Describe the emission spectrum of hydrogen. Outline how this spectrum is related to the energy levels in the hydrogen atom.

Transition elements form complexes such as \({{\text{[Fe(CN}}{{\text{)}}_{\text{6}}}{\text{]}}^{4 - }}\) and \({{\text{[FeC}}{{\text{l}}_{\text{4}}}{\text{]}}^ - }\). Deduce the oxidation number of iron in each of these complex ions.

\({{\text{[Fe(CN}}{{\text{)}}_{\text{6}}}{\text{]}}^{4 - }}\)

\({{\text{[FeC}}{{\text{l}}_{\text{4}}}{\text{]}}^ - }\)

series of lines/lines;

electron transfer/transition between higher energy level to lower energy level / electron transitions into first energy level causes UV series / transition into second energy level causes visible series / transition into third energy level causes infrared series;

convergence at higher frequency/energy/short wavelength;

Allow any of the above points to be shown on a diagram.

\({{\text{[Fe(CN}}{{\text{)}}_6}{\text{]}}^{4 - }} =  + 2\);

\({{\text{[FeC}}{{\text{l}}_4}{\text{]}}^ - } =  + {\text{3}}\);

Award [1 max] if 2+ and 3+, 2 and 3 or II and III stated.

In the emission spectrum of hydrogen some candidates missed stating about convergence at high energy/frequency while some other candidates forgot to write that it is a line spectrum.

The majority of candidates deduced the oxidation number of iron in the complex ions correctly although some candidates still wrote 2+ and 3+ which deprived them of one mark.