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 for Co(NH₃)₆³⁺ can be sketched as Co at the center, surrounded octahedrally by six NH₃ ligands, which are indicated as dots or lines extending from the cobalt ion.
Step 3
ii. Name the type of bonding that exists - between Co²⁺ ion and the NH₃ molecules.
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Answer
The type of bonding between Co²⁺ ion and the NH₃ molecules is coordinate (or dative) covalent bonding. The lone pair of electrons from nitrogen is donated to the metal ion.
Step 4
ii. Name the type of bonding that exists - within the NH₃ molecule.
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Answer
Within the NH₃ molecule, the bonding is covalent, formed by the sharing of electrons between nitrogen and hydrogen atoms.
Step 5
Suggest a reason why NH₃ might bond more firmly to Co²⁺ than to Co²⁺.
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Answer
NH₃ has a higher electron density and forms stronger coordinate bonds with Co²⁺ due to its ability to donate a lone pair of electrons more effectively compared to other ligands.
Step 6
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 half reactions to select are 1 and 3, which illustrate that Co(NH₃)₆²⁺ complexes are formed and indicate bonding preference of NH₃ to Co²⁺.
Step 7
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 likely too unstable because it readily transitions to Co(NH₃)₆²⁺, as indicated by its high E° value, which suggests a spontaneous reaction in the presence of adequate ligands like NH₃, creating a less stable hydrating ion.
