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The structures of two aqueous iron complexes are represented in the diagram - HSC - SSCE Chemistry - Question 36 - 2011 - Paper 1
Question 36
The structures of two aqueous iron complexes are represented in the diagram. 1. **Green (Fe^{2+})**: [Fe(H₂O)₆]^{2+} 2. **Yellow-brown (Fe^{3+})**: [Fe(H₂O)₆]^{3+... show full transcript
Worked Solution & Example Answer:The structures of two aqueous iron complexes are represented in the diagram - HSC - SSCE Chemistry - Question 36 - 2011 - Paper 1
Step 1
Account for the different colours of the complexes.
Answer
The different colors of the iron complexes arise due to the varying oxidation states of iron and the nature of the ligands attached to it.
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Green Complex ([Fe(H₂O)₆]^{2+}): This complex contains iron in the +2 oxidation state. The coordination with six water molecules leads to lower crystal field splitting, and therefore, the complex absorbs light in the red region, appearing green.
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Yellow-brown Complex ([Fe(H₂O)₆]^{3+}): In this case, the iron is in the +3 oxidation state. The increase in positive charge results in a stronger field splitting among the d-orbitals, leading to absorption of higher energy light, which corresponds to the violet to blue regions of the spectrum, hence the yellow-brown color observed.
Step 2
Identify ONE cation and ONE anion that can be represented by the electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶.
Answer
One suitable cation is sodium (Na^{+}), which is formed by the loss of one electron from the neutral sodium atom. The corresponding anion could be chloride (Cl^{-}), which is formed when a chlorine atom gains an electron, achieving the same electron configuration as argon.
Step 3
Explain the fact that Group I and Group II metal ions have one oxidation state while the transition metals often have multiple oxidation states.
Answer
Group I and II metals typically have a single oxidation state due to their electronic configurations.
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Group I Metals (Alkali Metals): These elements have one electron in their outermost shell, leading them to lose that single electron to achieve a stable noble gas configuration, resulting in a +1 oxidation state.
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Group II Metals (Alkaline Earth Metals): These elements have two valence electrons, which they lose to form a stable +2 oxidation state.
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Transition Metals: Unlike the main group elements, transition metals have d-electrons that can participate in bonding, allowing them to lose varying numbers of electrons from different shells. This leads to multiple oxidation states. For example, iron can exist in the +2 and +3 states.
Step 4
Describe a method by which the values in the table may have been obtained.
Answer
A suitable method for obtaining the emission lines involves using a spectrophotometer to measure the wavelengths of light emitted by an element when it returns to a lower energy state. This can be done by:
- Exciting the electrons in the element using heat or electricity.
- Allowing the electrons to relax back to their ground state, emitting photons in the process.
- Directing the emitted light through a prism or diffraction grating to separate the wavelengths.
- Recording the specific wavelengths to populate the table.
Step 5
Draw an energy level diagram that corresponds to the data given.
Answer
The energy level diagram should illustrate four energy levels with transitions corresponding to the wavelengths provided in the table. Label the transitions as:
- Transition to the final common energy level from levels corresponding to 656 nm, 486 nm, 434 nm, and 419 nm respectively.
The diagram should feature arrows indicating the downward transitions, highlighting that energy is released when the electrons fall back to a lower energy state.