[3.2.6] Reactions of Ions in Aqueous Solutions Flashcards
What is a Lewis acid and what is a Lewis base?
- Lewis acid: electron pair acceptor.
- Lewis base: electron pair donator.
In the formation of complex ions, is the ligand a Lewis acid or base?
- Lewis base because it donates a pair of electrons in the dative covalent bond and the metal ion is the Lewis acid.
In an aqueous solution, what metal-aqua ions are formed, limited to Fe, Cu and Al.
What colour are these ions?
- [M(H₂O)₆]²⁺, limited to M = Fe (green) and Cu (blue).
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[M(H₂O)₆]³⁺ limited to M = Al (colourless) and Fe (violet).
- In solution, Fe³⁺ appears yellow/brown.
Explain in terms of the charge/size ratio of the metal ion, why the acidity of [M(H₂O)₆]³⁺ is greater than that of [M(H₂O)₆]²⁺.
- The acidity of [M(H₂O)₆]³⁺is greater than that of [M(H₂O)₆]²⁺ because the 3+ metal ions have higher charge density and have greater polarising power.
- The greater the polarising power, the more strongly it attracts the water molecule.
- This weakens the O-H bond so it breaks more easily releasing H⁺ ions.
Describe and explain the simple test-tube reactions of M²⁺ (aq) ions, limited to M = Fe and Cu, with limited OH⁻ and NH₃.
What are the colours of the precipitates formed?
If you were to add excess NH₃ to the product of the reaction between Cu²⁺ and OH⁻ / NH₃, what solution would form? What would its colour be?
- The bases OH⁻ and NH₃ when in limited amounts form the same hydroxide precipitates.
- They form in deprotonation acid-base reactions.
Fe
- [Fe(H₂O)₆]²⁺ (aq) + 2OH⁻ (aq) -> Fe(H₂O)₄(OH)₂ (s) + 2H₂O (I)
- [Fe(H₂O)₆]²⁺ (aq) + 2NH₃ (aq) -> Fe(H₂O)₄(OH)₂ (s) + 2NH₄⁺ (aq)
- Fe(H₂O)₄(OH)₂ (s) is a green precipitate.
Cu
- [Cu(H₂O)₆]²⁺ (aq) + 2OH⁻ (aq) -> Cu(H₂O)₄(OH)₂ (s) + 2H₂O (I)
- [Cu(H₂O)₆]²⁺ (aq) + 2NH₃ (aq) -> Cu(H₂O)₄(OH)₂ (s) + 2NH₄⁺ (aq)
- Cu(H₂O)₄(OH)₂ (s) is a blue precipitate.
Cu(H₂O)₄(OH)₂ with excess NH₃
- With excess NH₃, a ligand substitution reaction occurs with Cu and its precipitate dissolves to form a deep blue solution.
- Cu(H₂O)₄(OH)₂ + 4NH₃ (aq) -> [Cu(NH₃)₄(H₂O)₂]²⁺ (aq) + 2H₂O (I) + 2OH⁻
Describe and explain the simple test-tube reactions of M²⁺ (aq) ions, limited to M = Fe and Cu, with carbonate solutions (CO₃²⁻).
What are the colours of the precipitates formed?
- The 2⁺ ions with carbonate solution results in MCO₃ ppt being formed.
Fe
- Fe²⁺ (aq) + CO₃²⁻ (aq) -> FeCO₃ (s)
- [Fe(H₂O)₆]²⁺ + CO₃²⁻ -> FeCO₃ + 6H₂O
- FeCO₃ is a green precipitate.
Cu
- Cu²⁺ (aq) + CO₃²⁻ (aq) -> CuCO₃ (s)
- [Cu(H₂O)₆]²⁺ + CO₃²⁻ -> CuCO₃ + 6H₂O
- CuCO₃ is a blue precipitate.
Draw a summary of the simple test-tube reactions involving M²⁺ (aq) ions, limited to M = Fe and Cu.
Describe and explain the simple test-tube reactions of M³⁺ (aq) ions, limited to M = Al and Fe, with limited OH⁻ and NH₃.
What are the colours of the precipitates formed?
If you were to add excess OH⁻ to the product of the reaction between Al³⁺ and OH⁻ / NH₃, what solution would form? What would its colour be?
- The bases OH⁻ and NH₃ when in limited amounts form the same hydroxide precipitates.
- They form in deprotonation acid-base reactions.
Al
- [Al(H₂O)₆]³⁺ (aq) + 3OH⁻ (aq) -> Al(H₂O)₃(OH)₃ (s) + 3H₂O (I)
- [Al(H₂O)₆]³⁺ (aq) + 3NH₃ (aq) -> Al(H₂O)₃(OH)₃ (s) + 3NH₄⁺ (aq)
- Al(H₂O)₃(OH)₃ (s) is a white precipitate.
Fe
- [Fe(H₂O)₆]³⁺ (aq) + 3OH⁻ (aq) -> Fe(H₂O)₃(OH)₃ (s) + 3H₂O (I)
- [Fe(H₂O)₆]³⁺ (aq) + 3NH₃ (aq) -> Fe(H₂O)₃(OH)₃ (s) + 3NH₄⁺ (aq)
- Fe(H₂O)₃(OH)₃ (s) is a brown precipitate.
Al(H₂O)₃(OH)₃ with excess OH⁻
- With excess NaOH, the aluminium hydroxide dissolves and forms a colourless solution.
- Al(H₂O)₃(OH)₃ (s) + OH⁻ (aq) -> [Al(OH)₄]⁻ (aq) + 3H₂O (I)
Describe and explain the simple test-tube reactions of M³⁺ (aq) ions, limited to M = Al and Fe, with carbonate solutions (CO₃²⁻).
What are the colours of the precipitates formed?
- The 3⁺ ions with carbonate solution form a M(OH)₃ ppt and CO₂ gas is evolved.
Al
- 2[Al(H₂O)₆]³⁺ (aq) + 3CO₃²⁻ -> 2Al(H₂O)₃(OH)₃ (s) + 3CO₂ + 3H₂O (I)
- 2Al(H₂O)₃(OH)₃ is a white precipitate.
Fe
- 2[Fe(H₂O)₆]³⁺ (aq) + 3CO₃²⁻ -> 2Fe(H₂O)₃(OH)₃ (s) + 3CO₂ + 3H₂O (I)
- 2Fe(H₂O)₃(OH)₃ is a brown precipitate.
Why is MCO₃ formed with 2⁺ ions, but M₂(CO₃)₃ is not formed with 3⁺ ions?
- The difference is explained by the greater polarising power of the 3⁺ ions due to its higher charge density.
Draw a summary of the simple test-tube reactions involving M³⁺ (aq) ions, limited to M = Al and Fe.
