Cobalt is one of the three metals in the first transition series that is ferromagnetic (magnetic) - VCE - SSCE Chemistry - Question 8 - 2003 - Paper 1
Question 8
Cobalt is one of the three metals in the first transition series that is ferromagnetic (magnetic). Give the name or symbol of the other two ferromagnetic metals in t... show full transcript
Worked Solution & Example Answer:Cobalt is one of the three metals in the first transition series that is ferromagnetic (magnetic) - VCE - SSCE Chemistry - Question 8 - 2003 - Paper 1
Step 1
Give the name or symbol of the other two ferromagnetic metals in the first transition series.
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Answer
The two other ferromagnetic metals in the first transition series are iron (Fe) and nickel (Ni).
Step 2
i. Sketch the structure for Co(NH₃)₆³⁺.
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Answer
The structure of Co(NH₃)₆³⁺ can be represented as a cobalt ion (Co³⁺) at the center, surrounded by six ammonia (NH₃) ligands arranged octahedrally. Each NH₃ molecule donates a lone pair to the cobalt ion.
Step 3
ii. Name the type of bonding that exists
- between Co²⁺ ion and the NH₃ molecules
- within the NH₃ molecule
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Answer
Between Co²⁺ and the NH₃ molecules, the type of bonding is ion-dipole bonding. Within the NH₃ molecule, the bonding is covalent.
Step 4
Suggest a reason why NH₃ might bond more firmly to Co²⁺ than to Co²⁺.
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Answer
NH₃ might bond more firmly to Co²⁺ than to Co²⁺ due to the higher charge density of Co²⁺ which creates a stronger attractive force, thus facilitating a more stable interaction with the ammonia molecules.
Step 5
i. Select two of the above half reactions which together indicate that, in aqueous solution, NH₃ bonds to Co²⁺ rather than to Co²⁺.
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Answer
The selected half reactions are: 1) Co(H₂O)₆²⁺ + 2e⁻ → Co(s) + 6H₂O with E° = -0.28 V and 3) Co(NH₃)₆²⁺ + 2e⁻ → Co(s) + 6NH₃ with E° = -0.56 V. This indicates that NH₃ bonds preferentially to Co²⁺.
Step 6
ii. Explain, using the above data, why aqueous solutions containing Co(H₂O)₆³⁺ might be too unstable to be conveniently used in the laboratory.
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Answer
Co(H₂O)₆³⁺ is prone to hydrolysis and can spontaneously transfer electrons to form less stable compounds. This reaction indicates that Co(H₂O)₆³⁺ will react with water, which can lead to a decrease in concentration of Co(H₂O)₆³⁺ in solution, making it unstable for laboratory use.
