Questions
Answers
The following information is needed for you to be able to answer the question.
- Planck’s constant is 6.63×10-34
- The speed of light is 3×108
- A Cobalt (II) ion red. State three ways that the colour of the complex can be changed without change the element in the centre of the complex.
- Copper (II) sulfate is coloured whereas copper (I) oxide is not.
- State the electron configuration of the copper ions in the two compounds.
- Explain using the electron configurations why copper (II) ions are coloured whereas copper (I) ions are not.
- Copper (II) ions are blue. Explain why this is the case.
- Copper ions in a hexaaquacopper (II) complex absorb light of a wavelength of 810nm. Given that the energy of a 3d electron in copper (II) is 2.20×10-19 J, calculate the energy of the excited electron.
- Explain why a ligand substitution reaction forming in the formation of [Cu(NH3)4(H2O)]2+ results in a different coloured solution.
- Hexaaquairon(II) and hexaaquairon(III) are both coloured complexes.
- Explain why they have different colours when dissolved in water.
- Nitric acid is added to the iron (III) solution, resulting in a colour change. Explain why this occurs.
- The iron (II) complex absorbs light with a wavelength of 365nm. Calculate the energy gap between the ground state d orbital electrons and the excited electrons in kJmol-1The iron (III) complex has an energy gap of 190 kJmol-1 when it absorbs visible light. Use the colour wheel to determine the colour that it should appear.
- The following complexes appear to be the following colours. Use the colour wheel to predict the energy gap between the ground state d-orbital electrons and the excited electrons when the complexes absorb light.
- [Ni(H2O)6]2+ is green.
- [Ni(NH3)4(H2O)2]2+ is blue-green.
- [Ni(NH3)6]2+ is blue.
- [Cr(OH)6]3- is purple.
- The energy gaps for the following complexes are given. State the colour that it will appear.
- [Cr(H2O)6]2+ has an energy gap of 185.70 kJmol-1.
- [Cr(H2O)6]3+ has an energy gap of 204.75 kJ mol-1.
- [CoCl4]2- has an energy gap of 200.30 kJ mol-1.
The following information is needed for you to be able to answer the question.
- Planck’s constant is 6.63×10-34
- The speed of light is 3×108
- A Cobalt (II) ion red. State three ways that the colour of the complex can be changed without change the element in the centre of the complex.
Ligand
Oxidation State
Co-ordination number - Copper (II) sulfate is coloured whereas copper (I) oxide is not.
- State the electron configuration of the copper ions in the two compounds.
Cu2+: [Ar]3d9
Cu+: [Ar]3d10 - Explain using the electron configurations why copper (II) ions are coloured whereas copper (I) ions are not.
Copper (II) ions have unfilled orbitals in the d subshell. This means that electrons from a lower energy orbital in the d-subshell can be excited to the unfilled d-subshell orbitals. Copper (I) ions have a full d-subshell and therefore the electrons cannot be excited from a low energy d-subshell orbital to a high energy d-subshell orbital. - Copper (II) ions are blue. Explain why this is the case.
Copper absorbs red OR red / orange light. All the other frequencies of light are transmitted / reflected. This remaining wavelengths of light produce a blue colour. - Copper ions in a hexaaquacopper (II) complex absorb light of a wavelength of 810nm. Given that the energy of a 3d electron in copper (II) is 2.20×10-19 J, calculate the energy of the excited electron.
Wavelength of light absorbed in m: 5.98×10-7 m
Frequency of light absorbed: c / 5.98×10-7 = 5.02×1014 m-1
Energy of the light absorbed: 5.02×1014 x 6.63×10-34 = 3.326×10-19J
Excited electron energy: 3.326×10-19 + 2.20×10-19 = 5.53E-19 J - Explain why a ligand substitution reaction forming in the formation of [Cu(NH3)4(H2O)]2+ results in a different coloured solution.
Different ligands result in d-orbitals that have different amount of energy. This results in different energy gaps and therefore different wavelengths of light are absorbed. This results in a different colour.
- State the electron configuration of the copper ions in the two compounds.
- Hexaaquairon(II) and hexaaquairon(III) are both coloured complexes.
- Explain why they have different colours when dissolved in water.
