Transition Metals - Iandalgleish.co.uk

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ADVANCED HIGHER 6 TransMets1,2-Diaminoethane is a bidentate ligand with two donor sites e.g.NHHCH 2CH 2H HNHHCH 2CH 2NNi 2+N Tri 1,2-diaminoethane nickel(II)HHNHHH 2CNHH 2CHIn octahedral complexes like the hexaaquacopper(II) ion theligands approach the central metal ion along the x, y and z axesrepelling electrons in the d x 2 -y 2 and d z2 orbitals which liedirectly along the x, y and z axes. Thus the energies of thed x 2 -y 2 and d z 2 orbitals are increased relative to the d xy , d yz andd xz orbitals which lie between the x, y and z axes :d x 2- y 2d z 2∆dxydxzdyzIn Cu2+(H 2 O) 6 ∆ = 2.6 x 10-19 kJ. This corresponds to a wavelengthof 764 nm (red light). When red light of wavelength 764 nm strikesthe Cu2+(H 2 O) 6 ion an electron in the lower levels (d xy , d yz andd xz ) is promoted into the higher levels (d x 2 -y 2 and d z2) and redlight is absorbed ; all other colours are transmitted. We candeduce the resulting colour (cyan) using the colour triangle :RYMGCB
ADVANCED HIGHER 7 TransMetsUltra Violet and Visible SpectroscopyAn Ultra violet/Visible spectrometer can be used to measure thewavelength and intensity of the light absorbed:100200 - 400 nm UV400 - 800 nm VIS% transmittance500200 400 600 800λ/nmvariable wavelengthUV/VIS sourcesample incuvettephotocellscreen display ofspectrumAs the wavelength is increased from 200 nm the instrument measuresthe intensity of the light passing through the sample and hittingthe photocell detector. The percentage of the light transmittedthrough the sample is recorded. When no absorption occurs the %transmittance is close to 100%.A solution containing hexaaquacopper(II) ions would absorb at764 nm. When the variable wavelength source reaches 764 nm thesolution would absorb some of the light causing a drop in the %transmittance. The more light absorbed the lower the %transmittance and the bigger the peak. The amount of lightabsorbed depends on the concentration of the solution and cantherefore be used to measure solution concentration.
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