Aqueous reactions
& Solution
stoichiometry
, Aqueous reactions
Properties of aqueous solutions
Solution: homogeneous mixture of two/more pure substances.
Solvent: component present in the greater quantity.
Solute: substance that dissolves in the solvent.
When water is the solvent, the solution, called an aqueous solution (aq).
Electrolytes
Electrolytes: Substances/solutes that form ions in water, solutions conduct electricity, ions carry electrical
charge from one electrode to another.
Electrolyte strength depends on: ions in solution & charge of ions
Non-electrolytes: Substances/solutes that do not form ions in water. eg, sugar (s) -> sugar (aq)
Pure water & non-electrolytes do not conduct electricity as they do not form ions in water
Solvation
Substances dissolve by solvation surrounding of solute by solvent.
Way solvation occurs depends on the type of compound
Ionic compounds (metals & non-metals) dissolve by dissociation, water surrounds separated ions.
Molecular compounds interact with water, most do NOT dissociate.
Dissociation of ionic compounds Interaction of molecular compounds
Ionic compound is dissolved in water, it dissociates into ions Most molecular compounds do not form ions in water
Ions evenly disperse throughout solution Therefor they’re non-electrolytic.
Surrounding water molecules prevent compound from recombining However, some do ionise in water.
Water molecules orientate to stabilise electrostatic attractions, Eg : HCl (aq) —> H+ (aq) + Cl- (aq)
δ- side interacts with + ions, δ+ side interacts with - ions
Identifying electrolytes
Strong electrolyte dissociate/ionise completely
Single-headed arrow: indicate that ions have no tendency to
e.g. HCl (aq) —> H+(aq) + Cl-(aq) recombine, represents ionisation of strong electrolyte.
e.g. Ba(OH) 2 (s) —> Ba2+ (aq) + 2OH- (aq) Single-headed arrow used for non-electrolytes too.
Weak electrolyte only dissociates/ionises partially Double-headed arrow in opposite directions: demonstrates
An chemical equilibrium between molecules & ions equilibrium exists, represents ionisation of weak electrolyte.
e.g. CH3COOH (aq) + H2O (ℓ) ⇌ CH3COO- (aq) + H3O+ (aq)
Non-electrolytes do NOT dissociate in water
If a substance is ionic, expected to be a strong electrolyte
If a substance is molecular consider: Strength of acid =strength of
electrolyte
If it is an acid, identify if it’s a strong or weak acids.
If it is not an acid, probably weak electrolyte
Major types of reactions
Three types of reactions occur in aqueous solutions:
Precipitation reactions: Acid-base reactions: Oxidation–reduction (redox) reactions:
two ionic solutions mixed —> solid involve transfer of a proton. involve transfer of electrons between reactants.
ionic substance (precipitate) forms.
& Solution
stoichiometry
, Aqueous reactions
Properties of aqueous solutions
Solution: homogeneous mixture of two/more pure substances.
Solvent: component present in the greater quantity.
Solute: substance that dissolves in the solvent.
When water is the solvent, the solution, called an aqueous solution (aq).
Electrolytes
Electrolytes: Substances/solutes that form ions in water, solutions conduct electricity, ions carry electrical
charge from one electrode to another.
Electrolyte strength depends on: ions in solution & charge of ions
Non-electrolytes: Substances/solutes that do not form ions in water. eg, sugar (s) -> sugar (aq)
Pure water & non-electrolytes do not conduct electricity as they do not form ions in water
Solvation
Substances dissolve by solvation surrounding of solute by solvent.
Way solvation occurs depends on the type of compound
Ionic compounds (metals & non-metals) dissolve by dissociation, water surrounds separated ions.
Molecular compounds interact with water, most do NOT dissociate.
Dissociation of ionic compounds Interaction of molecular compounds
Ionic compound is dissolved in water, it dissociates into ions Most molecular compounds do not form ions in water
Ions evenly disperse throughout solution Therefor they’re non-electrolytic.
Surrounding water molecules prevent compound from recombining However, some do ionise in water.
Water molecules orientate to stabilise electrostatic attractions, Eg : HCl (aq) —> H+ (aq) + Cl- (aq)
δ- side interacts with + ions, δ+ side interacts with - ions
Identifying electrolytes
Strong electrolyte dissociate/ionise completely
Single-headed arrow: indicate that ions have no tendency to
e.g. HCl (aq) —> H+(aq) + Cl-(aq) recombine, represents ionisation of strong electrolyte.
e.g. Ba(OH) 2 (s) —> Ba2+ (aq) + 2OH- (aq) Single-headed arrow used for non-electrolytes too.
Weak electrolyte only dissociates/ionises partially Double-headed arrow in opposite directions: demonstrates
An chemical equilibrium between molecules & ions equilibrium exists, represents ionisation of weak electrolyte.
e.g. CH3COOH (aq) + H2O (ℓ) ⇌ CH3COO- (aq) + H3O+ (aq)
Non-electrolytes do NOT dissociate in water
If a substance is ionic, expected to be a strong electrolyte
If a substance is molecular consider: Strength of acid =strength of
electrolyte
If it is an acid, identify if it’s a strong or weak acids.
If it is not an acid, probably weak electrolyte
Major types of reactions
Three types of reactions occur in aqueous solutions:
Precipitation reactions: Acid-base reactions: Oxidation–reduction (redox) reactions:
two ionic solutions mixed —> solid involve transfer of a proton. involve transfer of electrons between reactants.
ionic substance (precipitate) forms.