Different oxidation number result in d-orbitals that have different amount of energy. This results in different energy gaps and therefore different wavelengths of light are absorbed. This results in a different colour. - Nitric acid is added to the iron (III) solution, resulting in a colour change. Explain why this occurs.
The Iron (III) solution is very acidic. This means that the water ligands react with water molecules in the following way.
[Fe(H2O)6]3+ + H2O ⇌ [Fe(H2O)5(OH)]2+ + H3O+
OR [Fe(H2O)6]3+ ⇌ [Fe(H2O)5(OH)]2+ + H+
By adding nitric acid, the equilibrium shifts towards the left, change the ligands present.
Different ligands result in d-orbitals that have different amount of energy. This results in different energy gaps and therefore different wavelengths of light are absorbed. This results in a different colour. - The iron (II) complex absorbs light with a wavelength of 365nm. Calculate the energy gap between the ground state d orbital electrons and the excited electrons in kJmol-1
Wavelength of light absorbed in m: 3.65×10-7 Frequency of light absorbed: c / 3.65×10-7 = 8.22×1014 m-1
Energy of the light absorbed: 8.22×1014 x 6.63×10-34 = 5.449×10-19 J
In kJ mol-1: (5.449×10-19 x 6.022×1023)/1000 = 328 kJmol-1 - The iron (III) complex has an energy gap of 190 kJmol-1 when it absorbs visible light. Use the colour wheel to determine the colour that it should appear.
Energy gap in J: (190 / 6.022×1023)x1000 = 3.155×10-19 J
Frequency of light: 3.155×10-19 / 6.63×10-34
Wavelength of light: x / 6.63×10-34 = 6.30×10-7 m
Wavelength of light in nm: 630 nm.
Colour: Orange-Red
- Explain why they have different colours when dissolved in water.
- The following complexes appear to be the following colours. Use the colour wheel to predict the energy gap between the ground state d-orbital electrons and the excited electrons when the complexes absorb light.
- [Ni(H2O)6]2+ is green.
Wavelength of light absorbed in nm: 410
Wavelength of light absorbed in m: 4.10×10-7
Frequency of light absorbed: 7.32×1014
Energy of the light absorbed: 4.851×10-19
In kJ mol-1: 292 kJ mol-1 - [Ni(NH3)4(H2O)2]2+ is blue-green.
Wavelength of light absorbed in nm: 645
Wavelength of light absorbed in m: 6.45×10-7
Frequency of light absorbed: 4.65×1014
Energy of the light absorbed: 3.084×10-19
In kJ mol-1: 1856 kJ mol-1 - [Ni(NH3)6]2+ is blue.
Wavelength of light absorbed in nm: 600
Wavelength of light absorbed in m: 6.00×10-7
Frequency of light absorbed: 5.00×1014
Energy of the light absorbed: 3.315×10-19
In kJ mol-1: 199.63 kJ mol-1 - [Cr(OH)6]3- is purple.
Wavelength of light absorbed in nm: 585
Wavelength of light absorbed in m: 5.85×10-7
Frequency of light absorbed: 5.13×1014
Energy of the light absorbed: 3.400×10-19
In kJ mol-1: 204.75 kJ mol-1
- [Ni(H2O)6]2+ is green.
- The energy gaps for the following complexes are given. State the colour that it will appear.
- [Cr(H2O)6]2+ has an energy gap of 185.70 kJmol-1.
Energy gap in J: 3.084×10-19
Frequency of light: 4.651×1014
Wavelength of light: 6.45×10-7
Wavelength of light in nm: 645.01
Colour: Blue-green - [Cr(H2O)6]3+ has an energy gap of 204.75 kJ mol-1.
Energy gap in J: 3.400×10-19
Frequency of light: 5.128×1014
Wavelength of light: 5.85×10-7
Wavelength of light in nm: 584.99
Colour: Purple - [CoCl4]2- has an energy gap of 200.30 kJ mol-1.
Energy gap in J: 3.326×10-19
Frequency of light: 5.017×1014
Wavelength of light: 5.98×10-07
Wavelength of light in nm: 597.99
Colour: Blue
- [Cr(H2O)6]2+ has an energy gap of 185.70 kJmol-1.