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Transition metals (A-level only)

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Question 9

The nickel content of a sample of industrial electroplating rinse-water can be determined using colorimetric analysis.

Method:

  • A 25.0 cm3 sample of rinse-water is treated with excess concentrated aqueous ammonia to convert all nickel(II) ions into the blue-violet complex ion, [Ni(NH3)6]2+[\text{Ni}(\text{NH}_3)_6]^{2+}[Ni(NH3​)6​]2+.
  • The mixture is made up to 250 cm3 with distilled water in a volumetric flask.
  • This complex absorbs light strongly at a wavelength of 585 nm585\text{ nm}585 nm.
  • The absorbance of the solution is measured at 585 nm585\text{ nm}585 nm and a calibration graph is used to find the concentration of the nickel complex.

Questions:

a.

Calculate the energy, in J\text{J}J, gained by each excited electron in the absorption of light at 585 nm585\text{ nm}585 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)

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b.

The concentration of the nickel complex in the 250 cm3 volumetric flask is determined to be 5.24 × 10-3 mol dm-3. Calculate the mass, in mg\text{mg}mg, of nickel in the original 25.0 cm3 sample. (Relative atomic mass, Ar(Ni)=58.7A_r(\text{Ni}) = 58.7Ar​(Ni)=58.7)

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Transition metals (A-level only) Questions

  1. A Level
  2. /Chemistry
  3. /Transition metals (A-level only)