(i) Any two of:

trial 1 was a rapid/rough titration «to find the approximate titre», so the end point was overshot ✔

the jet below the tap was not filled/an air bubble was trapped when the initial reading was taken ✔

the tap was leaking/not closed properly ✔

the conical flask was contaminated/rinsed with the sample «instead of with deionized water» ✔

extra EDTA was added «after the colour change» to check that the end point was complete ✔

(ii) outlier ✔

(iii) including it would make the mean titre «and the calculated concentration» too high ✔

OR

it is not concordant with the other three titres «it differs from them by more than 0.10 $\mathrm{cm^3}$» ✔

OR

it would introduce a systematic error into the mean ✔

(iv) «$\dfrac{2 \times 0.05}{22.25} \times 100 =$» 0.45 «%» ✔

(v) X/yellow complex absorbs violet light/its complementary colour/light of 400-424 nm AND Y/violet ion absorbs yellow light/its complementary colour/light of 575-585 nm ✔

violet light has a shorter wavelength/higher frequency «and therefore higher energy, $E = hf$» than yellow light ✔

(i) [2 max], list principle: any two distinct reasons. (ii) [1]; accept anomalous result or anomaly. (iii) [1] for any one reason. (iv) [1] for 0.45 % or 0.4 %; the uncertainty of a titre is 0.10 cm3 because two burette readings are subtracted, so 0.22 % from a single reading scores 0. (v) M1: the two complementary colours absorbed, both needed, wavelengths not required; M2: the comparison of wavelength or frequency or energy of violet and yellow light; accept the converse argument written for Y.