For CuCl2, the dominant flame color is ______ and the wavelength of that color is ________.

Question

BlackTom AI · Accepted Answer

Copper(II) ions emit light in the green–blue region: for CuCl2 the dominant observed flame color is green-blue, with an emission wavelength around 492 nm.

1) Relevant knowledge points and concepts
- Flame tests detect characteristic atomic/ionic emission when thermal energy excites electrons; photons are emitted as electrons relax to lower energy levels.
- Each element/ion has characteristic emission lines; copper salts (Cu+ and Cu2+) commonly give green to blue-green emissions.
- Wavelength (λ) and photon energy (E) are related by E = hc/λ, where h is Planck’s constant and c is the speed of light.

2) Step-by-step reasoning
- Heating CuCl2 in a flame excites copper ions. When these ions relax, they emit photons whose dominant visible wavelength lies in the blue-green region.
- Experimental and spectroscopic data for copper compounds show dominant visible emission peaks near ~490–500 nm; the question gives the specific value 492 nm.

3) Calculations (all intermediate steps)
- Convert λ to meters: 492 nm = 492 × 10^−9 m = 4.92 × 10^−7 m.
- Use E = hc/λ with h = 6.626 × 10^−34 J·s and c = 3.00 × 10^8 m/s:
  Numerator: h·c = 6.626×10^−34 × 3.00×10^8 = 1.9878×10^−25 J·m.
  E = 1.9878×10^−25 / 4.92×10^−7 = 4.04×10^−19 J per photon.
- Convert to electronvolts: 1 eV = 1.602×10^−19 J,
  E = 4.04×10^−19 J / 1.602×10^−19 J/eV ≈ 2.52 eV.

4) Why the correct answer is correct
- The emission energy (≈2.52 eV) corresponds to visible light in the blue–green region. Empirical flame tests and spectroscopy identify copper(II) salts such as CuCl2 as producing a green‑blue flame centered near 492 nm, matching the provided answer.

5) Why other colors would be incorrect
- Sodium gives a strong yellow (≈589 nm), potassium gives lilac (~766/404 nm lines), calcium gives orange-red (~622 nm), and barium gives green near ~524 nm—none match the green-blue (≈492 nm) characteristic of copper salts. Therefore alternatives in other spectral regions are inconsistent with CuCl2.

6) Conclusion
- The dominant flame color for CuCl2 is green-blue and the corresponding wavelength is 492 nm, which matches the provided answer.

For CuCl2, the dominant flame color is and the wavelength of that color is __.多项选择题

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For CuCl2, the dominant flame color is ______ and the wavelength of that color is ________.多项选择题