Reactions of inorganic compounds in aqueous solution

What is the definition of a Lewis acid?

Electron pair acceptors in the formation of dative covalent bonds.

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What is the definition of a Lewis base?

Electron pair donors in the formation of co-ordinate (dative) covalent bonds.

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How can water act as both a Lewis base and a Bronsted-Lowry base?

A water molecule has two lone pairs of electrons and it can use one of these to accept a proton (acting as a Lewis base & as a Bronste-Lowry base) or, e.g., to form a co-ordinate bond with a metal ion (acting as a Lewis base).

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Are all Bronsted-Lowry acids also Lewis acids?

Yes.

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According to the Lewis theory, what are the ligands that form bonds to transition metal ions acting as? What are the metal ions acting as?

The ligands are acting as Lewis bases. The metal ions are acting as Lewis acids.

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What are metal aqua ions? What would be the formula for the Fe^2+ hexa-aqua ion?

When six water molecules act as ligands bonding to the metal ion in an octahedral arrangement. They each use one of their lone pairs of electrons to form a co-ordinate (dative) bond with the metal ion (they're acting as Lewis bases). [Fe(H2O)6]^2+.

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Why is the Fe^3+ ion more acidic than the Fe^2+ ion?

Because the Fe^3+ ion is smaller and more highly charged than the Fe^2+ ion (it has a higher charge density), making it more strongly polarising.

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Why is Fe^3+(aq) acidic?

In the [Fe(H2O)6]^3+(aq) ion the iron strongly attracts electrons from the oxygen atoms of the water ligands, this weakens the O-H bonds in the water molecules. This complex ion will then readily release an H+ ion making the solution acidic.

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What is the equation for when the iron(III) hexa-aqua ion releases a H+ ion?

[Fe(H2O)6]^3+(aq) [Fe(H2O)5(OH)]^2+(aq) + H+(aq)

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What is the equation for the hydrolysis reaction that occurs between the iron(III) hexa-aqua ion and water?

[Fe(H2O)6]^3+(aq) + H2O(l) -----> [Fe(H2O)5(OH)]^2+(aq) + H3O+(aq)

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What happens if a base (e.g. OH-) is added to a transition metal ion in the +2 or +3 oxidation state?

The base will remove protons from the aqueous complex.

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What is the equation for the reaction between OH- and [M(H2O)6]^3+? ('M' represents a general transition metal ion).

[M(H2O)6]^3+(aq) + OH-(aq) -----> [M(H2O)5(OH)]^2+(aq) + H2O(l)

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What is the equation for the reaction between OH- and [M(H2O)5(OH)]^2+? ('M' represents a general transition metal ion).

[M(H2O)5(OH)]^2+(aq) + OH-(aq) -----> [M(H2O)4(OH)2]^+(aq) + H2O(l)

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What is the equation for the reaction between OH- and [M(H2O)4(OH)2]^+? ('M' represents a general transition metal ion).

[M(H2O)4(OH)2]^+(aq) + OH-(aq) -----> M(H2O)3(OH)3(s) + H2O(l)

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How else can M(H2O)3(OH)3 be written? What are some of the properties of this compound?

It's effectively M(OH)3, which is uncharged and insoluble and forms as a precipitate.

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What is the equation for the reaction between OH- and [M(H2O)6]^2+? ('M' represents a general transition metal ion).

[M(H2O)6]^2+(aq) + OH-(aq) -----> [M(H2O)5(OH)]^+(aq) + H2O(l)

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What is the equation for the reaction between OH- and [M(H2O)5(OH)]^+? ('M' represents a general transition metal ion).

[M(H2O)5(OH)]^+(aq) + OH-(aq) -----> M(H2O)4(OH)2(s) + H2O(l)

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How else can M(H2O)4(OH)2 be written? What are some properties of this species?

It's effictively M(OH)2, which is uncharged and insoluble and forms a precipitate.

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What has the same effect as OH- ions in removing protons?

Ammonia, which is basic.

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Is the CO3^2- ion a base or an acid?

A base.

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What's the equation for the reaction between iron(III) hexa-aqua ion and the carbonate ion?

[Fe(H2O)6]^3+(aq) +3CO3^2-(aq) Fe(OH)3(H2O)3(s) + 3HCO3^-(aq)

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What's the equation for the overall reaction between iron(III) hexa-aqua ion and the carbonate ion?

