide + Cl2 —-> potassium chloride + halogen
  • disproportionation reactions with alkali

Tests 

add dilute nitric acid and aqueous silver ammonia.

  • chlorides= white ppt
  •  bromides = cream ppt
  • ioides = pale yellow ppt

to that ppt, add dilute, then concentrated ammonia

  • AgCl= dissolves in dilute ammonia
  • AgBr= only dissolves in concentrated ammonia
  • AgI = does not dissolve in any
snippet one: fluorine

fluorine explodes into the room, yelling about some nonsense or another. i make a spirited attempt to ignore her. she is too damn perky and it is too damn early. i turn another page of my book, hoping she would see reason and leave me the hell alone. no such luck.

'did you even listen to anything i just said?! stop reading that dumb book, you can read that dumb book any time, but what you can’t do is listen to me any time, because i’m only going to say this once more and then i’ll never say it again. never ever ever again.’

i thumb another page and scan the words with passionate and focused intent. she flicks her short blonde hair and fixes her piercing, searching eyes on me.

'astatine, you cold and heartless cow, can you not just humour me for a mere six seconds? if it weren't for all our other sisters, i'd be your only sister and if i died, you'd live on never knowing what i, your only sister, would have said…' she lets out an almost-convincing sigh. i admit defeat.

'… you have six seconds'

she takes a deep breath and i brace for impact.

'i need money'