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Transition metals (A-level only)

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Question 17

The titanium content of an industrial acidic effluent sample can be determined using colorimetric analysis.

Method:

  • A sample of the effluent is treated to ensure all titanium is present as the purple titanium(III) complex ion, [Ti(H2O)6]3+[\text{Ti}(\text{H}_2\text{O})_6]^{3+}[Ti(H2​O)6​]3+.
  • The solution is diluted to exactly 250 cm3250\text{ cm}^3250 cm3 with distilled water in a volumetric flask.
  • This complex absorbs light strongly at a wavelength of 510 nm510\text{ nm}510 nm due to ddd-ddd electron excitation.
  • The absorbance of the solution is measured at 510 nm510\text{ nm}510 nm and a calibration curve is used to determine the concentration of the complex.

Questions:

1.

Calculate the energy, in J\text{J}J, gained by each excited electron during the absorption of light at 510 nm510\text{ nm}510 nm. (Speed of light, c=3.00×108 m s−1c = 3.00 \times 10^8\text{ m s}^{-1}c=3.00×108 m s−1; Planck constant, h=6.63×10−34 J sh = 6.63 \times 10^{-34}\text{ J s}h=6.63×10−34 J s)

[3]
2.

The concentration of the titanium complex in the 250 cm3250\text{ cm}^3250 cm3 solution is determined to be 1.65×10−3 mol dm−31.65 \times 10^{-3}\text{ mol dm}^{-3}1.65×10−3 mol dm−3. Calculate the mass, in mg\text{mg}mg, of titanium in the original sample. (Relative atomic mass, Ar(Ti)=47.9A_r(\text{Ti}) = 47.9Ar​(Ti)=47.9)

[3]

Transition metals (A-level only) Questions

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