2[Fe(H2O)6]^3+(aq) + 3CO3^-(aq) -----> 2[Fe(H2O)3(OH)3](aq) + 3CO2(g) + 3H2O(l)

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Which tend to exist, carbonates of transition metal ions in oxidation state +2 or ions in the +3 oxidation stae?

In general, carbonates of transition metal ions in oxidation state +2 exist, while those of ions in the +3 state do not.

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What is the equation for the reaction between H3O+ ions and CO3^2- ions?

2H3O+(aq) + CO3^2-(aq) -----> 3H2O(l) + CO2(g)

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What is the equation for the reaction between [Fe(H2O)6]^3+ and carbonate ions? What is the product that's formed?

[Fe(H2O)6]^3+(aq) + CO3^2-(aq) -----> FeCO3(s) + 6H2O(l). The product is insoluble iron(II) carbonate.

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What is the colour of [Fe(H2O)6]^2+(aq)?

Pale green.

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What is the colour of [Fe(H2O)6]^3+(aq)?

Pale brown.

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What is added to distinguish between solutions of What is the colour of [Fe(H2O)6]^2+ ions and [Fe(H2O)6]^3+ ions? Why is this added?

Dilute alkali is added, as this precipitates the hydroxides whose colours are more obviously different.

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What product is formed when [Fe(H2O)6]^2+ ions react with OH- ions, in the test for iron ions? What is the colour of this precipitate?

Fe(H2O)4(OH)2(s) (+ 2H2O(l)). The precipitate is green.

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What product is formed when [Fe(H2O)6]^3+ ions react with OH- ions, in the test for ir(on ions? What is the colour of this precipitate?

Fe(H2O)3(OH)3(s) (+ 3H2O(l)). The precipitate is brown.

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What does amphoteric mean?

Showing both acidic and basic properties.

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Why can aluminium hydroxide be described as amphoteric?

Becuase it'll react with both acids and bases.

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What is the equation for the reaction between aluminium hydroxide and HCl?

Al(H2O)3(OH)3 + 3HCl -----> Al(H2O)6^3+ + 3Cl-

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What is the equation for the reaction between aluminium hydroxide and sodium hydroxide?

Al(H2O)3(OH)3 + OH- -----> [Al(OH)4]^- + 3H2O(l)

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Does chromium hydroxide show amphoteric properties?

Yes.

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Is a cation a positive or negative ion?

Positive ion.

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Is an anion a positive or negative ion?

Negative ion.

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Are the ionsMnO4^-, CrO4^- and Cr2O7^2- cations or anions?

They're anions.

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For what 2 reasons can the water molecules acting as ligands in metal aqua ions be replace by other ligands?

Either because the other ligands form stronger co-ordinate bonds (are better Lewis bases) or because they are present in higher concentration and an equilibrium is displaced.

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What are the four possibilities that can replace water molecules in metal aqua ions?

They can be replaced by other neutral ligands (e.g. ammonia), or by negatively charged ligands (e.g. Cl-), or by bi- or multidentate ligands (chelation), replacement of water molecules may be complete or partial.

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In general, for an M^2+ ion, how are water molecules replacd by ammonia molecules? Why is there no change in co-ordination number or charge on the ion?

Water molecules are replaced one at a time by ammonia. Both ligands are uncharged and of similar size.

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What is the equation for the overall reaction between a M^2+ hexa-aqua ion and ammonia?

[M(H2O)6]^2+(aq) + 6NH3(aq) [M(NH3)6]^2+(aq) + 6H2O(l)

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What is the complication when ammonia is used as a ligand?

Ammonia is also a base, and therefore contains OH- ions.

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What is the equation for the reaction between [M(H2O)6]^2+ and OH- ions (that come from ammonia acting as a base)?

[M(H2O)6]^2+ + 2OH-(aq) -----> M(H2O)4(OH)2(s) + 2H2O(l)

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What's the equation for the reaction between M(H2O)4(OH)2 and ammonia?

M(H2O)4(OH)2(s) + 6NH3(aq) [M(NH3)6]^2+(aq) + 4H2O(l) + 2OH-(aq)

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What is the equation for the first step in the reaction between [Co(H2O)6]^2+ and ammonia? What colour is the complex ion formed and what is its name?

[Co(H2O)6]^2+ + 2NH3(aq) -----> [Co(H2O)4(OH)2]. The product is a blue precipitate of cobalt(II) hydroxide.

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What happens to both the OH- ions and the four water ligands in [Co(H2O)4(OH)2] when more concentrated ammonia is added? What are the two reasons for this occuring?

