Chemistry › Definitions › Ions in aqueous solution

Ions in aqueous solution definitions

Every term the lessons in this unit define, lesson by lesson, worded as the lessons use them. Each lesson title links to its notes.

19 terms

Metal-aqua ions and the acidity of their solutions

Metal-aqua ion: A complex ion in which water molecules are the ligands, each bonded to the central metal ion by a coordinate bond from a lone pair on its oxygen atom.
Ligand: A molecule or ion that donates a lone pair of electrons to a central metal ion to form a coordinate bond.
Coordinate bond: A covalent bond in which both electrons of the shared pair come from the same atom.
Coordination number: The number of coordinate bonds from the ligands to the central metal ion; six in a hexaaqua ion.
Hydrolysis (of a metal-aqua ion): The reaction of a metal-aqua ion with water in which a coordinated water molecule loses a proton to a solvent water molecule, forming H₃O⁺.
Brønsted–Lowry acid: A species that donates a proton (an H⁺ ion) to another species.
Weak acid: An acid that is only partially dissociated in solution, so the equilibrium lies to the left.
Charge/size ratio: The charge on an ion divided by its radius; also called charge density. A small, highly charged ion has a high ratio.
Polarisation: The distortion of the electron density in a bond by a nearby charge, which makes the bond more polar and here weakens it.
Acid dissociation constant, Ka: The equilibrium constant for the dissociation of a weak acid, Ka = [H⁺][A⁻] ÷ [HA]; a larger Ka means a stronger acid.

Brønsted–Lowry base: A species that accepts a proton (an H⁺ ion) from another species.
Precipitate: An insoluble solid that forms when two solutions are mixed.
Deprotonation: The removal of a proton from a species; here, from a water ligand bonded to a metal ion, leaving a hydroxide ligand.
Amphoteric: Able to react both as an acid and as a base; aluminium hydroxide dissolves in acids and in excess alkali.
Excess (of a reagent): More of a reagent than is needed to react with all of the other reactant present.
Ligand substitution: A reaction in which one ligand in a complex ion is replaced by another, such as ammonia replacing water around copper(II).
Weak base: A base that is only partially protonated in solution; aqueous ammonia holds far fewer OH⁻ ions than sodium hydroxide of the same concentration.
Effervescence: Bubbles of gas produced in a liquid by a reaction; here carbon dioxide, which turns limewater milky.
Aerial oxidation: Oxidation of a substance by oxygen from the air; the hydroxides of iron(II), manganese(II) and cobalt(II) darken on standing because of it.