Edexcel Chemistry Unit 5 June 19 2012

why do we need to know about this diagram?

because it's within r syllabus
chromium(ii) ehatnoate is special chromium compound cause normally chromium is stable in compounds when it has and oxi state of +3 ,+6 but chromium(ii) ehatnoate is stable and has a +2 oxi state

the reaction procedure is explained in the attachment

so it's a possible topic to mix with some synoptic questions and ask

this also has many hazards
*solid sodium dichromate is toxic carcinogenic and an irritant
*conc HCl - corrosive
*Zn powder and H2 are highly flammable

Do you guys feel that unit 5 will be better than unit 4? I think that for some reason; the content in unit 4 is more llikely to come up with trricky questions.. i dont think thats the case with unit 5.

Can someone explain to me when we have to use the platinum electrode in the half cells?

thanks

what type of question do they ask in u5? I haven't done any past paper yet....

Guys is this right? Hexa aqua ions are coloured due to promoted electrons falling back to lower energy levels and releasing energy in the visible spectrum.

However where water ligands have been replaced by other ligands, the D-orbital is split and the subsequent d-d electron movement absorb all visible light except a specific colour?

just a quick question:
how much detail do we need to know about 3d sub-shells splitting into 2 energy levels due to ligands?

Ligands cause the metal ion's D orbitals to be split into two energy levels. A higher and lower level. Wavelengths of light with energy the same as that of the difference between energy levels are absorbed and the energy is used to promote electrons from the lower energy level to the higher level (This is a d-d transition). The electrons shortly 'fall back' to the lower level, releasing the energy difference as heat(not light). Hence, the solution appears the complimentary colour to that of the wavelength absorbed.

However, if the D orbitals are full, then promotion cannot take place, and so no light is absorbed -> it appears white. Equally if there are no ligands, there is no splitting of the d orbitals and hence, no absorption can take place.

a lot, i believe. most of the question from the PREVIOUS spec had always a 3-4marks questions on that lol

You need to know that and why the complex appears coloured. Check past paper mark schemes for a more complete answer.

Could you guys link me to some questions or tell me where to find them?

Past question papers; http://www.edexcel.com/quals/gce/gce08/chemistry/Pages/default.aspx

Feeling quite confident on this mainly. Hoping we don't get any questions on the reaction between MnO4- and Cr2O4 because I always drop marks on those and find it hard to rememeber all the different half equations.

Could you guys link me to some questions or tell me where to find them?

x

By the way this is for edexcel... :P

Im not clear about reactions with non-neutral ligands sorry, Have you got a list of which ones we need to kno and be able to write the equations of their ligand exchanges?