Both the OH- ions and the four water ligands are replaced by ammonia, because; ammonia is a better ligand, & the high conc of ammonia displaces the equilibria, thus displacing water and OH-.

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What is the equation for the overall reaction of hydrated cobalt(II) hydroxyde and excess ammonia? What is the colour of the complex ion formed?

[Co(H2O)4(OH)2](s) + 6NH3(aq) [Co(NH3)6]^2+(aq) + 4H2O(l) + 2OH-(aq). The complex ion is a pale yellow solution.

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What is the colour of a solution of Co^3+ ions?

Brown.

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What is the equation for the overall reaction between copper(II) hexa-aqua ions and ammonia? What colour is the complex ion that is formed?

[Cu(H2O)6]^2+(aq) + 4NH3(aq) [Cu(NH3)4(H2O)2]^2+(aq) + 4H2O(l). The complex ion formed is a very deep purple colour.

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What is the colour of [Cu(H2O)6]^2+?

Pale blue solution.

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What is formed when the copper(II) hexa-aqua ion reacts with ammonia, which firstly acts as a base? What is the colour of the complex ion formed?

[Cu(OH)2(H2O)4](s). This is copper hydroxide and it's a pale blue precipitate.

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When excess concentrated ammonia is added to copper hydorxide, the precipitate dissolves. What is the equation for this reaction?

[Cu(OH)2(H2O)4](s) + 4NH3(aq) [Cu(NH3)4(H2O)2]^2+(aq) + 2H2O(l) + 2OH-(aq)

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What is the shape of the [Cu(NH3)4(H2O)2]^2+ ion?

Octahedral. The four ammonia molecules exist in a square planar arrangement with the two water molecules a ove and below the plane.

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Why are the Cu-O bonds longer, and therefore weaker, than the Cu-N bonds in [Cu(NH3)4(H2O)2]^2+?

Because water is a poorer ligand.

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What is the equation for the overall reaction between aqueous copper(II) ions and concentrated hydrochloric acid? What is the colour of the complex ion formed?

[Cu(H2O)6]^2+(aq) + 4Cl-(aq) [CuCl4]^2-(aq) + 6H2O(l). The complex ion formed is yellow.

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What does the co-ordination number change to in the reaction between aqueous copper(II) ions and comcentrated hydrochloric acid? Why is there a change in co-ordination number?

It goes from six co-ordinate, in [Cu(H2O)6]^2+(aq), to four co-ordinate, in [CUCl4]^2-(aq). Because Cl- is larger than H2O and fewer ligands can physically fit around the central copper ion.

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What is the shape of the [CUCl4]^2- ion?

Tetrahedral.

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What is chelation?

Chelation is the formation of complexes with multidentate ligands.

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What are multidentate ligands?

They're ligands with more than one lone pair of electrons so that they can form more than one co-ordinate bond.

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Are complexes with multidnetate or monodentate ligands more stable? Why?

Complexes with multidentate ligands are usually more stable than those with monodentate ligands. This is due to the entropy change of the reaction.

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What is the short-hand way of writing ethylene diamine?

'en'.

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What is the colour and formula of the complex formed when [Fe(H2O)6]^2+(aq) reacts with a little OH-?

Green gelatinous precipitate of Fe(H2O)4(OH)2.

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What is the colour and formula of the complex formed when [Fe(H2O)6]^2+(aq) reacts with excess OH-?

Green gelatinous precipitate of Fe(H2O)4(OH)2.

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What is the colour and formula of the complex formed when [Fe(H2O)6]^2+(aq) reacts with a little NH3?

Green gelatinous precipitate of Fe(H2O)4(OH)2.

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What is the colour and formula of the complex formed when [Fe(H2O)6]^2+(aq) reacts with excess NH3?

Green gelatinous precipitate of Fe(H2O)4(OH)2.

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What soon happens to pale green Fe(H2O)4(OH)2?

It's soon oxidised by air to brown Fe(H2O)3(OH)3.

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What is the colour and formula of the complex formed when [Fe(H2O)6]^2+(aq) reacts with CO3^2-?

Green precipitate of FeCO3.

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What is the colour of [Co(H2O)6]^2+(aq)?

Pink.

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What is the colour and formula of the complex formed when [Co(H2O)6]^2+(aq) reacts with a little OH-?

Blue precipitate of Co(H2O)4(OH)2.

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What is the colour and formula of the complex formed when [Co(H2O)6]^2+(aq) reacts with excess OH-?

