What is a ligand substitution reaction?

A ligand substitution reaction is a chemical reaction in which one ligand in a complex ion is replaced by another ligand.

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Describe the colour changes, and give the equation, for the reaction between aqueous ammonia (NH3) and [Cu(H2O)6]2+.

A pale blue precipitate of Cu(OH)2 forms initially. When ammonia is added in excess, the precipitate redissolves to form a dark blue solution.

[Cu(H2O)6]2+(aq) + 4NH3(aq) ➔ [Cu(NH3)4(H2O)2]2+(aq) + 4H2O(l)

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Why does the exchange of H2O with NH3 not affect the coordination number around the central metal ion?

Both H2O with NH3 ligands are similar in size.

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Describe the colour change, and give the equation, for the reaction between excess concentrated hydrochloric acid and [Cu(H2O)6]2+.

The solution turns from pale blue to yellow.

[Cu(H2O)6]2+(aq) + 4Cl-(aq) ➔ [CuCl4]2−(aq) + 6H2O(l)

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State and explain how the exchange of H2O with Cl- affects the coordination number around the central metal ion.

The exchange of H2O with Cl- decreases the coordination number (typically from six to four).


This is because Cl- ligands are larger than H2O ligands so fewer Cl- ligands can fit around the central metal ion.

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Describe, and give the equation for, the reaction between excess hydroxide ions and [Cu(H2O)6]2+.

A pale blue precipitate of Cu(H2O)4(OH)2(s) forms from a pale blue solution.

[Cu(H2O)6]2+(aq) + 2OH-(aq) ➔ Cu(H2O)4(OH)2(s) + 2H2O(l)

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Describe the colour changes, and give the equation, for the reaction between aqueous ammonia (NH3) and [Cr(H2O)6]3+.

A dark green precipitate of Cr(OH)3(H2O)3 forms initially. When ammonia is added in excess, the precipitate redissolves to form a purple solution.

[Cr(H2O)6]3+(aq) + 6NH3(aq) ➔ [Cr(NH3)6]3+(aq) + 6H2O(l)

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What is the role of iron(II) in hemoglobin?

Iron(II) in hemoglobin reversibly binds to oxygen molecules, allowing for efficient oxygen transport from the lungs to body tissues.

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Explain, in terms of ligand substitution, why carbon monoxide is toxic.

Carbon monoxide is toxic because it can bind to the iron(II) ion in hemoglobin more strongly than oxygen. This prevents oxygen transport and leads to oxygen deprivation in body tissues.

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What is the formula of the precipitate formed when aqueous [M(H2O)6]2+ ions react with hydroxide ions?

[M(H2O)4(OH)2


This could also be written as M(OH)2.

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Describe how you can distinguish between dilute aqueous solutions of Fe2+ and Fe3+.

  • Add sodium hydroxide (NaOH).
  • Fe2+ forms a green precipitate of iron(II) hydroxide.
  • Fe3+ forms a brown precipitate of iron(III) hydroxide.

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What is the formula of the precipitate formed when aqueous [M(H2O)6]3+ ions react with hydroxide ions?

[M(H2O)3(OH)3


This could also be written as M(OH)3.

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Describe the colour changes, and give the equation, for the reaction between aqueous concentrated ammonia (NH3) and [Fe(H2O)6]3+.

A brown precipitate of Fe(H2O)3(OH)3 forms form a yellow solution.

[Fe(H2O)6]3+(aq) + 3NH3(aq) ➔ Fe(H2O)3(OH)3(s) + 3NH4+(aq)

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