Humidity Indicator (1 Viewer)

[Sirius Black]

Hello all, as you l\know, Blue CoCl4^2-+6H2O<-->Co(H2O)6²⁺+4Cl-
hmm does anyone can figure out the valence charge of Co in pink Co(H2O)6²⁺ for me plz?
Ta

 

[xiao1985]

2+ ? since water is neutral?!

 

[Sirius Black]

If it is 2+, why would they bother writing like Co(H2O)6²⁺ rather than Co2+ .6H2O?(altho I've never seen such a formula like this b4)

 

[funking_you]

This is what we call a 'complex'
Please excuse the irony of the name, however 'complex's are a VERY common (and simple - yes i know that is now a pun), type of metallic compound.

• Which elements form complex's?
  Transition metals!

• What makes up a complex?
  A transition metal in the centre, with 'ligands' bonded to it directly via chemical bonds

• What is a ligand?
  A 'ligand' is any species that contains (at least) one lone pair of electrons, i.e. a pair of electrons that are NOT involved in chemical bonds, so H₂O, contains a lone of pair electrons (draw its lewis structure and you will see for yourself)

• Can any of you come up with other 'ligands'?

So this example, Co(H₂O)₆²⁺, we have a cobalt cation in the middle of compound, and six water molecules bonded around it (hexagonal geometry)...cool ey!,

If you get a chance again to make the Co(H₂O)₆²⁺, ask your teaching if you can add con. HCl....and you will get a nice blue colour change.

In anwser to your question, the 'charge' or more correctly the oxidation state of cobalt, is calculated in the same way as you would for any other element in a compound. Its oxidation state is 2+, since water is neutral, hence the overall charge of 2+ must come completely from the cobalt.

This is actually all in the HSC syllabus, in the Chemistry of Art Elective, complexes are very interesting and fun, mainly because of their cool colours and geometry



George

 

[xiao1985]

T_T u stole my post goerge!!!

=p
i'd rep u again if i can =S

edit: jsut to contribute sth:
for those who will study moinotirng, the method to quantitatively assess the 'hardness' of the water is to titrate the sample with EDTA (ethylene diamine tetra acetate) which is a chelate (multi toothed) ligand too... =)

@ chem coach: tho i am not entirely sure why enchrome black T is used as an indicator... as in the mechanism how it indicates the concentration ...

is it in a way that the ligands bonds to Mg 2+ and Ca 2+ more strongly than enchrome black T, so when there's excess ligands, it will bond to the indicator hence change it's colour?!