Blue precipitate of Co(H2O)4(OH)2.

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What is the colour and formula of the complex formed when [Co(H2O)6]^2+(aq) reacts with a little NH3?

Blue precipitate of Co(H2O)4(OH)2.

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What is the colour and formula of the complex formed when [Co(H2O)6]^2+(aq) reacts with excess NH3?

Pale yellow-brown solution of [Co(NH3)6)^2+(aq)

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What usually happens to a solution of [Co(NH3)6]^2+(aq)?

It's oxidised by air to a dark brown mixture containing Co(III) compounds.

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What is the colour and formula of the complex formed when [Cu(H2O)6]^2+(aq) reacts with a little OH-?

Pale blue precipitate of Cu(H2O)4(OH)2.

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What is the colour and formula of the complex formed when [Cu(H2O)6]^2+(aq) reacts with excess OH-?

Pale blue precipitate of Cu(H2O)4(OH)2.

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What is the colour and formula of the complex formed when [Cu(H2O)6]^2+(aq) reacts with a little NH3?

Pale blue precipitate of Cu(H2O)4(OH)2.

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What is the colour and formula of the complex formed when [Cu(H2O)6]^2+(aq) reacts with excess NH3?

Deep blue solution of [Cu(NH3)4(H2O)2]^2+(aq)

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What is the colour and formula of the complex formed when [Cu(H2O)6]^2+(aq) reacts with CO3^2-?

Blue-green precipitate of CuCO3.

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What is the colour of the complex ion [Fe(H2O)6]^3+(aq)?

Purple/yellow/brown.

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What is the colour and formula of the complex formed when [Fe(H2O)6]^3+(aq) reacts with a little OH-?

Brown gelatinous precipitate of Fe(H2O)3(OH)3.

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What is the colour and formula of the complex formed when [Fe(H2O)6]^3+(aq) reacts with excess OH-?

Brown gelatinous precipitate of Fe(H2O)3(OH)3.

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What is the colour and formula of the complex formed when [Fe(H2O)6]^3+(aq) reacts with a little NH3?

Brown gelatinous precipitate of Fe(H2O)3(OH)3.

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What is the colour and formula of the complex formed when [Fe(H2O)6]^3+(aq) reacts with excess NH3?

Brown gelatinous precipitate of Fe(H2O)3(OH)3.

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What is the colour and formula of the complex formed when [Fe(H2O)6]^3+(aq) reacts with CO3^2-?

Brown gelatinous precipitate of Fe(H2O)3(OH)3 + bubble of CO2.

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What is the colour of the [Al(H2O)6]^3+(aq) ion?

It's colourless.

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What is the colour and formula of the complex formed when[Al(H2O)6]^3+(aq) reacts with a little OH-?

White precipitate of Al(H2O)3(OH)3.

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What is the colour and formula of the complex formed when[Al(H2O)6]^3+(aq) reacts with excess OH-?

Colourless solution of [Al(OH)4]^-.

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What is the colour and formula of the complex formed when[Al(H2O)6]^3+(aq) reacts with a little NH3?

White precipitate of Al(H2O)3(OH)3.

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What is the colour and formula of the complex formed when[Al(H2O)6]^3+(aq) reacts with excess NH3?

White precipitate of Al(H2O)3(OH)3.

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What is the colour and formula of the complex formed when[Al(H2O)6]^3+(aq) reacts with CO3^2-?

White precipitate of Al(H2O)3(OH)3 + bubbles of CO2.

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What's the colour of the [Cr(H2O)6]^3+(aq) ion?

Ruby.

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What is the colour and formula of the complex formed when [Cr(H2O)6]^3+(aq) reacts with a little OH-?

Green precipitate of Cr(H2O)3(OH)3.

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What is the colour and formula of the complex formed when [Cr(H2O)6]^3+(aq) reacts with excess OH-?

Green solution of [Cr(OH)6]^3-.

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What is the colour and formula of the complex formed when [Cr(H2O)6]^3+(aq) reacts with a little NH3?

Green precipitate of Cr(H2O)3(OH)3.

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What is the colour and formula of the complex formed when [Cr(H2O)6]^3+(aq) reacts with excess NH3?

Purple solution of [Cr(NH3)6]^3+.

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What is the colour and formula of the complex formed when [Cr(H2O)6]^3+(aq) reacts with CO3^2-?

Green precipitate of Cr(OH)3 + bubbles of CO2.

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Reactions of inorganic compounds in aqueous solution

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