Reactions of Inorganic Compounds in Aqueous Solutions

Vocabulary flashcards covering the acid-base chemistry, Lewis/Br%nsted theories, and ligand substitution reactions of transition metal aqua ions.

Aqua ions

Complex ions formed when water molecules act as ligands, bonding to a central metal ion (such as $Fe^{2+}$ or $Fe^{3+}$) in an octahedral arrangement using lone pairs to form co-ordinate bonds.

Hydrolysis

A reaction with water in which $O-H$ bonds are broken and new species are formed; for example, $[Fe(H_2O)_6]^{3+}(aq) \rightleftharpoons [Fe(H_2O)_5(OH)]^{2+}(aq) + H^+(aq)$.

Charge density

A property determined by the size and charge of an ion; $Fe^{3+}$ has a higher charge density than $Fe^{2+}$ because it is smaller and more highly charged, making it more strongly polarising.

Br%nsted-Lowry acid

A substance defined as a proton ($H^+$ ion) donor.

Lewis acid

An electron pair acceptor in the formation of a co-ordinate (dative) covalent bond.

Lewis base

An electron pair donor in the formation of a co-ordinate (dative) covalent bond; ligands often act as Lewis bases.

Amphoteric

Showing both acidic and basic properties; for example, aluminium hydroxide reacts with both acids ($HCl$) and bases ($NaOH$).

Ligand substitution

A process where water molecules in a metal aqua ion are replaced by other ligands like ammonia ($NH_3$), chloride ions ($Cl^-$), or multidentate ligands.

Chelation

The formation of complexes with multidentate ligands, which are typically more stable than monodentate complexes due to a positive change in entropy.

Bidentate ligand

A ligand with more than one lone pair that can form two co-ordinate bonds; an example is ethylene diamine (en), with the formula $H_2NCH_2CH_2NH_2$.

Hexadentate ligand

A single ligand that can displace six water ligands from an aqua ion, such as $EDTA^{4-}$.

$$[Cu(NH_3)_4(H_2O)_2]^{2+}$$

A deep blue octahedral complex with a square-planar arrangement of four ammonia ligands and two water molecules above and below the plane; its $Cu-O$ bonds are longer and weaker than the $Cu-N$ bonds.

$$[CuCl_4]^{2-}$$

A yellow, four co-ordinate tetrahedral complex formed because $Cl^-$ ions are larger than $H_2O$ molecules, meaning fewer ligands can fit around the central copper ion.

Metal(II) Carbonates

Insoluble solids like $FeCO_3$ that form when carbonate ions react with $M^{2+}$ aqua ions; in contrast, $M^{3+}$ ions are too acidic to form carbonates and release $CO_2$ gas instead.