Reactions of Inorganic Compounds in Aqueous Solutions Flashcards
Why are M3+ aqua ions more acidic than M2+ aqua ions?
The M3+ ion is smaller and more highly charged so has a greater charge density making it more strongly polarising. Therefore the the metal in the complex strongly attracts the electrons from the oxygen atoms of the water ligands which weakens the O-H bonds in the water molecules. The complex ion will then readily release a H+ ion making the solution acidic (can happen in more than 1 water molecule). M2+ less polarising so fewer O-H bonds broken.
What happens when M3+ aqua ions are reacted with OH- ions?
3 water ligand have protons removed by the OH- ions and become OH- ligands (one at a time). 3 waters are formed from the protons and added OH- ions. The neutral metal (3) hydroxide is formed, M(H2O)3(OH)3, which is insoluble and forms as a precipitate.
What happens when M2+ aqua ions are reacted with OH- ions?
2 water ligands have protons removed by the OH- ions and become OH- ligands (one at a time). 2 waters are formed from the protons and added OH- ions. The neutral metal (2) hydroxide is formed, M(H2O)3(OH)3, which is insoluble and forms as a precipitate.
What effect does adding ammonia to metal aqua ions have?
The same effect as adding OH- ions. But ammonium ions are formed instead of water.
What happens when M3+ aqua ions are reacted with carbonate ions?
The solution fizzes due to CO2 being released. The carbonate ion is able to remove protons from a M3+ aqua ion to form a hydrated M(3) hydroxide. This is insoluble in water so forms as a precipitate. Water is also formed.
What happens when M2+ aqua ions are reacted with carbonate ions?
The carbonate ions can’t remove protons from the complex. A metal carbonate is formed instead which is insoluble in water so forms as a precipitate. Water is also formed but CO2 isn’t so no bubbles.
How to distinguish between Fe2+ and Fe3+ aqua ions
Add dilute alkali. Fe3+ forms a brown precipitate. Fe2+ forms a green precipitate.
Reactions to show aluminium hydroxide precipitate is amphoteric
Acts as base when reacted with HCl, forms the Al3+ aqua ion.
Acts as an acid when reacted with excess OH- ions to form [Al(OH)4]- and 3 waters.
Why does the coordination number of the complex not change when water molecules are replaced by ammonia molecules through ligand substitution?
The molecules are of similar size so the same number can fit around the metal.
Why does ligand substitution take place when excess concentrated ammonia is added to aqua ions?
Ammonia is a better ligand than water as the lone pair is less strongly held than that of the more electronegative oxygen atom of water.
Why is the shape of a complex with 4 ammonias and 2 waters distorted?
The 4 ammonias exist as a square planar arrangement around the metal with the 2 waters above and below the plane to make an octahedral shape. The M-O bonds and longer and therefore weaker than the M-N bonds as water is a poorer ligand. Therefore the octahedron is slightly distorted.
What happens when ammonia is added to copper aqua ions?
Start with pale blue solution. Then we see a pale blue precipitate due to the ammonia removing two protons from the water ligands. When more ammonia (conc) is added, the precipitate dissolves to form a deep blue solution because 4 ammonias have displaced the 2 hydroxide ions and 2 water ligands. Two water ligands remain so the ligand substitution is only partial.
What is haem?
An iron(2) complex with a multidentate ligand.
Describe the structure of haemoglobin
Fe2+ ion with coordination number of 6. 4 of the coordination sites are taken up by a ring system called porphyrin (bonds using Ns). Below the plane of this ring is a 5th N acting as a ligand which is part of a protein called globin. The 6th site is free to accept an oxygen molecule as a ligand.
How does the transport of oxygen work with haemoglobin?
The 6th coordination site on the Fe2+ ion can accept and O2 molecule as a ligand. The Fe2+ to O2 bond is weak as O2 isn’t a very good ligand so the O2 molecule can easily be given up to cells.
