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1 markUltra Violet-Visible (UV/VIS) Spectroscopy

CAPE Chemistry Unit 2 · May/June 2025 · Paper 2 · Question 2(d)(ii)

An experiment is carried out to determine the concentration of Cu2+ ions in a sample of well water. A measured volume of the water is treated with excess ammonia and a sample of the resultant solution was analysed in a cuvette, of side 1 cm, at a wavelength of 615 nm in a UV/VIS spectrophotometer.

Give the reason why the wavelength of 615 nm was chosen.

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Other parts of this question

  1. 2(a)Draw a diagram to show the approximate wavelength ranges of any THREE types of radiation which are found in the electromagnetic spectrum.[3 marks]
  2. 2(b)The energy of an electronic transition has a frequency of 1.01 × 10^16 Hz. Calculate the energy of the radiation emitted.[2 marks]
  3. 2(c)On Figure 3, draw the possible transitions associated with the absorption in this UV/VIS region of the spectrum.[3 marks]
  4. 2(d)(i)State what would be observed when the ammonia is added.[1 mark]
  5. 2(d)(iii)Describe how a calibration curve can be made and used in the analysis process.[3 marks]
  6. 2(e)(i)Calculate the concentration of the known Cu2+ ions, in mol/dm^3.[3 marks]
  7. 2(e)(ii)Applying Beer-Lambert's law, calculate the molar absorptivity using the stated absorbance value.[3 marks]
  8. 2(e)(iii)Calculate the concentration of the Cu2+ ions in this sample.[1 mark]
  9. 2(f)Outline the steps in analysing a sample using UV/VIS spectroscopy.[4 marks]
  10. 2(g)Explain the principles of infrared spectroscopy.[2 marks]
  11. 2(h)(i)Compound D exhibits characteristic absorption wave numbers 1695 cm^-1 and 1619 cm^-1 in the infrared spectrum. Indicate the functional groups responsible for…[2 marks]
  12. 2(h)(ii)Indicate TWO types of vibrations that could be exhibited by Compound D.[2 marks]

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